Archive for Laser Beam Scanning Projectors

Celluon Laser Beam Scanning Projector Technical Analysis – Part 1

Celluon Light Path w800 IMG_8087The Celluon PicoPro projector has been out for a few months now for about $359.   I have read a number of so-called “reviews” that were very superficial and did little more than turn on the projector and run a few pictures and maybe make a video.   But I have not seen any serious technical analysis or review that really showed the resolution or measured anything beyond the lumens.   So I am going to be doing a multi-part technical analysis on this blog (there is just too much to cover in one article).

In the photo at the top, I took a picture with the lasers on to more clearly see the various light paths.  A surprise to many is that they used 5 lasers and not just three which adds to the cost and complexity of the design.   They use two red and green lasers to get to the spec’ed (and measured) brightness of 32 lumens.   In future articles, I will get into more details on the optical path and what is going on (there are a few “tricks” they are using).

It is no secret by now that the Celluon engine uses a beam scanning mirror from Microvision and the optical engine and electronics are from Sony (the engine looks identical to the one Sony Announced February 20, 2014) .  Below I have taken the cover off the electrical part so you can see some of the chips. If you look carefully at the red arrows in the picture below, you can see the 3 clearly identified Sony ASICs used in the driver board (the 4th large chip is a Samsung SDRAM and the smaller device is a Texas Instruments power supply chip — there are more power supply chips on the backside of the board).

Sony Devices IMG_9737

I have used test charts to measure the resolution, check the color control , and measured the power consumption.   I have also taken a look inside to see how it is made (per the pictures above).    I have collected data and many images so the biggest problem for me to boil  this down into a manageable form for presentation on this blog.   I decide to start with just a bit about the resolution and a summary of some other issues.

Celluon claims the resolution is “1920 x 720” pixels and not that is not a typo on my part, they really claim to have “1920” horizontal resolution with as claimed by Sony in a press release on the engine.  It is easily provable that the horizontal resolution is much less than 1920 or even 1280 pixels and the vertical resolution is not up to fully resolving 720 lines.   In fact the effective/measurable resolution of the Celluon engine is closer to 640 by 360 pixels than it is to 1280×720.

PC Magazine’s April 22, 2015 article on the Celluon PicoPro made the oxymoron statement “the image has a slight soft-focus effect.”  To me “soft-focus” means blurry and indeed the image is in fact both blurry and lower in resolution.   The article also stated “I also saw some reddish tinges in dark gray areas in some images, a problem that also showed up in a black-and-white movie clip“.   The image is definitely “off to the red” (white point at about 4000K) and it has very poor color control in the darker areas of the gray-scale.

Resolution is a big topic and I have a lot of photos, but to get things started, below I have taken a center crop of 1280×720 HDMI input into the Cellulon projector.   Below this image I have included the same crop of the text pattern in put zoomed in by 2X for comparison.   In the photo you will see a yellow measuring tape that was flush against the projection screen, this both shows the size of the projected image AND proves that the camera was focused well and had enough resolution to show pixels in the projected image.

Celluon test pattern comparison

720P Celluon Projected Image with Source Below It with key comparison point indicated by the red ovals

You might want to look at the various areas indicated by the red ovals corresponding to the same areas of the projected image and the test pattern.  What you can see is that there is effectively no modulation/resolution of the sets of 1 pixel wide vertical lines so the horizontal resolution is below 1280 (more like about half 1280).

There is some modulation, but not as much as you should get if this were truly 720p, of the horizontal lines center of the of the image but this will fade out towards the left and right side of the projected image (I will get into this more in a future article).

You may also notices that the overall Celluon image is blurry.  Yes, I know lasers are supposed to “always be in focus,” but the image is definitely out of focus.   It turns out that at the size of this image (12 inches vertical or 24 inches diagonal which is moderately big, the width of the scanned laser beams are wider than a pixel and thus overlap.

The image is even more blurry if the image is say about 7-inches high projected on a standard letter size sheet of paper (the image is very blurry).  The blurriness goes down if the image gets bigger but it is NEVER really sharp even with a 72-inch diagonal image.   In a future article I will post the same test pattern at different image sizes to show the effects of image size and blurriness/focus.  I have started to call this “never in-focus technology.”

Some summary observations (more to come on these subjects):

  1. Laser Speckle – much improved over previous Microvision ShowWX projectors.   It still is far from perfect an most annoying where there are large flat areas and text on a bright background.
  2. The Celluon eliminated the “bowtie” effect of earlier Microvision ShowWX product so that the image is rectangular
  3. The lost the 100% offset of the ShowWX meaning that this requires a “stand” and the image will either be keystone or the projector will be between the viewers eye and the image.  This is bad/wrong for a short throw projector.  There is no keystone correction supported by the product.
  4. Low effective resolution – absolutely nowhere close to 720p (see above, more on this in future articles).
  5. Blurry image – not the same per se as resolution.  The size of the laser beam appears to be bigger than a pixel until the image is very large.  Additionally there are issues with aligning the 5 lasers into a single “beam” and issue with the interlaced bi-directional scan process (see for more on the scan process and how it hurts resolution).
  6. Class 3R laser product – This is a very serious problem as it is not safe for use with children (in fact laser safety glasses are recommended) but it this is not well marked.  The labels on the product are ridiculously tiny (particularly the one on the projector itself).  The EU is reported in the process of banning consumer products that emit 3R laser light ( and
  7. Flicker – this is a serious problem with this product and I will discuss more about this in a later article.  About 1 in 7 people I showed the projector to said it gave them headaches or other problems (I had multiple people tell me to turn it off as it was painful to even be in the room with it).  The scan process is 60-hertz “interlaced” with no persistence (as with an old CRT).
  8. The power consumption is high taking about 2.6W to show a totally back image and 6.1W for a totally white 32 lumen image with the power consumption in between roughly proportional to the image content. Don’t let the lack of fans fool you, they are using heat spreading over the entire package to dissipate the heat from just the projector.  The device will quickly overheat if left on a tabletop (as opposed to the fan) as much of the heat is spread over the bottom of the package.  It will also overheat if a bright image is left on the screen for too long even if the device is floating in air.
  9. The color/gray scale control is pretty poor particularly with the darker parts of a gray ramp.  At the dark end of the gray scale the “gray” turns red.  Additionally there is “crosstalk” caused from the lasers heating or cooling based on the brightness on one part of the screen that affects the color/brightness on the other side of the screen.   In other words the content of the image in one area will affect the color in another area (particularly horizontally).

I have seen Microvision laser scanned projectors since the Microvision ShowWX came out in 2010 or 5 years ago and the Celluon unit has many of the same issues that I found with the ShowWX.  While the Celluon is much improved in terms of brightness and speckle, has better resolution (but not as near what is claimed) and it delivers about 3X the brightness for the about the same power (much of this is due to laser improvements over the last 5 years) the progress is very modest considering that 5 years have passed.

Frankly, I still consider this technology far from ready for “prime time” high volume and sill has some major and in many ways fatal flaws.  Being laser safety class 3R at only 32 lumens is chief among them.  The flicker I also consider to be a fatal problem for a consumer product but this perhaps could be solved by going to a higher refresh rate (which would require a much faster scanning mirror).   The power consumption is far too high for embedding into small portable products.

And then we come back to the issues with the “use model” that still exists with Pico Projectors (see my discussion from way back in 2011 about this).

On a final note, I know that Laser Beam Scanning has a very dedicated following with some people that vigorously defend it.   I will be providing test patterns and other information so people can duplicate my experiments and verify my results.   I am more than happy to discuss the technology and respond to dissenting opinions, but I won’t tolerate rude comments or personal attack in the discussion.

Addendum — Test Patterns

Below are some test patterns stored in lossless PNG format to try out on the Celluon or other 720p projector to see for yourself.

Right-Click on the given pattern download the original full size pattern. Note, they should be view at “100%” if not on a 720p monitor and should totally fill the screen on 720p projector.

The first one below is a resolution test with 9 “zone patterns” has well as sets of 1 pixel wide black and white horizontal and vertical lines.

interlace res-chart-720P G100A


Simple horizontal gray ramp.  This is totally neutral gray from 0 to 255.Horz 0 to 255 gray ramp

Below may look dark gray or even black but it a totally flat R=B=G=16 everyone (a flay gray of 16/255).   See how it looks on the Celluon.

gray 16


Desperately Seeking the Next Big Thing – Head Mounted Displays (HMDs) — Part 1

Untitled-2With Microsoft’s big announcement of HoloLens and spending a reported $150 million just for HMD IP from the small Osterhout Design Group, reports of Facebook spending about $2 billion for Oculus Rift, and the mega publicity surrounding Google Glass and the hundreds of millions they have spent, Head Mounted Displays (HMD) are certainly making big news these days.

Most of the articles I have seen pretty much just parrot the company press releases and hype up these as being the next big thing.   Many of the articles have, to say the least, dubious technical content and at worst give misinformation.   My goal is to analyze the technology and much of what I am seeing and hearing does not add up.

The question is whether these are lab experiments with big budgets and companies jumping the gun that are chasing each other or whether HMDs really are going to be big in terms of everyone using them?    Or are the companies just running scared that they might miss the next big thing after cell phones and tablets.   Will they reach numbers rivaling cell phone (or at least a significant fraction)?    Or perhaps is there a “consolation prize market” which for HMDs would be to take significant share of the game market?

Let me get this out-of-the-way:  Yes, I know there is a lot of big money and smart people working on the problem.   The question is whether the problem is bigger than what is solvable?  I know I will hear from all the people with 20/20 hindsight all the successful analogies (often citing Apple) but for every success there many more that failed to catch on in a big way or had minor success and then dived.   As an example consider the investment in artificial intelligence (AI) and related computing in the 1980’s and the Intel iAPX 432 (once upon a time Intel was betting the farm on the 432 to be replacement for the 8086 until the IBM PC took off).    More recently and more directly related, 3-D TV has largely failed.  My point here is that big companies and lots of smart people make the wrong call on future markets all the time; sometimes the problems is bigger than all the smart people and money can solve.

Let me be clear, I am not talking about HMDs used in niche/dedicated markets.  I definitely see uses for HMDs applications where hands-free use is a definite.  A classic example is military applications where a soldier has to keep his hands free, is already wearing a helmet that messes up their hair and they don’t care what they look like, and they spend many hours in training.   There are also uses for HMD in the medical field for doctors as a visual aid and for helping people with impaired vision.  What I am talking about is whether we are on the verge of mass adoption.

Pardon me for being a bit skeptical, but on the technical side I still see some tremendous obstacles to HMD.    As I pointed out on this blog soon after Google Glass was announced HMDs have a very long history of not living up to expectations.

I personally started working on a HMD in 1998 and learned about many of the issues and problems associated with them.    There are the obvious measurable issues like size, weight, fit/comfort and can you wear them with your glasses, display resolution, brightness, ruggedness, storage, and battery life.   Then there are what I call the “social issues” like how geeky it looks, does it mess up a person’s hair, and taking video (a particularly hot topic with Google Glass).   But perhaps the most insidious problems are what I lump into the “user interface” category which include input/control, distraction/safety, nausea/disorientation, and what I loosely refer to “as it just doesn’t work right.”   These issues only just touch on what I sometime joking refer to as “the 101 problems with HMDs.”

A lot is made of the display device itself, be it a transmissive LCD, liquid crystal on silicon (LCOS), OLED, or TI’s DLP.    I have about 16 years of history working on display devices, particularly LCOS, and I know the pro’s and con’s on each one in some detail.   But as it turns out, the display device and its performance is among the least of the issues with HMDs, I had a very good LCOS device way back in 1998.   As with icebergs, the biggest problems are the ones below the surface.

This first article is just to set up the series.  My plan is to go into the various aspects and issue with HMDs trying to be as objective as I can with a bit of technical analysis.    My next article will be on the subject of “One eye, two eyes, transparent or not.”

Sony and Sumitomo

Sorry for being away from the blog so long.  I had two big “consulting gigs” come in one right after the other and I have been working virtually non-stop for the last 6 weeks.  There has been a lot of news come in that period in the area of displays and lasers and I will try and get caught up on some of it.

Today I would like to talk about Sony and Sumitomo announcement of a 530nm 100mW Green laser with 8% efficiency.  At least on the surface, this appears to be a big improvement what Soraa, Osram, and Nichia have announced to date.   But the big question is whether this really changes anything for pico projectors?

Semiconductor laser diode/True green laser emitting

Sumitomo and Sony 530nm Direct Green Laser Diode

Sony was much quieter than Soraa, OSRAM and Nichia but it certainly should have been expected since they developed blue lasers for blue ray (see for example from 2007 “Sony’s Blue Laser Diodes Down to $8 – PS3 and BD Player Price Cuts Soon?”).  Sumitomo had announce they were working on green laser materials back in 2010 but they were not known as a maker of laser diode end products and were thought to be a material supplier (to Sony as it turns out).

Another company to watch would be Opnext who is a leader in red lasers and announced a blue laser diode back in January 2011. All the green laser diode developments I know of came from “stretching” their blue laser developments to get green.

Certainly the Sony-Sumitomo device looks on the spec’s to be significantly better than other companies’ prior announcements with a 100mW, 530nm wavelength (huge improvement over the others), and 8% efficiency.  When you factor in the luminous efficiency at 530nm, they appear to have about double the lumens/Watt of any other green laser announcement I have seen.

Something else to consider, Sony has long been a manufacture of LCOS devices so I would suspect (I have no inside knowledge) that Sony would be looking to couple this laser with their LCOS developments.  They also have the ability to make some very small pixels from their in high resolution LCOS devices.  But the question is whether they and support field sequential color which it necessary for making small embeddable devices.  It should be noted that Sony has a line of  embedded pico projectors in video cameras that use TI’s DLP®

With all this activity and the seeming much improved spec’s from Sony-Sumitomo does this change everything and will laser projectors soon be everywhere?  Unfortunately, I don’t see this as changing things much, at least in the next year few years.

Now the bad news and just based on what they have said.  A 100mW 530nm green laser only supports about a 20 lumen projector which is pretty dim except for a pretty dark room or a very small image. A projector using an 8% WPE green laser probably does not have net an efficiency advantage (after factoring in all the pro’s and con’s) over a good LED projector with at 20 lumens.  While this might have been an interesting product a couple of years ago, the market has mostly moved on to higher lumen projectors.

And then we have to some questions that were not in the release.  Such as how far away is the Sony-Sumitomo green laser diode is from being a product and how much will it cost. Today a green LED to support a 20 lumen projector probably costs about $2. I think there is a serious question as to whether a ~20 lumen project has a value proposition today even if the lasers were inexpensive by the time you factor in the rest of the projector cost.

My bottom line is that it looks like Sony and Sumitomo have made some great technical progress, but it is does not appear to be enough to have a seriously competitive volume product in the market any time soon.    Anyway, that is the way I see it,


Soothsayer 7: Microvision’s Obfuscations Causing a Buzzing Sound

Microvision continues to make thinly veiled accusations against this blog in their May 9th, 2012 Company Displayground Blog (quoting directly with my bold emphasis added):

Our shareholders are following the topic of direct green lasers with avid interest and we get a lot of questions from them on price and availability. They have ridden the green laser wave with MicroVision and are understandably anxious for their investment and patience to pay off. There is another group of MicroVision watchers that take an active interest in direct green lasers and for that matter, all things MicroVision and have quite a bit to say. We welcome such interest as we are really proud of what our patented solution can do and the advancements we have made with the PicoP Gen2 display technology. But it does get tiring to have an open mic of misinformation from parties who only seem to have an interest in not seeing Microvision succeed. We try and ignore this contingent just like the best thing to do when a fly is buzzing around your head is to ignore it. Eventually the fly finds something or someone else to buzz around and the problem resolves itself.

Like most things Microvision writes they raise more questions than they answer.  For example, who is this “group” of watchers that “ have quite a bit to say” about green lasers?  As far as I know, this is the only blog regularly writing about green lasers for small projectors.   I guess they feel like I have them surrounded :-).   I would suggest that the real reason they cannot ignore the “buzzing sound” is that is goes contrary to Microvision’s attempts at obfuscation and eventually their investors and analysts ask questions.

I take the most interest went key specs are missing or when states what is at best a half-truth.  From what I read, Microvision obfuscates, uses straw-men, half-truths,  give meaningless ratios of improvements, and state goals/expectations as if they have been met.  They could put this all to rest if they could be specific about what they consider “misinformation” and give direct clear answers.  

$200 Green Laser Clarification:

Microvision’s blog when on to clarify(?) what Microvision’s Lance Even’s was saying green lasers costing nearly $200 that I address in my April 30th blog.  Quoting directly from the Microvision Blog:

The price of direct green lasers is understandably a topic of speculation since the manufacturers of the diodes have not publicly discussed pricing or even the exact timing of commercial availability. We cannot reveal specifics around these issues, but we can and have stated that we expect the prices of direct green lasers to be significantly less than synthetic green lasers which have cost nearly $200.

Microvision, apparently in response to my blog on the “nearly $200” price of DGL clarified that Mr. Evan’s $200 remark was in reference to the synthetic green lasers.   But note it is only an “expectation” (as in some time in the future) that the prices will be lower.

It is also interesting that Microvision is admitting publicly that the lasers were costing them nearly $200 (or maybe more at some point).  You have to wonder why they went to market with the ShowWX using a $200 laser for projector with only 10 to 15 lumens.  Can you imagine what investor reaction would have been back in 2009, 2010, or 2011 if they knew that Microvision was selling a supposedly high volume consumer product with a $200 laser in it?   My speculation is that unless they agreed to pay $200 for the lasers and buy a lot of them, that they would have had no way to build any product and if they couldn’t show (some pun intended) and that would make it impossible to raise money.   To keep investors on the hook, so to speak, they had to use obfuscation about the cost of lasers (some things never seem to change).  The losses on the ShowWx were essentially marketing expenses to raise money from the “shareholders” that were following the company back then.

They seem to have made the calculation that they needed to loose many millions of dollars on the ShowWx product line in order to keep the investor money flowing in.  Now that they consider those losses in the rear view mirror, they are admitting to them.   I wonder when they will come clean on the cost and specs of today’s direct green lasers.

More Half-Truths from Microvision

One more interesting set of half truths from Microvision’s blog:

We are confident that the manufacturers of the direct green lasers will be able to meet the volume requirements as the market demand for direct green lasers grows, and we expect price to fall accordingly.”

The first half-truth is that “manufacturers of the direct green lasers will be able to meet the volume requirements.”  Yes, this is true today, but only because the volumes will be very low.   Among the reasons is that the price of the lasers will be very high and that they are not currently designed into any high volume products.   Secondly, by laws of supply and demand, if the lasers are expensive few will be bought and thus they will meet the volume requirements.  Thirdly, the growth in the market could be very slow so it would be easy to meet what Microvision “expects.”    In short, Microvision like a politician, used a lot of words to give no real information.

What Microvision won’t admit, I suspect because that would be bad for raising money, is that the direct green laser has so far proven difficult to make due to the physics involved.    Certainly very smart and capable people are working on DGL, but they are not ready in the near future for the high volume consumer products.

Soothsayer 6: Microvision’s Lance Evans “Green lasers alone are $200 each now”

First, sorry for being away so long.  Some family and other matters took me a way and I fell out of the habit of posting.  I am going to try to have at least couple of posts up a week.

My “Soothsayer” series started back in December 2011 when Microvision released an 8-K a very trasparent response to this blog.  In Microvision’s Dec. 19th 2011 8-K they stated ““In the coming weeks we intend to provide a series of posts that discuss direct green lasers in more detail, as well as other business updates. Stay tuned!”

Well, it has been 19 weeks since Microvision’s 8K and there has been pretty much silence from them on “more details.”  Microvision has had plenty of opportunities to add “more details” in the last 5 months but has chosen not to.  They say a “slip in Washington is when you accidentally tell the truth” well maybe Microvision did that today.

In a way, Microvision finally broke the silence with an article today in an April 30th Technology Review article with Lance Evans (a director of business development at Microvision) stating, “Green lasers alone are $200 each now.” Remember this is probably for a green laser that supports on the order of a 15 lumen projector and has a wavelength that is too short (too blue) to be used in a typical projector and it not very efficient in terms of lumens per Watt. These are lasers that are a best useable in a car HUD display and not a batter powered cell phone or hand held projector.

Back in December 2011 Microvision’s 8K stated, “DGLs will be much cheaper than synthetic green lasers at introduction.”  How does this fit with DGL’s costing $200 today? 

The article does day that “Evans expects that costs should fall to a tenth of current levels by the end of this year,” but note the word “expects” is corporate speak for “believe, wish, hope, or dream” because you generally can’t hold them legally accountable for an “expectation.”  What other than a wish causes the direct green laser cost road map to drop from $200 now to one-tenth that cost or $20 in less than 7 months?  Are there people lined up to buy lasers first at $200, then $100, then $50 say to support a 15 lumen projector?  None of this makes any business sense.

Even if Mr. Evans “expectations” come true, and DGL drop by 10x in less than 7 months to $20 by the end of the year (really for 2013 production), is this really a viable business?   By comparison, there are 200 lumen LED base projectors on the market today and the cost of the red, green, and blue LEDs combined cost less than $20 today.   For a 15 lumen LED projector today, the LEDs are more like $3 for the RGB set.  For a pico projector to make it into a cell phone, the cost to the cell phone maker of the whole projector including electronics has to be on the order of $25 or less (just ask any cell phone maker, I have asked many).  You can even come close with even a $10 DGL, no less 20, when you factor in the cost of everything it takes to make a projector including optics and electronics.

I’m a long term believer that eventually all projectors and in fact a vast number of other products will be using lasers.   It is just going to take more than 2 year for the brilliant people at the laser manufactures to figure out how to make the direct green lasers at a cost point that will lead to mass adoption.

Soothsayer 5: Thanks for the “Shout Out” on the Microvision Conference Call!

It’s nice to know that a CEO of a public traded company is following my blog.   On today’s Microvision Conference Call (available for a few days) at 34:16 in the call, Microvision CEO, Alexander Tokman, in his closing remarks gave a “shout out” of sorts with,  “The direct green laser is becoming a reality this year and not 2014 as some led you to believe.

As anyone that has followed Microvision or my blog and my comments on direct green lasers the last few months should know, by “some” he means “me.”   First, he has mischaracterized what what has been written.    What I have written is that direct green lasers will not be practical for high volume applications until 2014 or beyond.

As I wrote Microvision’s “Soothsayer(?)” for their “Number One Question” in  response to me in Microvision 8K’s “false soothsayer” comments:

The real question is whether these lasers will be available at a price point, with a wavelength, and an efficiency that is practical.   I don’t doubt that most if not all the companies will be in production with a green laser in 2012, but what constitutes “mass production” is a different matter.   Nichia already has a 510nm green laser in production, for example, and it might be possible to build a heads up display for an automobile with it (albeit a bit expensive for the purpose), but that is clearly impractical in terms of wavelength, efficiency, and cost for building a high volume battery powered projector.   I also question whether they will be bright enough for a volume product other than a HUD.

Instead of addressing the real issues, Microvision has seen fit to play silly word games with the definition of word “commercial.”   “Commercial” simply means that companies will sell a product with a given spec.  It does not mean the that product, in this case a Direct Green Laser will meet the cost and performance requirements for a high volume application.  The reality is that the “commercial” direct green lasers are going to be available in 2012 (and 2013) are going to be way too expensive and with key performance limitations  for any kind of significant volume consumer products.

Now lets look at the math in Microvision’s timeline.  At 15:50 into the conference call Alexander Tokman talks about their commercialization timeline for a consumer product.    He said they hope to have a company committed by “mid year 2012” and that companies will generally take “6 to 18 months” to develop a product.   If you follow Microvision at all, you will note that Mr. Tokman timelines are usually wildly optimistic, but just taken him at his word with a “start” in mid 2012 and more realistically 12 to 18 months to get a product designed and ready for production adds up to products STARTING to be manufactured (not even high volume) in late 2013 to mid 2014 if (and this is a big if) everything goes according to Mr. Tokman’s hopes.

But given Mr. Tokman’s history of over optimism, this would seem to say that he is really talking 2014 or later; oh but wait, he said in the conference call that it was “not 2014 as some led you to believe.”     So which does his mean?

Soothsayer 4: Questions for Microvision’s Conference Call

I have been traveling for most of the last 2 weeks with a number of business meetings.   I thought I would get a quick blog out today ahead of Microvision’s  investor conference call on Monday Feb 27th (tomorrow as I write this).  I’ve listen to a few Microvision conference calls in the past and they usually say they have made great progress to some vague “goals” and then get a few softball/easy questions from the “financial analysts” that are allowed to ask questions and then quickly end the call.   You can listen to if “live” at 8:30AM Easter (5:30AM Pacific) or for a few days recorded at

It does not take some deep dark secret (i.e. confidential) information to figure out that laser beam steering ala Microvision has serious problems.   It just takes some engineering and business knowledge.  Below are a few questions I would like to see asked along with some information.

Microvision “720p” Optics and Driver Board

1) Isn’t the combination of the optics and drive electronics for Microvision’s 720p (see picture)  too large to be embedded into any major brand cell phone?    Right now you have 2 large ASICs and an FPGA to control the lasers and the mirror where the competition has only 1 much smaller ASIC.    According to the technical specifications this optics and electronics module is 35mm × 65mm × 6 .1 mm; how small do you have to get the module to meet the requirements of the major cell phone companies and when will you meet this requirement?

2) According to your technical specifications for the new 720p module, at “27% video” the power dissipation is “approximately 2 Watts.”   If this is 27% of 15 lumens (or even 25 lumens), it would suggest that at full brightness the power dissipation is on the order of 4 to 5 Watts.   You have stated in the past that the goal to meet the cell phone requirements about 1 Watt.   This would seem to be much worst power dissipation than the competing technologies.  How is any cell phone company going to embedded something like this that consumes so much power?     How long do you expect to take to get the power dissipation for the projector module down to your stated goal of about 1 Watt?

3)  According to your technical specifications for the new 720p module, at 25 lumens the module is a class 3R laser product and at 15 lumens it is class 2.   A) at what lumens between 15 and 25 does the product cross over into class 3R?  B) Isn’t even laser safety class 2 a serious problem for consumer product including cell phone companies?   C) What are the issues with trying to sell a class 3R product in the market, particularly when the competing technologies such as DLP and LCOS don’t have this issue?

4)  In your December 19th 2011 8K you stated“So what do I mean by “commercial version” direct green laser? It’s a laser that has passed through intense qualification by the component manufacturer to insure that it meets all of its intended performance specifications, with confirmed reliability and manufacturability necessary for mass production.”  But commercialization only means that they will be available for sale at some price, and it says nothing about them being viable for making profitable product.  Doesn’t all this talk about the definition of “commercial” just avoid the real issue of whether the lasers you need for laser beam steering will be PRACTICAL in terms of cost, power efficiency, lifetime, and wavelength (color) in 2012 and 2013 for embedded products like cell phones?

5)  The blog KGOnTech has posted several articles stating the laser beam scanning process will result in lower than your claimed 720p resolution.  Can you actually demonstrate that you can actually fully resolve a 1280 by 720 pixel test pattern?

6)  Lately you seem to have put a lot on emphasis on automotive heads up displays (HUD).    The power and size requirements are much more relaxed for this market.    Is this in some ways an admission that the lasers are not going to be ready for any embedded products in the near future.    

7)  Realistically, how large is the market going to be for an after market automotive HUD?   Are the laser cost, availability, brightness, and other specification acceptable today for the automotive market?

Please feel free to add questions or ask me to clarify my questions in the comments.


Answering Questions on Laser with LCOS and LBS

Syndiant 720p LCOS Panel

I got asked a series of questions by reader “me_wwwing” after the article Laser with LCOS is Focus Free — Yes Really! that I am answering in this post because I thought they would be of general interest.  I did have to edit a few of the questions for clarity but tried to keep the intent as best I could and I have re-ordered the questions to put what I think are the more interesting questions first.   For background for the reader I need to add that from prior questions and comments, I know me_wwwing to be a fan of Microvision’s laser beam scanning (LBS) so that may color some of the questions and the answers.

Q1. Does Syndiant need to use the same lasers as MVIS [Microvision laser beam scanning (LBS)]?

The simple answer is that LCOS panels can use any of the lasers that LBS can use and can use lasers that LBS cannot use.   LBS puts constraints on both Diode Pump Solid State Lasers (DPSS also known as “synthetic” or “frequency doubled) and for direct diode lasers (DGL).

Answer Part 1: DPSS Green Lasers

First, Syndiant makes the LCOS microdisplays and not the entire optical engine.     A panel (LCOS or DLP) optical engine has a wider selection of lasers that it can use both for direct green lasers as well as DPSS green lasers.   So the quick answer is that it can use any of the lasers that a LBS system can use plus it can use laser types and variation that LBS cannot use.

With DPSS green lasers, panels could use the less expensive to make and much more electrically efficient (generally about 2X the efficiency) slower switching lasers.  The slower switching frequency doubled lasers are capable of greater than 12% wall plug efficiency (WPE) with the desirable 532nm wavelength green.   About the best the fast switching frequency double green lasers ever got to was about 6% WPE.

The slower switching DPSS greens are capable of going to very high brightness; they can be over 10 times brighter than today’s Direct Green Diode Lasers (DGL).   Their electrical to lumen efficiency is over 3X the best DGLs today.   And their cost is lower than DGLs.   But the drawbacks to DPSS greens include the size and the small spectral bandwidth that causes higher speckle.

Answer Part 2: Direct Green Diode Lasers (DGL)

It turns out that there are different kinds of direct-diode lasers as well.  Most notably there are “single mode” and “multi-mode” lasers.

LCOS or DLP can use either the single-mode or multi-mode lasers, but lasers LBS can only use single-mode lasers.   Multi-mode lasers change wavelength, phase, and/or optical polarity somewhat randomly.  The rate of mode changing would look like noise in a LBS scanning process so it is unusable in an LBS system, but in a panel (LCOS or DLP) system the hopping simply gets average out as it is faster than the eye can detect.

Since changing wavelength and phase reduces speckle, multimode lasers have less speckle.  It turns out that lasers naturally want to mode hop, so it is easier (cheaper) to make multimode lasers, multimode lasers are more electrically efficient and multi-mode lasers can be made much brighter/more powerful (in fact, as they make the laser cavity bigger to make lasers more powerful it is hard to keep them from mode hopping).  So panel based projectors have a significant advantage in being able to use multi-mode lasers.

Historically, traditional laser uses such as telecom and interferometry, needed single mode lasers.   But the same coherent light for these applications is what causes speckle, so for panel based projectors you want “poor quality” lasers with less coherency and thus speckle.

Q2. How big is Syndiant Controller?

The Syndiant’s 720p ASIC is currently 9mm X 9mm in its current package, but could be put in a significantly smaller package by reducing the pin count for an embedded cell phone.  The current package has a lot of extra pins for supporting a mix of applications that make it bigger.

Q3. What are the dimensions of Syndiant’s PCB?  The new one or the old one to have a starting point.

Syndiant sells the panel and the driver ASIC and not a PCB per say.  Single SYA1231 ASIC for their 720p is currently 9mm x 9mm includes frame buffer memory and ARM CPU and can be put in a smaller package for embedded applications.    So there really isn’t much in the way of board space for the new Syndiant 720p controller.  Basically, it is just one small chip 9mm X 9mm chip and not a “PCB” per say.

Syndiant’s single small ASIC compares extremely favorably to the Microvision 720p board which has 2 custom ASICS (one about ~11mm x 11mm and the other ~10mm x 10mm)  and an Altera FPGA (~6mm x 6mm)  on it.  There is also a 4th I.C. on their board which is an Intersil laser driver (5mm x 5mm).   The  picture below is from with my notes added it:

Microvision "720p" Optics and Driver Board

Totalling up the area of Microvision’s two ASICs and FGPA, Syndiant’s current control ASIC takes about 1/3rd the area and 1/3rd the ICs of Microvision’s 3 chip controller.   Also just looking at all the power conversion circuitry required in the Microvision “720p” board suggests that it needs a lot of different voltages with some significant power requirements and all this adds cost, board space, and power.

Q4. What size diagonal lens (encased) does Syndiant’s displays need to cover the diagonal of the display?  A length too would be nice. old specs are ok to start with [assuming laser illumination]

The diagonal of the “active display” of the older SYL2010 was 0.21”.  It had a 5.4 micron (10-6 meter)  pixel such that an 800 pixel high display was 4.3mm.   The lens would need to be a bit thicker than this diagonal.  For a small high volume product the lens would be cut to a more rectangular than circular shape to reduce height.   So the lens could be about 6 mm thick.   The SSTDC SEE100 prototype engine  engine’s lens with its barrel was non-optimized (circular) and was about 8mm thick and 8mm long.  An optimize rectangular-cut lens could have been about 5mm tall.

There is nothing keeping LCOS with laser illumination from going below 5 micron pitch (they will eventually get to around 3 micron and perhaps less) for its pixels.   At about 5 microns the active display for a 720p would be about 3.6mm tall.  A rectangular cut lens would then be about 4.5mm to 5mm tall or a round lens would be about 7mm tall.

Q5. Does the dichroic color combiner lens need to cover the surface of the Vibrating Despeckle unit [the answer addresses the broader question of the light combining system for LCOS and LBS]?

No, the light is not significantly spread out before the dichroic color combiners in an LCOS system.  Also the alignment of the dichroic mirrors/filters and the lasers is non-critical in an LCOS or DLP optical engine.

In should note, however that the alignment of the lasers and the dichroic combiners is very critical in an LBS design.  You should note in this teardown picture (picture taken from a laserpointerforums) that I have labeled the two ball shaped optics (pointed to in magenta) used to aligned the red and blue lasers and then glued into place.   The need to critically align the lasers adds cost and quality issues into to the manufacturing process.

Microvision ShowWX (WVGA) Optics


Q6. What is the power to run the PCB and the light engine on a Syndiant’s Displays? (SVGA and WVGA).

That really is a complex and involved question and depends on a lot of factors including the optical engine design and the target brightness.  I am also assuming that this is with LED illumination.   With LEDs the lumens per Watt of power tends to go down as the projector gets brighter, that is one of the advantages with lasers, namely that efficiency does not go down with power. 

It is helpful to break the power into two part, the panel and controller electronics and then the illumination and optics.   For low lumen (less than 30 lumen) projectors, the power of the display and its control is a significant part of the overall power (and less so at higher brightnesses).

The Syndiant LCOS display and ASIC for the WVGA or SVGA will usually consumed about 0.4W.   Due to a number of design improvements, Syndiant’s 720p panel and ASIC consume less power while have a higher color field rate and better light throughput than the older WVGA and SVGA devices while having about 3X the pixels.

In the low lumen area of 10 to 15 lumens with a small, 0.21” WVGA or SVGA panel optical companies were able to get about 7 to 10 lumens per LED Watt.    With some power conversion overhead and including the panel and ASIC this mean that you could get with LEDs about 12 to 15 lumens for 2W of power.  While this is still not good enough for the very high volume cell phone applications, it compares very favorably to the ShowWX which takes 4+ Watts for about 15 lumens.

With lasers the efficiency depends heavily on the lasers used and is dominated by the green laser efficiency which is pretty poor with today’s DGLs.   With today’s DGL efficiencies, LEDs will produce more lumens per Watt, but this will change in the future as lasers improve.   I fully expect to see eventually over 30 lumens per Watt with DGL and LCOS because today with the current DGL, they would be doing well to get 3 to 5 lumens per Watt .

Q7. What would be the lumen output from Syndiant’s displays using the new lasers that Microvision will use [this question was edited for clarity].

This is not a simple question as the spec’s on the lasers and how they can be driven have not been finalized.   I’m pretty sure the lasers that Microvision was using “lab prototype” lasers at CES that were being “over driven.”  The best I can answer right now is to give some insight into the lumens per watt that can be expected as the lasers are perfected.

To begin with, the optical throughput for a laser/LCOS engine should be in the 30% to 40% range where for LBS the optical throughput is reported to be in the 55% to 60% range.   But note, this is the part of the system were LBS looks best in terms of efficiency, but this does not tell the whole story.

Where LBS looses in terms of efficiency is in the drive and control of the laser and the MEM’s mirror.    The Microvision MEM’s mirror alone (not including the ASICs and FPGA’s) at WVGA has been reported to take about 0.4 Watts.   Syndiant’s new 720p LCOS Microdisplay and ASIC combined will take less than that.   Then you have all the power of the 2 ASIC’s and the FPGA that the Microvision 720p board requires.    So LCOS starts with a big lead in terms of power just in power of the display and control.

Then we have biggest power wasters for LBS, that of having to analog modulate the laser drive power.   First you have the fact that each pixel in the laser beam scanning process must be analog modulated at very high speed and high speed analog modulation wastes power.

Additionally, most people are not aware that the laser beam also has to be modulated due to the varying speed of the laser sweep.   If you think about it the laser beam horizontal sweep has to accelerate from zero to the maximum speed at the center of the screen and then decelerate to stop at the far side before returning.  To make a solid image appear uniform, the laser drive has to be constantly varying (for a “solid white” image the drive approximates a sine wave).  See such as the Microvision White Paper (a figure from which is copied below) and the excerpt (copied below) from the Microvision patent application”Apparatus and Method for Interpolating the Intensities of Scanned Pixels“:

From US Patent Application 20090213040

Q7. What is the power to run the PCB and the light engine on a Syndiant’s Displays? (SVGA and WVGA).

That really is a complex and involved question and depends on a lot of factors including the optical engine design and the target brightness.  I am also assuming that this is with LED illumination.   With LEDs the lumens per Watt of power tends to go down as the projector gets brighter, that is one of the advantages with lasers, namely that efficiency does not go down with power.

The LCOS display and ASIC for the WVGA or SVGA will usually consume less than ess than 0.4W.   Due to a number of design improvements, Syndiant’s 720p panel and ASIC consume less power while have a higher color field rate and better light throughput than the older WVGA and SVGA devices while having about 2X to 3X the pixels.

In the low lumen area of 10 to 15 lumens with a small, 0.21” WVGA or SVGA panel optical companies were able to get about 7 to 10 lumens per LED Watt.    With some power conversion overhead and including the panel and ASIC this mean that you could get with LEDs about 12 to 15 lumens for 2W of power.  While this is still not good enough for the very high volume cell phone applications, it compares very favorably to the ShowWX which takes 4+ Watts for about 15 lumens.

Q8. Which VGA display panel is best suited for the cell phone market?

I don’t know that there is a “best.”  Right now about the only reasonably high volume embedded panel is the color filter LCOS one by Himax that is used in cell phones for the India and China market.   The performance of these engines is too poor to be used in “first world” markets.   I think many of them are also less than VGA resolution.   They are typically about 5 to 10 lumens with pretty poor color and contrast and use very cheap but relatively large optics.

Personally, I don’t see a big “first world” need for a VGA or WVGA display.   Why bother projecting an image that lower in resolution than the cell phone’s display?   I think the big market will be to projector resolutions that are at least 720p

Q9. Does Syndiant plan on building the Light Engine?

I can’t comment on Syndiant’s future plans, but Syndiant’s business model has been to be a panel supplier.    There are very large number of good optical engine companies in the world so I don’t know why Syndiant would want to change.

Q10. Is Syndiant depending on someone else to make the Light Engine and Syndiant only sell the display panel?

Syndiant makes the panel and for use by many companies.   This allows different companies to make different products aimed at different markets.

Q11. Does Syndiant’s displays need a Vibrating Despeckle unit with DGLs?

It depends on the DGLs.  With the multimode DGLs you can drive them in such a way as to induce more mode-hopping to reduce speckle.   I would expect the there will not be despeckling required with volume production DGLs.

Q12. Does the light coming off the Vibrating Despeckle unit need to cover the homoginizer [a reference to the 3 year old SSTDC optical engine that used a vibrating despeckler]?

In the old SSTDC design with a vibrating despeckler, the light was partly spread before going to the despeckling mirror but not as large as the homoginizer.


CES 2012 Pico Projector Overview

As part of my marathon training, I ran 18 miles the Sunday before CES and it turned out to also be good practice for attending CES.   I’d estimate I averaged over 4 miles walking the floor and between venues (it was faster to walk the mile to the Venetian than take a bus at busy times of day) plus my morning 3 mile jog.   For this post, I’m going to give some quick highlights of what I saw about pico projectors at CES.   I plan on writing in more detail about some of these items in in the near future.

Over half of the show hours I was in private meetings that I can’t talk about, but I did get a chance to see and hear about a number of pico projector related activities that are public.   I can’t hope to compete with the many people that give you the quick and glossy news of CES that mostly just repeat the company talking points, but as you should come to expect from me, I will be doings some more in-depth analysis with an engineer’s eye of the products.

QP Optoelectronics introduced their “Lightpad” product at CES.   It interfaces to smartphones with an HDMI output and combines a keyboard, DLP WVGA (848×480 pixel) pico projector, rear projection screen, and battery that easily folds up into a thin and light form factor.

While it is not perfect yet, there is a lot to like about the basic concept and they said they got a lot of interest at CES.   It at least starts to address some of the issues with “use model” that I have written about earlier.  I am working on an article that talks about the good and bad points of this concept and where I see this type of product  going in the future.

Syndiant’s biggest news was their formal announcement of the SYL2271 720P 0.31” diagonal LCOS microdisplay and its accompanying SYA1231 ASIC.   Shown at left is an actual picture of the SYL2271 that has been pasted into some cute artwork.  The Syndiant had three SYL2271 720P projectors running in their private suite all showing 720p HD movie content.  All of the optical engines were very much “prototypes” with some optical quality issues and not near production ready.

Syndiant also jointly announced Viewlink’s new Vizcom™ Wi-Fi Cloud-Connected Near-Eye Visual Communication System.  The VizCom system includes a wearable heads-up display with integrated 720p video camera and an AndroidTM smart controller.  VizCom allows content to be streamed directly to the cloud via built-in Wi-Fi or by 3G/4G wireless smartphones, tablets or cellular hotspots. The Syndiant SYL2010 SVGA (800×600 pixel) panel acts as a camera viewfinder and as a display.  There was a working prototype of the display but not the overall product in Syndiant’s suite.   The optical quality of the prototype optics left something to be desired but the mechanical workings of the headset seemed to be very workable compared to other near eye products I have used.

Syndiant had a demo of a 160 lumen 3-D passive glasses pico projector that used two SYL2061’s with a single projection lens in a light engine designed by ASTRI.   The projector would either present 80 lumens to each eye in 3-D mode or 160 lumens to both eyes in 2-D mode.

A number of Syndiant pico projector products were filling about half of 3M’s booth at CES.   There were several more conventional pico projectors like the older MP160 and MP180 plus a new SYL2061 WSVGA (1024×600) based MP220 with 50 lumens.

Additionally 3M was showing a new “Camcorder Projector,” the CP40, which combines a handheld video camcorder with an SVGA pico projector.

Syndiant based products could also be found at AAXA’s and WSOT’s booths at CES and I expect some other places that I may have missed.  AAXA was demonstrating a new projector based on Syndiant SYL2061 panel.   WSOT has a dual panel WSVGA 3-D passive glasses projector similar to the one at Syndiant’s suite.   They also had a demonstration of prototype projector with a 4cc light engine based on Syndiant SYL2030 WVGA (854×480) device.

TI’s DLP certainly had by far the biggest presence of any of the pico projector display makers; although most of the newer products probably should be called “mini” rather than “pico” projectors.   There were a number products based around their WXGA (1280×800) 0.44” panel with products that were from 1.3-inches to over 2 inches thick.  These products were clearly aimed more at business professionals to put in their briefcases and had marketing spec’s of 200, 300, and some with 500 lumens (note these are often their “marketing lumens” which often are inflated by 1.2X to nearly 2X depending on the brand).

All of these WXGA projectors were really designed for wall plug rather than battery operation and have no internal batteries.  But Vivitek did find a way to make their battery powered by adding large external battery packs.   Essentially these battery packs have DC power cord to plug into the DC jack normally used by the AC wall plug power pack.

There could also be found a number of very similar looking WVGA (848×480) DLP pico projectors at the various booths around the show with light outputs ranging from about 30 lumens to as much as 80 lumens.  Most of these projectors include internal batteries.

DLP Diamond Pixel Arrangement

Both the WVGA and WXGA projectors use what is known as “Diamond Pixels” in which the DLP mirrors are rotated 45 degrees in a tile like arrangement show at the left.  This is done to reduce the thickness of the optics (a complex discussion for another day).

The re-sampling/scaling of the image from a normal square pixel grid to the diamond grid  does have a negative impact with high-resolution computer content.  Click on the thumbnail on the right to see the effects of the diamond pixel scaling on a high-resolution test pattern.

A notable exception to the bigger and brighter DLP projectors and much more of a “true” pico projector was used in Sony’s lineup of 4 camcorder models with pico projectors build into backs of the flip-out LCDs monitors.  These projectors used DLP’s 0.22” diagonal nHD (one-ninth 1080p or 640×360 pixels).   It seems to me to be a mismatch to combine a 1080i camcorder with a pico projector that has 1/9th the pixels.

I was told my multiple companies at CES that TI has a major campaign to get all the makers of LCOS pico projectors to carry at least one DLP based projector.  TI provided all kinds of support to get the projector companies to have at least one DLP product and to a large degree they succeeded with companies including 3M and AAXA showing DLP products along with their LCOS projectors.

Microvision "720P" (click on image)

Microvision was showing a new “so called 720p” multimedia projector at CES.  I say “so called 720p” because they would only demonstrate low resolution cartoon like video games on it.  I did ask them to put up a test pattern to show that they really could do 720p (1280×720) resolution but they politely refused.   My engineering instinct is that if someone is claiming HD resolution, they would be showing off HD content.   I also noticed that the 720p projector seems to be off whenever they were not demonstrating it to someone which suggests that there may be some laser lifetime and/or heating issues with the device.

The prototype media player projector was to me surprising large considering they have been claiming the whole PicoP® concept to be aimed at embedded products.  While the light engine optics itself is about 4cc, by the time you add all the electronics and a very large heat sink/heat spreader underneath the projection engine, about 25cc (56mm x 38mm x 12mm) within the media player are consumed (click on the picture above that shows some of the dimension).  Imagine how much bigger still it would be if had to add the cell phone engine and its LCD/OLED display to the package.  Compared to DLP and LCOS projection engines, there seems to be a large amount of electronics associated with LBS.

The same week as CES, Microvision put out flyer with set of partial spec’s on the PicoP engine itself (less any of the media player features).    To a degree, the spec sheet confirms some serious issues with the whole laser beam scanning (LBS) concept that Microvision uses.  The flyer says that at 15 lumens it will be a Class 2 laser product, but in a footnote it admits that the 25 lumen version would be “Class 3R” confirming what I (and others) have said for years about the issues with laser safety standards with LBS.  Note, the cell phone makers have told me that they wouldn’t put anything beyond Class 1 (considered totally eye safe) into a consumer cell phone and LBS type displays would support less than 1 lumen at Class 1; so even the Class 2 rating at 15 lumens I would consider to be a serious problem.

Another interesting indirect admission in the “spec” is that they consume “Approximately 2.0 Watts” at “27% video.”    It seems like a bad job of trying to hide a power problem.  It begs several questions, most obviously, what is the power consumption at some rated (measured) lumens.  If we assume it is for their 15 lumen projector and simply scale up we get over 7 Watts!   To get a realistic power consumption we have to know how “approximately” the power consumption number is and what it covers in the system.   As I wrote previously about the ShowWX power consumption, they seem to be a long way from their power “goals” to fit in an embedded product.

Another little tidbit from the “spec” is that it only has 16-bits per pixel (64K colors which means they have only 6 bits two primary colors and 5 bits of the third primary).  Most products today have at least 24-bits per pixel (8 bits each of red, green, and blue) = 16 Million colors.   This suggests some limitation in the ability to control the colors with their system.

I will have some more comments on the Microvision 720p as well as their 3-D and hand tracking demonstrations in an upcoming article.

Vuzix Holographic Optics

Vuzix was demonstrating an interesting technology for near eye heads up displays.  They have holograms embedded in a thin piece of plastic that can bend the output of a projector 90 degrees, translate and expand it, bend it back 90 degrees, and have it focused at infinity (so your eyes can stay on the real world).

I didn’t get the best picture of it on the above (it is kind of tricky and I didn’t have much time) but it is impressive how they can manipulate the light using hologram light guides.   While the image is in focus and would seem to be acceptable the intended purpose of a near eye HUD/augmented reality display, the image quality is not what you would want for say watching a movie.  Everything seems to have a “glow” to it which I suspect come from the contortions that are done to the light by the holograms.

That’s it for the “overview.”  Certainly my coverage of CES was spotty and if anything I didn’t give a lot of coverage to DLP relative to the number of products that were at the show.  If you have questions or want more details on some subject, please ask.

Cynic’s Guild to CES — Measuring Resolution

Center of ShowWX image -- Click for larger view

I don’t care how good you think your eyes are you can’t tell the resolution of display without a test pattern.  On the show floor and in their demo rooms, companies are going to pick videos and images that make their product look good and that often will mean avoiding test patterns like the plague.  In particular, those who are “fudging” on their resolution will avoid any test patterns.

More than once, a company has made a claim for “resolution” or “pixels” that won’t stand up to being measured.   For this blog entry, I’m going to demonstrate with pictures I took of test patterns on the ShowWX how Microvision’s Laser Beam Scanning falls seriously short of their claimed resolution of “WVGA” (848×480 pixels) and in addition has some pretty severe imaging artifacts caused by their non-linear, bi-directional, scanning process.

I would be particularly curious to see how Microvision’s demo of their 720P device holds up to being measured.  My guess is that they won’t let you test it, but it is worth asking (I don’t think they will let me try for some reason).  I know they have people reading this blog, so if they really think it will stand up to being measured, they could use my test patterns or similar ones.

At the end of this article I am going to give you as series of simple royalty free test patterns that you can download  (while not required, it would be nice to include attribution to this blog if you use the patterns).  You can verify my results or use them to measure the real resolution of Microvision’s WVGA, their claimed to be 720P demo projector, or any other pico projector.

Laser beam scanning (LBS) has a multitude of problems with the way a mirror scans; it is far from the simple process they want you to think.  Those familiar with the ShowWX know that it has “bowtie” distortion of the overall image, but what really hurts their effective resolution is that the scanning  process very poorly matches that of a normal computer or camera image.

Microvision's Bi-Directional and Interlaced Scanning

Fig. 4 from Microvision’s patent application 20110249020 gives some idea as to the problem as it diagrams the basics of the Microvision bi-directional scanning process.  The key thing you should notice is that it doesn’t look anything like simple raster scans through a square grid of pixels.  The Microvision scanning process follows two crisscrossing sine-wave-like patterns and the pixels of the original image have to be scaled/resample to the non regular beam scanning pattern.  The beam scanning doesn’t go everywhere the pixels need to be and in scaling the image to match the scanning process, significant resolution is lost.

The mirror does not sweep the laser beam in straight lines at a uniform speed.  It follows more of a curved path (thus curves in the patent application Fig. 4 and the bow-tie effect).   As the mirror scans the laser beam it is constantly speeding up or slows down which if left uncompensated, would change the width and brightness of a pixel.   But this is just the start of the problems with the scanning process.

A lot of people think that Microvision’s scanning process works sort of like an old raster scanned TV CRT but it doesn’t.   On a CRT, the magnetic deflection of the beam’s horizontal retrace is very fast so beam is only on in one direction and it “retraces” with the electron beam off.

But with Microvision’s MEMs mirror horizontal “retrace” is the same speed as its forward direction.  Therefore if they turned off the laser beam during retrace, the laser would have to be off over half the time and they would need 2X more powerful lasers.  So Microvision uses a “bi-directional scan” where the lasers are turned on in both directions.   In their patent application Fig. 4 above, I have colored each of the two scans, one in blue and the other in red to make it easier to follow them.  A single scan takes about 1/60th of a second and Microvision makes two sweeps each offset by a half a line.   It takes 1/30th of a second for both sweeps to complete (which also causes some very undesirable flicker on the outsides of the image where the blue and red scans don’t overlap).  The two sweeps are offset by half a line to create the crisscross effect seen in Fig. 4.

A key thing to notice is that in the middle of the two horizontal sweeps the blue and red sweeps cross, but on the outsides they don’t.   Also notice the spacing between lines of a given scan varies.  The lines are pinched together on the left and right sides (right after the retrace starts) while in the middle they are very far apart.  This makes for a tough mapping/scaling of the pixels and the net effect as the pictures will show is to make the left and right sided of the image blurry.

Below is a picture of a test pattern generated by the ShowWX.  When you click on the thumbnail you will get a very large image to see all the detail.  The test pattern has a series of 4 pairs of black and white horizontal or vertical lines.  If the ShowWx met its claimed resolution, you should see these 4 line-pairs distinctly everywhere in the image.   But what the picture shows is that even in the center of the screen there are problems which get worst at the left and right side of the image.  Quite literally, in some spots the resolution is about 1/4th (half vertical and half horizontal) that which is claimed (the 4 line-pairs blur into a mass).  You will notice that the vertical line pairs are blurry in most places.  One special feature I added to this pattern is some groups of 2 horizontal line pairs where the second set of line pairs is on the odd lines relative to the first line pairs; interestingly one set is blurrier than the other set of lines.

The picture was shot at 1/30th of a second and has a “roll bar” where only one of the two scans is present.

ShowWX Test Pattern to Measure Resolution

Another major problem is that a vertical lines all have to be scaled to fit the laser scanning and this process tends to blur all the vertical lines (some more than others).   Yet one more problem is that the red, green, and blue lasers are not perfectly aligned with respect to each other which means that the image for red, green, and blue are all scaled independently of each other.  This in turn causes a color “aliasing” or “twisted rope effect” on vertical lines (see red arrows in in the picture below from the center of the projected image).

To top it all off, there seems to be some quantizing effect in the Microvision scaling process.  This causes vertical lines to jump sideways about 1/2 a pixel every so often.

The problems with the various colors aliasing in the “white” test pattern, make it hard to see the scanning process.   Below I have included a “green only” pattern so you can more clearly see the effects of the scanning process in a single color.

Below, I have included a crops with some arrows pointing to some of the problems on the right side and center of the projected image.   One thing to notice is that different line-pairs are blurrier than others.

Even in the center things get blurry

Below is the whole image (click to see the higher resolution version)



Finally, I have included a number of test patterns including the ones I used withthe Microvision ShowWX in the example above.   The ShowWX ones were a bit special because I found the unusual odd/even issues with the scanning process.   I have created test pattern that are aimed at the common resolutions used by pico projectors today including WVGA (848×480), SVGA (800×600), WSVGA (1024×600), 720P (1280×720) and WXGA (1280×800).  They should be used at 100% = native resolution of the projector.

848x480 ShowWX Test Chart

848x480 ShowWX Green Test Image

848x480 Test Chart

1280x720 Test Chart

1280x800 Test Chart

800x600 Test Chart

1024x600 Test Chart

Appendix – How the test pattern images were shot

It is kind of tricky to shoot a sharp image of a laser projector.  When shooing an LED illuminated projector, if you want a sharp picture you can stop down (use a higher f-number) the camera’s lens and use a slow shutter speed (say 1/6th of a second) to take out any “roll-bars” from a scanning projector or color field effects from a field sequential color projector.   But with a laser projector if you stop down the lens you make the laser speckle worse and obscure the resolution effects.

The slowest ISO speed on the DSLRs I uses were ISO100.   I didn’t have a set of neutral density filters available so this limited the ability control the shutter speed while getting the proper exposure.  Through some trial and error I settled on f/2.8 for the aperture and a shutter speed of 1/30th of a second (to capture both scans) and then used ISO200 to get the proper exposure.  Since the camera was synchronized to the ShowWx, this mean there would be exactly 1 roll-bar in the image so I took a number of pictures to get the roll-bar in a least objectionable position.   I could have shot at ISO100 and 1/15th of a second but then I would get two faint roll-bars in two places, I decide that one roll-bar was better than two faint ones.

The image above were taken with Canon 50mm f/1.8 prime (non-zoom) lens with the camera mounted on a tripod with an infrared remote.   A prime lens was used to give a sharp image will little distortion and chroma aberration.  All the images of the test pattern were shot at f/2.8 to give some “sharpness gain” over the len’s wide open aperture but still a low enough f-number to limit speckle.

From observations, shooting at f/2.8 resulted in less speckle than I observed with my naked eye. The speckle you see is a function of the structure of the human eye including the f-number of your iris, the size of your retina, the size of the rods and cones in your eye, the surface of the retina.   When you take a picture of a laser projected image with a camera, all these factors are different.  About the best you can do is adjust the f-number of the camera to try an approximate what you see.  In a future article, I plan on talking about the physics of laser speckle.

A 3-stop or more neutral density filter combined with shooting at ISO100 (or less if the cameras supported it) would have allow me to shoot at a lower shutter speed and remove (average out) the roll-bar.  If the projector was much brighter, a neutral density filter would have been absolutely required.