Archive for January 27, 2012

Laser with LCOS is Focus Free — Yes Really!

Focus Free LCOS+Laser Projection (click for larger image)

Yes, when LCOS panels are used with lasers they can be “Focus Free.”   I have found that even very technical people have a hard time believing this as it goes against one’s everyday experience dealing with “normal” light and lenses.    People assume that the main function of a lens is to “focus light.”  After all, people are used to having to focus a camera lens or with a projector using lamps or LED light.

The optical physics of why it is focus free would take a long technical discussion, but it has to do with the laser light being effectively infinite f-number.  It is analogous to stopping a camera down to a high f-number where the depth of focus become very large.

Hopefully, “seeing is believing.”  I have uploaded a couple of still pictures (click on images for larger versions) and a short YouTube video demonstrating the focus free nature of the a Laseno Projector (sold in the U.S. as the AAXA L2).  This projector used a SYL2010 SVGA (800×600) LCOS plane with a 5.4 micron pixel pitch and 0.21″ diagonal.

For the top picture in this article, I projected the image the ceiling and some crown molding in my house.  This ceiling has lots of angle and different depths to it and with the crown molding in the way there is some obvious depth differences. Of course with the Laseno/AAXA L2 projector, there is no focusing necessary.

Projected at and angle to demonstrate focus free

Projected at and angle to demonstrate focus free (click on image)

For the picture on the left, I projected the image at a skewed angle from the side to cause a range of depths to be displayed.  The problem you have is that while the projected image is focus free, when the laser light hits the screen it looses it high f-number characteristics and thus the camera needs to focus.   By projecting the image on a flat piece of paper and shooting the picture straight onto the piece of paper I was able to focus the camera while demonstrating the focus free nature of the projector.

But perhaps the best way to demonstrate the focus free nature of a laser/LCOS projector is with a video.  I shot a short ~1 minute video where I mounted the projector on a little dolly and pulled it back away from the screen.  There was some shaking as I moved the projector so I stopped occasionally as I moved it it back so you could see it was still in focus.   I zoomed with the video camera in so you could see the detail in the video image.   Note that the camera’s exposures was locked/fixed on the starting frame, so as the image gets larger, it becomes darker by the ratio of the area so as the projector pull back the video gets a little dark.

I would recommend watching the video at 720p and in full screen to see how the focus is maintained.

Focus Free Video Demonstration

Other Information on the Images

The ~2 year old Laseno projector I used for these pictures has a fixed focus lens.   The image become well focused about 8″ from the projector to infinity.

The Laseno projection lens is not of high quality and you will see some serious chroma aberrations in picture as well as some spots having some blur due to the quality of the lens.  Additionally the projector has “100% offset” meaning that it projects through only the top half of the projection lens so that the projector will project upward from a flat surface without having a keystone effect.  Because of the offset projection, the image is best at the bottom of the image (which is from the center of the lens) at the chroma aberrations (color separation) become progressively worst toward the time.

You definitely will see laser speckle in the images.  The despeckle design was low cost and done over 3 years ago and it uses frequency doubled green lasers which inherently have a high amount of speckle.  Most people who have seen the AAXA L1/L2 “live and compared it to the ShowWX have said that the speckle with the Laseno/AAXA L1/L2  is less than that of Microvision’s ShowWX.

Exclusive: New Pictures of Projected Images by Syndiant’s 720p LCOS Panel

I asked my old company Syndiant if I could take some high-resolution photos of their new SYL2271 720P LCOS panel and they agreed.   Below are pictures I took with an 18 megapixel DSLR.  With some cropping due to the camera being 3:2 versus HD 16:9), there are about 13 camera pixels per for each pixel in the projected image).

To be fair, the optics Syndiant was using were clearly “prototype” and not specifically designed for Syndiant’s 720p panel.   In fact, the optics were designed for a larger 720p panel and thus using the smaller Syndiant SYL2271 was pushing the optics as evident from some of the chroma aberrations and the overall ability to sharply focus the image.   So these images should be worse that what will be seen in the final products.  Also the illumination of the panel in the prototype projector was not uniform which causes some color variation across the white test pattern.

Click on the images below to see the full images.  Note if you view it at less than 100% you may see aliasing due to scaling of the 1 pixel wide horizontal and vertical lines.  So make sure you are looking at it at 100% (you may have to click on the + magnifying cursor on your browser to do so).

If you are not used to seeing such large pictures of projected images you will see things that are not visible to the naked eye when viewing them “live.”  Effectively, it is like looking at the projected images with a magnifying glass.

Syndiant 720P Text Pattern Projected Image

Below is a picture I like because it has a lot of color, detail, and skin tones.

SYL2271 Projected Image of Elf

The picture below is one I took in York England.  If you look at the image at 100% in the left hand tower you can guy-wires holding up the flag pole and the spokes in Ferris Wheel behind the tower.  The clouds demonstrate the ability to do smooth shading

SYL2271 Projected York - Find Ferris Wheel Above Upper Left Tower

Below is the 720p resolution test pattern I used for the first image:1280x720 KGOnTech Test Chart

QP Lightpad™ And Future Observations

QP Optoelectronic’s Lightpad appears to me to be an interesting “transitional product” in the evolution the pico projector “use model”.    In this post I am going to comment on what I think they got right and what will need to be improved to make pico projectors more useful.

The Lightpad combines a rear projection screen, keyboard with touchpad, WVGA (848×480) DLP pico projector, and battery that folds up into a thin form factor.   In effect it turns a smart-phone with HDMI output into a netbook (except that is for the currently for a non-jail-broken iPhone which does allow “mirroring” of the phone’s display) .   The phone acts as the computer with all the software on it, but you now have a larger, easier to read screen and a reasonable size keyboard for typing.  The projector can also be flipped around in a front projection mode to give a larger on say a wall or screen in dark environments.

The Lightpad address one big issue I have with the typical pico projector shoot on the wall use model, namely that there is almost never a white wall, in the right place with low enough ambient lighting to be useful.  The “shoot on the wall” use model only seem to work in very contrived demos.   The Lightpad addresses this issue by having a built-in rear projection screen.

The rear projection screen, as opposed to say a sheet of white paper address a very important issue for pico projectors, namely giving sufficient contrast in typical room lighting.   As I discussed perviously about ambient light, even a dimly lit room has 1 to 2 lumens per square foot and a well-lit room has 30 to 60 lumens per square foot.  It turns out that you want at least 10 to 1 contrast for a reasonably easy to read text, so with a 10 lumen or even 30 lumen projector you can’t project a very big image with much contrast on a white screen.   A rear projection screen is designed to only accept light from a certain range of angles behind it and reject most of the random room light coming from everywhere else.  Because of this “ambient light rejection” a rear projection screen will result in higher contrast in the final image.  So the rear projection screen enables lower lumen pico projector to be very usable in brighter room light conditions.

The keyboard on the Lightpad makes typing easy and the touchpad in front seems to integrate well with the touch interface on the front of the keyboard.  Because the rear projection screen is lightweight plastic, it solves the weight and potential breakages issue of carrying around a large LCD screen.   I could definitely see this type of product being useful for the professional that doesn’t want to carry a laptop with them.  As big an advantage as any being that all the software and data on your smart-phone is available to you without needed to worry about sync’ing or buying a bunch of software.

While I like the concept and QP got many things right in terms of functionality, there are both some short, medium, and long-term improvements that will hopefully be made over time by QP Optoelectroncs and/or other companies.

Short Term (Easy) Improvements

The most obvious flaw, one in which QP says they are working on to improve, is the rear projection screen.  In particular, it has a “hotspot” where if you look at the projector straight it is very bright in the center.    The hotspot effect is show in the picture at the left (but please note a camera exaggerates the effect so it is not as bad as the picture shows but still present).

The next issue, somewhat evident in the picture at the top of this article, is the size and bulk of the cables.  Some of those in the picture are associated with power that will not be there in portable use, but still there are some long bulky cables and adapters between the smart phone and the Lightpad.   In my experience, the cables can often take up more space than the pico projector itself. I would make the cables much shorter, smaller, thinner, and they should easily store into the Lightpad.

Medium Term Improvements

With their announcement of the Lightpad, QP optoelectronics also announced that they are working on a 720p (1280×720 pixels) version.    This certainly would be welcome as many of the newer, more advanced, smart phones are supporting 720p and higher resolutions and one of the big reasons to project a bigger image is to be able to see more.   It really doesn’t make much sense to project a large image if it low in resolution.   Having higher resolution would enable more normal notebook like use for applications such as editing and viewing documents, working on presentations, internet browsing, and spreadsheets.

Long Term Improvements

While Lightpad is light and about the size of a pad of paper when closed, it still does not fit in your pocket.  So you are left to have something to carry around. The really big volume potential for pico projectors is in having something that fits in a normal pocket so it can be with you wherever you go.   Improvements in LEDs and laser light sources should significantly reduce the size of the projector and its battery, but then the issue of the rigid screen and the physical keyboard.

Today with 1 Watt, only about 7 to 10 lumens is possible with LEDs and LCOS or DLP including the light source and light modulator (currently laser beam steering is far behind needing about 3 Watts to give just 10 lumens).   Realistically with significant improvements direct diode lasers and incremental improvements in the light modulators, in a few years it should be possible to produce to about 30 lumens per Watt.    If we want an image that covers about half a square foot, about the area of a small laptop LCD, that means we could get to about 60 lumens per square foot.   If the ambient lighting is normal room lighting of 30 to 60 lumens a square foot then we would only have 2:1 or 1:1 contrast and a very washed out image.  So even with major improvements in pico projector technology we will need to look for a dark corner of the room or still want some form of light controlled screen.

To make the screen easily portable it should roll up into something about the length of a pocket pen (about 6 inches long) and less than 1-inch around (about the size of a white board marker).    Making rollable rear screens with good light control and uniform light spreading (avoiding hot spots) is not that easy as generally there needs to be things like a Fresnel lens which wants to be rigid.  3M has developed Vikuity™ rear projection plastic films  that don’t use Fresnel lenses but these are still meant for rigid installation on a glass or Plexiglas rigid surface.  Perhaps something like the Vikuity materials could be made rollable.

While rear projection screens are the obvious approach,  a perhaps better rollable screen approach would be to use a “wavelength selectable” (WS) front screen.   With a wavelength selectable screen, only specific wavelengths of light are reflected and the other absorbed.  Since normal room or sunlight is “broad spectrum” most of the ambient light is absorbed.  The WS coating could be made on thin rollable plastic.  Sony made a rigid form of WS screen called the ChromaVue™ back around 2005.   At the time Sony said that they could make a rollable version with the same technology but it never came to market.  ChromaVue screens were designed to work with fairly broad spectrum projectors using high pressure lamps with color filters.  Unfortunately, manufacturing costs and low volumes of the ChromaVue screens appears to have caused Sony to stoop making them several years ago.   The task of making a WS screen with narrow band LEDs or Lasers should be much easier so I would think that we will see the re-emergence of WS screens in the future.

Virtual Keyboards and Other Input

Inexpensive camera input should enable the elimination of the physical keyboard with the pico projector projecting the image of a keyboard.  The use of cameras for input is becoming commonplace today with devices such as the Microsoft Kinect™.  In fact, many people in the field expect that pico projectors and cameras will commonly be paired together in future application.

In the case of a rear screen projection one technique is to use infrared cameras (CMOS cameras naturally detect infrared) to sense when and where the screen is touched such as with the Microsoft Surface®.  One advantage of the rear screen infrared approach is that it is relatively easy to detect when the screen as been touched.

There are more issues with a front projecting virtual keyboard.   The first of which is that it become very desirable to project the keyboard at a shallow angle so that the project does not have to be so far away from the surface of a table.   The shallow angle also means that the keyboard will not be blocked as much by shadows cast by one’s hands.   The use of laser light in pico projectors will make short throw, shallow angle projection much easier to implement.

A bit of a technical challenge with front projection keyboards is to know when a key has been pressed versus a finger hovering over a key an there is a lot of work going on in this area.   With structured light (for Microsoft presentation on structured light click here)  and/or multiple cameras detecting finger pressing versus hovering is possible.   One can also expect some quicker input like Swype to be employed.


My expectation is that we will see the pico projector evolve from today’s shoot on the wall gimmick/toy to being a really useful product.    I think the QP Lightpad makes a good first step in the right direction.   It is much easier and with faster adoption rates to use already successful user interfaces and use models than to try and create new ones.     At the same time one needs to live within the physics of what is possible, such as how many lumens will be possible in the coming years for a pocket size device.   The technology for virtual keyboards and multi-touch displays is becoming very advanced and should not be a limiting factor.

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.


Cynics Guide to CES – Glossary of Terms

With CES just around the corner, I thought I would share my observations about viewing demos at CES (and elsewhere).  While the vast majority of products demonstrated at CES are in or are very near production, there are more than a few “technology demos” of things that will never see store shelves.  In between, there are products or concepts that are not yet ready for “prime time” that may have to gloss over a flaw or two (or more).

For those that demonstrate product at CES, the weeks leading up to the show can be a time of panic.  While your friends and neighbors are enjoying the holidays, you may be frantically trying to get your demos for the show to work.  Sometimes that last part you need is going to show up just before the show (or even at the show).  At some point it may become clear that is is easier to “fix the demo than fix the product.”

Below I have generated a glossy of terms I have created mostly related to display product demos but often have general applicability.  While there is some tong-in-cheek in these “definitions,” there is also a good bit of truth to them:

Marketing Physics – Technical information provided by a marketing or sales person that is not bound by the ordinary laws of physics.  Ignorance is bliss and to close a deal a marketing person’s favorite words are “sure it can do that.”

Demoware – Refers to a device that is not near being ready to be a product and has serious problems and the demo has been crafted to hide these problems.  It is easier to change the content of the demo and/or its environment than fix the product.   A well crafted demo will not display anything that will demonstrate the weaknesses of the device.

A Wizard of Oz (physical) – There is something in the demo that is being hidden (as in “pay no attention to that man behind the curtain” in the MGM film).   If a “portable product” is bolted to the table, it probably has wires going to other hardware.

A Wizard of Oz (visual) – Carefully controlling the lighting, image size, viewing location and/or visual content in order to hide what would be obvious defects.   Sometimes you are seeing a “magic show” that has little relationship to real world use.

Swimsuit Ratio – The amount of clothing on a female model used in a display is inversely proportional to the image quality of the display device itself.   For example if the image quality is so-so, then the model has a swimsuit, if the image quality is really poor, then the model may be nude/seminude.   If the image quality is great, then you show dull things like text patterns.

Flashbulb Demos – There are some demo products shown that have key components with lifetimes that are so short that that they will barely last the week of the show.   There are even cases of companies having to replace the demos on display every day of CES.  Another example of this would be a handheld device that consumes so much power that the batteries have to be changed often.   Demos that are only turn on when they are being watched usually have a power, heat, or lifetime problem.

Pixar-ized – The showing of only cartoons because the device can’t control color well and/or has low resolution.  People have very poor absolute color perception but tend to be are very sensitive to skin tones and know what looks right when viewing humans, but the human visual systems is very poor at judging whether the color is right in a cartoon.  Additionally it is very hard to tell resolution when viewing a cartoon.

Avatarization – If the display device doesn’t display colors accurately but you want to have human faces in the demo, then you use the characters from “Avatar.”

Stilliphobia – Fear of showing a still image because people will find artifacts.  Videos make catchier demos but they can also be used to keep the things moving so it is hard to see artifacts in the display.  A good demo of a display product should have a mix of stills, videos, and human flesh tones.

Dracula effect – Making lighting environment untypically dark or otherwise crafting the lighting to hide the fact that a projector is not very bright.   The average person doesn’t understand the huge dynamic range of the human eye.  By making the environment darker, the projector will seem much brighter.

Close-up effect – Using extreme close-up pictures gives the illusion of higher resolution.  If you take an extreme close-up picture of a person so you can see their pores, people will confuse the resolution of the display with the ability to see fine detail in the picture.

“Escaped from the lab” – This is the demonstration of a product concept that is highly impractical for any of a number of reasons including cost, lifetime/reliability, size, unrealistic setting (for example requires a special room that few could afford), and dangerous without skilled supervision.  Sometimes demos “escape from the lab” because a company’s management has sunk a lot of money into a project and a public demo is an attempt to prove to management that the concepts will at least one day appeal to consumers.