Archive for October 27, 2016

AR/MR Combiners Part 2 – Hololens

hololens-combiner-with-patent

Microsoft’s Hololens is perhaps the most most well known device using flat “waveguide” optics to “combine” the real world with computer graphics. Note there are no actual “holograms” anywhere in Hololens by the scientific definition.

At left is a picture from the Verge Teardown of a Hololens SDK engine and a from a US Patent Application 2016/0231568 I have added some red and green dots to the “waveguides” in the Verge picture to help you see their outlines.

diffraction grating is a type of Diffractive Optical Element (DOE) and has a series of very fine linear structures with a period/repeated spacing on the order of the wavelengths of light (as in extremely small). hololens-diffraction-gratingA diffraction grating acts like a lens/prism to bend the light and as an unwanted side effect the light also is split separated by wavelength (see top figure at left) as well has affecting the polarization of the light. If it were a simple grating, the light would symmetrically split the light in two directions (top figure at left) but as the patent points out if the structure is tilted then more of the light will go in the desired direction (bottom figure at left).   This is a very small structure (on the order of the wavelength of the light) must be formed on the surface of the flat waveguide.

Optical waveguides use the fact that once light enters glass or clear plastics at a certain angle or shallower, it is will totally reflect, what is known as Total Internal Reflection or TIR.  The TIR critical angle is around 45 degrees for the typical glass and plastics with their coatings used in optics.

hololens-patent-sideviewHololens use the diffraction grating (52 in Fig 3B above) to bend or “incouple” the light or the light so that it will TIR (see figure at right).   The light then TIR’s off of the flat surfaces around within the glass and hits off a triangular “fold zone” (in Fig. 3B above) which causes light to turn ~90 degrees down to the “exit zone” DOE (16 in Fig. 3B).  The exit zone DOE causes the angle of the light to be reduced so it will no longer TIR so it can exit the glass toward the eye.

Another function of the waveguides, particularly the exit waveguide 16 is to perform “pupil expansion” or slightly diffusing the light so that the image can be viewed from a wider angle.   Additionally, it is waveguide 16 that the user sees the real world through and invariably it has to have some negative effect from seeing the world through a slightly diffuse diffraction grating.

Hololens is far from the first to use DOE’s to enter and exit a flat waveguide (there are many examples) and they appear to have acquired the basic technology from Nokia’s efforts of about 10 years ago.   Other’s have used holographic optical elements (HOE) which perform similar functions to DOEs and still others have use more prismatic structure in the waveguides, but each of these alternatives solves some issues as the expense of others.

A big issue for the flat combiners I have seen to date has been chroma aberrations, the breaking up of white light into colors and out of focus and haze effects.   In bending the light at about 45 degrees is like going through a “prism” and the color separate, follow slightly different paths through the waveguide and are put back together by the exit grating.  The process is not perfect and thus there is some error/haze/blur that can be multiple pixels wide. Additionally as pointed out earlier, the user is invariably looking  at the real world through the structure meant to cause the light to exit the from the waveguide toward the eye and it has to have at least some negative effect.

There is a nice short 2013 article on flat combiners by (one author being a Google employee) that discusses some of the issues with various combiners including the Nokia one on which Hololens is base.  In particular they stated:

“The main problems of such architecture are the complexity of the master fabrication and mass replication as well as the small angular bandwidth (related to the resulting FOV). In order to mimic the holographic Bragg effect, sub-wavelength tilted structures with a high aspect ratio are needed, difficult to mass replicate for low cost volume production”  

Base on what I have heard from a couple of sources, the yield is indeed currently low and thus the manufacturing cost is high in making the Hololens combiner.   This may or may not be a solvable (in terms of meeting a consumer acceptable price) problem with volume production.

hololens-odg-comparisonWhile the Hololens combiner is a marvel of optical technology, one has to go back and try and understand why they wanted a thin flat combiner rather than say the vastly simpler (and less expensive maybe by over 10X) tilted flat combiner that say Osterhout Design Group (ODG), for example, is currently using.   Maybe it is for some planned greater advantage in the long term, but when you look at the current Hololens flat combiner, the size/width of the combiner would seem to have little effect on the overall size of the resulting device.  Interestingly, Microsoft has spent about $150 million in licensing fees to ODG.

Conclusions

Now step back and look at the size of the whole Hololens structure with the concentric bands going around the users head.  There is inner band to grip the user’s head while the electronics is held in the outer band.  There is a large nose bridge to distribute the weight on the persons nose and a big curve shield (usually dark tinted) in front of the combiner.  You have to ask, did the flat optical combiner make a difference?

I don’t know reasons/rational/advantages of why Hololens has gone with a vastly more complex combiner structure.   Clearly at the present, it does not give a significant (if any) size advantage.   It almost looks like they had this high tech combiner technology and decided to use it regardless (maybe it was the starting point of the whole program).

Microsoft is likely investing several billion dollars into Hololens. Google likely spent over $1 billion on the comparatively very simple Google Glass (not to mention their investment in Magic Leap). Closely realated, Facebook spent $2b to acquire Oculus Rift. Certainly big money is being thrown around, but is it being spent wisely?

Side Comments: No Holograms Anywhere to be Found

What Microsoft calls “Holograms” are the marketing name Microsoft has given to Mixed Reality (MR).   It is rather funny to see technical people that know better stumble around saying things like “holograms, but not really holograms, . . .”  Unfortunately due to the size and marketing clout of Microsoft others such as Metavision has started calling what they are doing “holograms” too (but this does not make is true).

Then again probably over 99% of what the public thinks are “holograms” are not.  Usually they are simple optical combiner effects cause by partial reflections off of glass or plastic.

Perhaps ironically, while Microsoft talks of holograms and the product as the “Hololens” there are as best I can find no holograms used even static ones that could have been used in the waveguide optics (they use diffraction gratings instead).

Also interestingly, the patent application is assigned to Microsoft Technology Licensing, LLC., a recently separated company from Microsoft Inc.  This would appear to be in anticipation of future patent licensing/litigation (see for example).

Next Time on Combiners

Next time on this subject, I plan on discussing Magic Leap the $1.4 Billion invested “startup” and what it looks like they may be doing.   I was originally planning on covering it with Hololens, but it became clear that it was too much to try and cover in one article.

AR/MR Optics for Combining Light for a See-Through Display (Part 1)

combiners-sample-cropIn general, people find the combining of an image with the real world somewhat magical; we see this with heads up displays (HUDs) as well as Augmented/Mixed Reality (AR/MR) headsets.   Unlike Starwars R2D2 projection into thin air which was pure movie magic (i.e. fake/impossible), light rays need something to bounce off to redirect them into a person’s eye from the image source.  We call this optical device that combines the computer image with the real world a “combiner.”

In effect, a combiner works like a partial mirror.  It reflects or redirects the display light to the eye while letting light through from the real world.  This is not, repeat not, a hologram which it is being mistakenly called by several companies today.  Over 99% people think or call “holograms” today are not, but rather simple optical combining (also known as the Pepper’s Ghost effect).

I’m only going to cover a few of the more popular/newer/more-interesting combiner examples.  For a more complete and more technical survey, I would highly recommend a presentation by Kessler Optics. My goal here is not to make anyone an optics expert but rather to gain insight into what companies are doing why.

With headsets, the display device(s) is too near for the human eye to focus and there are other issues such as making a big enough “pupil/eyebox” so the alignment of the display to the eye is not overly critical. With one exception (the Meta 2) there are separate optics  that move apparent focus point out (usually they try to put it in a person’s “far” vision as this is more comfortable when mixing with the real word”.  In the case of Magic Leap, they appear to be taking the focus issue to a new level with “light fields” that I plan to discuss the next article.

With combiners there is both the effect you want, i.e. redirecting the computer image into the person’s eye, with the potentially undesirable effects the combiner will cause in seeing through it to the real world.  A partial list of the issues includes:

  1. Dimming
  2. Distortion
  3. Double/ghost images
  4. Diffraction effects of color separation and blurring
  5. Seeing the edge of the combiner

In addition to the optical issues, the combiner adds weight, cost, and size.  Then there are aesthetic issues, particularly how they make the user’s eye look/or if they affect how others see the user’s eyes; humans are very sensitive to how other people’s eye look (see the EPSON BT-300 below as an example).

FOV and Combiner Size

There is a lot of desire to support a wide Field Of View (FOV) and for combiners a wide FOV means the combiner has to be big.  The wider the FOV and the farther the combiner is from the eye the bigger the combiner has to get (there is not way around this fact, it is a matter of physics).   One way companies “cheat” is to not support a person wearing their glasses at all (like Google Glass did).

The simple (not taking everything into effect) equation (in excel) to computer the minimum width of a combiner is =2*TAN(RADIANS(A1/2))*B1 where A1 is the FOV in degrees and and B1 is the distance to farthest part combiner.  Glasses are typically about 0.6 to 0.8 inches from the eye and the size of the glasses and the frames you want about 1.2 inches or more of eye relief. For a 40 degree wide FOV at 1.2 inches this translates to 0.9″, at 60 degrees 1.4″ and for 100 degrees it is 2.9″ which starts becoming impractical (typical lenses on glasses are about 2″ wide).

For, very wide FOV displays (over 100 degree), the combiner has to be so near your eye that supporting glasses becomes impossible. The formula above will let your try your own assumptions.

Popular/Recent Combiner Types (Part 1)

Below, I am going to go through the most common beam combiner options.  I’m going to start with the simpler/older combiner technologies and work my way to the “waveguide” beam splitters of some of the newest designs in Part 2.  I’m going to try and hit on the main types, but there are many big and small variations within a type

gg-combinerSolid Beam Splitter (Google Glass and Epson BT-300)

These are often used with a polarizing beam splitter polarized when using LCOS microdisplays, but they can also be simple mirrors.  They generally are small due to weight and cost issues such as with the Google Glass at left.  Due to their small size, the user will see the blurry edges of the beam splitter in their field of view which is considered highly undesirable.  bt-300Also as seen in the Epson BT-300 picture (at right), they can make a person’s eyes look strange.  As seen with both the Google Glass and Epson, they have been used with the projector engine(s) on the sides.

Google glass has only about a 13 degree FOV (and did not support using a person’s glasses) and about 1.21 arc-minutes/pixel angular resolution with is on the small end compared to most other headset displays.    The BT-300 about 23 degree (and has enough eye relief to supports most glasses) horizontally and has dual 1280×720 pixels per eye giving it a 1.1 arc-minutes/pixel angular resolution.  Clearly these are on the low end of what people are expecting in terms of FOV and the solid beam quickly becomes too large, heavy, and expensive at the FOV grows.  Interesting they are both are on the small end of their apparent pixel size.

meta-2-combiner-02bSpherical/Semi-Spherical Large Combiner (Meta 2)

While most of the AR/MR companies today are trying to make flatter combiners to support a wide FOV with small microdisplays for each eye, Meta has gone in the opposite direction with dual very large semi-spherical combiners with a single OLED flat panel to support an “almost 90 degree FOV”. Note in the picture of the Meta 2 device that there are essentially two hemispheres integrated together with a single large OLED flat panel above.

Meta 2 uses a 2560 by 1440 pixel display that is split between two eyes.  Allowing for some overlap there will be about 1200 pixel per eye to cover 90 degrees FOV resulting in a rather chunkylarge (similar to Oculus Rift) 4.5 arc-minutes/pixel which I find somewhat poor (a high resolution display would be closer to 1 a-m/pixel).

navdy-unitThe effect of the dual spherical combiners is to act as a magnifying mirror that also move the focus point out in space so the use can focus. The amount of magnification and the apparent focus point is a function of A) the distance from the display to the combiner, B) the distance from the eye to the combiner, and C) the curvature.   I’m pretty familiar with this optical arrangement since the optical design it did at Navdy had  similarly curved combiner, but because the distance from the display to the combiner and the eye to the combiner were so much more, the curvature was less (larger radius).

I wonder if their very low angular resolution was as a result of their design choice of the the large spherical combiner and the OLED display’s available that they could use.   To get the “focus” correct they would need a smaller (more curved) radius for the combiner which also increases the magnification and thus the big chunky pixels.  In theory they could swap out the display for something with higher resolution but it would take over doubling the horizontal resolution to have a decent angular resolution.

I would also be curious how well this large of a plastic combiner will keep its shape over time. It is a coated mirror and thus any minor perturbations are double.  Additionally and strain in the plastic (and there is always stress/strain in plasic) will cause polarization effect issues, say whenlink-ahmd viewing and LCD monitor through it.   It is interesting because it is so different, although the basic idea has been around for a number of years such as by a company called Link (see picture on the right).

Overall, Meta is bucking the trend toward smaller and lighter, and I find their angular resolution disappointing The image quality based on some on-line see-through videos (see for example this video) is reasonably good but you really can’t tell angular resolution from the video clips I have seen.  I do give them big props for showing REAL/TRUE video’s through they optics.

It should be noted that their system at $949 for a development kit is about 1/3 that of Hololens and the ODG R-7 with only 720p per eye but higher than the BT-300 at $750.   So at least on a relative basis, they look to be much more cost effective, if quite a bit larger.

odg-002-cropTilted Thin Flat or Slightly Curved (ODG)

With a wide FOV tilted combiner, the microdisplay and optics are locate above in a “brow” with the plate tilted (about 45 degrees) as shown at left on an Osterhout Design Group (ODG) model R-7 with 1280 by 720 pixel microdisplays per eye.   The R-7 has about a 37 degree FOV and a comparatively OK 1.7 arc-minutes/pixel angular resolution.

odg-rr-7-eyesTilted Plate combiners have the advantage of being the simplest and least expensive way to provide a large field of view while being relatively light weight.

The biggest drawback of the plate combiner is that it takes up a lot of volume/distance in front of the eye since the plate is tilted at about 45 degrees from front to back.  As the FOV gets bigger the volume/distance required also increase.
odg-horizons-50d-fovODG is now talking about a  next model called “Horizon” (early picture at left). Note in the picture at left how the Combiner (see red dots) has become much larger. They claim to have >50 degree FOV and with a 1920 x 1080 display per eyethis works out to an angular resolution of about 1.6 arc-minutes/pixel which is comparitively good.

Their combiner is bigger than absolutely necessary for the ~50 degree FOV.  Likely this is to get the edges of the combiner farther into a person’s peripheral vision to make them less noticeable.

The combiner is still tilted but it looks like it may have some curvature to it which will tend to act as a last stage of magnification and move the focus point out a bit.   The combiner in this picture is also darker than the one in the older R-7 combiner and may have additional coatings on it.

ODG has many years of experience and has done many different designs (for example, see this presentation on Linked-In).  They certainly know about the various forms of flat optical waveguides such as Microsoft’s Hololens is using that I am going to be talking about next time.  In fact,  that Microsoft’s licensed Patent from ODG for  about $150M US — see).

Today, flat or slightly curved thin combiners like ODG is using probably the best all around technology today in terms of size, weight, cost, and perhaps most importantly image quality.   Plate combiners don’t require the optical “gymnastics” and the level of technology and precision that the flat waveguides require.

Next time — High Tech Flat Waveguides

Flat waveguides using diffraction (DOE) and/or holographic optical elements (HOE) are what many think will be the future of combiners.  They certainly are the most technically sophisticated. They promise to make the optics thinner and lighter but the question is whether they have the optical quality and yield/cost to compete yet with simpler methods like what ODG is using on the R-7 and Horizon.

Microsoft and Magic Leap each are spending literally over $1B US each and both are going with some form of flat, thin waveguides. This is a subject to itself that I plan to cover next time.

 

Near Eye AR/VR and HUD Metrics For Resolution, FOV, Brightness, and Eyebox/Pupil

Image result for oculus riftI’m planning on following up on my earlier articles about AR/VR Head Mounted Displays
(HMD) that also relate to Heads Up Displays (HUD) with some more articles, but first I would like to get some basic Image result for hololenstechnical concepts out of the way.  It turns out that the metrics we care about for projectors while related don’t work for hud-renaultmeasuring HMD’s and HUDs.

I’m going to try and give some “working man’s” definitions rather than precise technical definitions.  I be giving a few some real world examples and calculations to show you some of the challenges.

Pixels versus Angular Resolution

Pixels are pretty well understood, at least with today’s displays that have physical pixels like LCDs, OLEDs, DLP, and LCOS.  Scanning displays like CRTs and laser beam scanning, generally have additional resolution losses due to imperfections in the scanning process and as my other articles have pointed out they have much lower resolution than the physical pixel devices.

When we get to HUDs and HMDs, we really want to consider the angular resolution, typically measured in “arc-minutes” which are 1/60th of a degree; simply put this is the angular size that a pixel covers from the viewing position. Consumers in general haven’t understood arc-minutes, and so many companies have in the past talked in terms of a certain size and resolution display viewed from a given distance; for example a 60-inch diagonal 1080P viewed at 6 feet, but since the size of the display, resolution and viewing distance are all variables its is hard to compare displays or what this even means with a near eye device.

A common “standard” for good resolution is 300 pixels per inch viewed at 12-inches (considered reading distance) which translates to about one-arc-minute per pixel.  People with very good vision can actually distinguish about twice this resolution or down to about 1/2 an arc-minute in their central vision, but for most purposes one-arc-minute is a reasonable goal.

One thing nice about the one-arc-minute per pixel goal is that the math is very simple.  Simply multiply the degrees in the FOV horizontally (or vertically) by 60 and you have the number of pixels required to meet the goal.  If you stray much below the goal, then you are into 1970’s era “chunky pixels”.

Field of View (FOV) and Resolution – Why 9,000 by 8100 pixels per eye are needed for a 150 degree horizontal FOV. 

As you probably know, the human eye’s retina has variable resolution.  The human eyes has roughly elliptical FOV of about 150 to 170 degrees horizontally by 135 to 150 degrees vertically, but the generally good discriminating FOV is only about 40 degree (+/-20 degrees) wide, with reasonably sharp vision, the macular, being about 17-20 degrees and the fovea with the very best resolution covers only about 3 degrees of the eye’s visual field.   The eye/brain processing is very complex, however, and the eye moves to aim the higher resolving part of the retina at a subject of interest; one would want the something on the order of the one-arc-minute goal in the central part of the display (and since having a variable resolution display would be a very complex matter, it end up being the goal for the whole display).

And going back to our 60″, 1080p display viewed from 6 feet, the pixel size in this example is ~1.16 arc-minutes and the horizontal field of view of view will be about 37 degrees or just about covering the generally good resolution part of the eye’s retina.

Image result for oculus rift

Image from Extreme Tech

Now lets consider the latest Oculus Rift VR display.  It spec’s 1200 x 1080 pixels with about a 94 horz. by 93 vertical FOV per eye or a very chunky ~4.7 arc-minutes per pixel; in terms of angular resolution is roughly like looking at a iPhone 6 or 7 from 5 feet away (or conversely like your iPhone pixels are 5X as big).   To get to the 1 arc-minute per pixel goal of say viewing today’s iPhones at reading distance (say you want to virtually simulate your iPhone), they would need a 5,640 by 5,580 display or a single OLED display with about 12,000 by 7,000 pixels (allowing for a gap between the eyes the optics)!!!  If they wanted to cover the 150 by 135 FOV, we are then talking 9,000 by 8,100 per eye or about a 20,000 by 9000 flat panel requirement.

Not as apparent but equally important is that the optical quality to support these types of resolutions would be if possible exceeding expensive.   You need extremely high precision optics to bring the image in focus from such short range.   You can forget about the lower cost and weight Fresnel optics (and issues with “God rays”) used in Oculus Rift.

We are into what I call “silly number territory” that will not be affordable for well beyond 10 years.  There are even questions if any know technology could achieve these resolutions in a size that could fit on a person’s head as there are a number of physical limits to the pixel size.

People in gaming are apparently living with this appallingly low (1970’s era TV game) angular resolution for games and videos (although the God rays can be very annoying based on the content), but clearly it not a replacement for a good high resolution display.

Now lets consider Microsoft’s Hololens, it most criticized issue is is smaller (relative to the VR headsets such as Oculus) FOV of about 30 by 17.5 degrees.  It has a 1268 by 720 pixel display per eye which translates into about 1.41 arc-minutes per pixel which while not horrible is short of the goal above.   If they had used 1920×1080 (full HD) microdisplay devices which are becoming available,  then they would have been very near the 1 arc-minute goal at this FOV.

Let’s understand here that it is not as simple as changing out the display, they will also have to upgrade the “light guide” that the use as an combiner to support the higher resolution.   Still this is all reasonably possible within the next few years.   Microsoft might even choose to grow the FOV to around 40 degrees horizontally rather and keep the lower angular resolution a 1080p display.  Most people will not seriously notice the 1.4X angular resolution different (but they will by about 2x).

Commentary on FOV

I know people want everything, but I really don’t understand the criticism of the FOV of Hololens.  What we can see here is a bit of “choose your poison.”  With existing affordable (or even not so affordable) technology you can’t support a wide field of view while simultaneously good angular resolution, it is simply not realistice.   One can imaging optics that would let you zoom between a wide FOV with lower angular resolution and a smaller FOV with higher angular resolution.  The control of this zooming function could perhaps be controlled by the content or feedback from the user’s eyes and/or brain activity.

Lumens versus Candelas/Meter2 (cd/m2 or nits)

With an HMD or HUD, what we care about is the light that reaches the eye.   In a typical front projector system, only an extremely small percentage of the light that goes out of the projector, reflects off the screen and makes it back to any person’s eye, the vast majority of the light goes to illuminating the room.   With a HMD or HUD all we care about is the light that makes it into the eye.

Projector lumens or luminous flux, simply put, are a measure of the total light output and for a projector is usually measure when outputting a solid white image.   To get the light that makes it to the eye we have to account for the light hits a screen, and then absorbed, scattered, and reflects back at an angle that will get back to the eye.  Only an exceeding small percentage (a small fraction of 1%) of the projected light will make it into the eye in a typical front projector setup.

With HMDs and HUDs we talk about brightness in terms candelas-per-Meter-Squared (cd/m2), also referred to as “nits” (while considered an obsolete term, it is still often used because it is easier to write and say).  Cd/m2 (or luminance) is measure of brightness in a given direction which tells us how bright the light appears to the eye looking in a particular direction.   For a good quick explanation of lumens, cd/m2 I would recommend a Compuphase article.

Image result for hololens

Hololens appears to be “luminosity challenged” (lacking in  cd/m2) and have resorted to putting sunglasses on outer shield even for indoor use.  The light blocking shield is clearly a crutch to make up for a lack of brightness in the display.   Even with the shield, it can’t compete with bright light outdoors which is 10 to 50 times brighter than a well lit indoor room.

This of course is not an issue for the VR headsets typified by Oculus Rift.  They totally block the outside light, but it is a serious issue for AR type headsets, people don’t normally wear sunglasses indoors.

Now lets consider a HUD display.  A common automotive spec for a HUD in sunlight is to have 15,000 cd/m2 whereas a typical smartphone is between 500 and 600 cd/m2 our about 1/30th the luminosity of what is needed.  When you are driving a car down the road, you may be driving in the direction of the sun so you need a very bright display in order to see it.

The way HUDs work, you have a “combiner” (which may be the car’s windshield) that combines the image being generated with the light from the real world.  A combiner typical only reflects about 20% to 30% of the light which means that the display before the combiner needs to have on the order of 30,000 to 50,000 cd/m2 to support the 15,000 cd/m2 as seen in the combiner.  When you consider that you smartphone or computer monitor only has about 400 to 600 cd/m2 , it gives you some idea of the optical tricks that must be played to get a display image that is bright enough.

phone-hudYou will see many “smartphone HUDs” that simply have a holder for a smarphone and combiner (semi-mirror) such as the one pictured at right on Amazon or on crowdfunding sites, but rest assured they will NOT work in bright sunlight and only marginal in typical daylight conditions. Even with combiners that block more than 50% of the daylight (not really much of a see-through display at this point) they don’t work in daylight.   There is a reason why companies are making purpose built HUDs.

The cd/m2 also is a big issue for outdoor head mount display use. Depending on the application, they may need 10,000 cd/m2 or more and this can become very challenging with some types of displays and keeping within the power and cooling budgets.

At the other extreme at night or dark indoors you might want the display to have less than 100 cd/m2 to avoid blinding the user to their surrounding.  Note the SMPTE spec for movie theaters is only about 50 cd/mso even at 100 cd/m2 you would be about 2X the brightness of a movie theater.  If the device much go from bright sunlight to night use, you could be talking over a 1,500 to 1 dynamic range which turns out to be a non-trivial challenge to do well with today’s LEDs or Lasers.

Eye-Box and Exit Pupil

Since AR HMDs and HUDs generate images for a user’s eye in a particular place, yet need to compete with the ambient light, the optical system is designed to concentrate light in the direction of the eye.  As a consequence, the image will only be visible in a given solid angle “eye-box” (with HUDs) or “pupil” (with near eye displays).   There is also a trade-off in making the eyebox or pupil bigger and the ease of use, as the bigger the eye-box or pupil, the easier it will be the use.

With HUD systems there can be a pretty simple trade-off in eye-box size and cd/m2 and the lumens that must be generated.   Using some optical tricks can help keep from needing an extremely bright and power hungry light source.   Conceptually a HUD is in some ways like a head mounted display but with very long eye relief. With such large eye relieve and the ability of the person to move their whole head, the eyebox for a HUD has significantly larger than the exit pupil of near eye optics.  Because the eyebox is so much larger a HUD is going to need much more light to work with.

For near eye optical design, getting a large exit pupil is a more complex issue as it comes with trade-offs in cost, brightness, optical complexity, size, weight, and eye-relief (how far the optics are from the viewer’s eye).

Too small a pupil and/or with more eye-relief, and a near eye device is difficult to use as any small movement of the device causes you to to not be able to see the whole image.  Most people’s first encounter with an exit pupil is with binoculars or a telescope and how the image cuts offs unless the optics are centered well on the user’s eye.

Conclusions

While I can see that people are excited about the possibilities of AR and VR technologies, I still have a hard time seeing how the numbers add up so to speak for having what I would consider to be a mass market product.  I see people being critical of Hololens’ lower FOV without being realistic about how they could go higher without drastically sacrificing angular resolution.

Clearly there can be product niches where the device could serve, but I think people have unrealistic expectations for how fast the field of view can grow for product like Hololens.   For “real work” I think the lower field of view and high angular resolution approach (as with Hololens) makes more sense for more applications.   Maybe game players in the VR space are more willing to accept 1970’s type angular resolution, but I wonder for how long.

I don’t see any technology that will be practical in high volume (or even very expensive at low volume) that is going to simultaneously solve the angular resolution and FOV that some people want. AR displays are often brightness challenged, particularly for outdoor use.  Layered on top of these issues are those size, weight, cost, and power consumption which we will have to save these issues for another day.

 

Wrist Projector Scams – Ritot, Cicret, the new eyeHand

ritot-cicret-eyehand-001Wrist Projectors are the crowdfund scams that keeps on giving with new ones cropping up every 6 months to a year. When I say scam, I mean that there is zero chance that they will ever deliver anything even remotely close what they are promising. They have obviously “Photoshopped”/Fake pictures to “show” projected images that are not even close to possible in the the real world and violate the laws of physics (are forever impossible). While I have pointed out in this blog where I believe that Microvision has lied and mislead investors and showed very fake images with the laser beam scanning technology, even they are not total scammers like Ritot, Cicret, and eyeHand.

According to Ritot’s Indiegogo campaign, they have taken in $1,401,510 from 8917 suckers (they call them “backers”).   Cicret according to their website has a haul of $625,000 from 10,618 gullible people.

Just when you think that Ritot and Cicret had found all the suckers for wrist projectors, now CrowdFunder reports that eyeHand has raised $585,000 from individuals and claims to have raised another $2,500,000 in equity from “investors” (if they are real then they are fools, if not, then it is just part of the scam). A million here, $500K there, pretty soon you are talking real money.

Apparently Dell’s marking is believing these scams (I would hope their technical people know better) and has show video Ads that showed a similar impossible projectors.  One thing I will give them is that they did a more convincing “simulation” (no projecting “black”) and they say in the Ads that these are “concepts” and not real products. See for example the following stills from their Dell’s videos (click to see larger image).  It looks to me like they combined a real projected image (with the projector off camera and perpendicular to the arm/hand) and then add fake projector rays to try and suggest it came from the dummy device on the arm): dell-ritots-three

Ritot was the first of these scams I was alerted to and I help contribute some technical content to the DropKicker article http://drop-kicker.com/2014/08/ritot-projection-watch/. I am the “Reader K” that they thanked in the author’s note at the beginning of the article.  A number of others have called out the Ritot and Cicret as being scams but that did not keep them from continuing to raise money nor has it stopped the new copycat eyeHand scam.

The some of key problems with the wrist projector:

  1. Very shallow angle of projection.  Projectors normally project on a surface that is perpendicular to the direction of projection, but the wrist projectors have to project onto a surface that is nearly parallel to the direction of projection.  Their concepts show a projector that is only a few (2 to 4) millimeters above the surface. When these scammers later show “prototypes” they radically change the projection distance and projection angle.
  2. Extremely short projection distance.  The near side of the projection is only a few millimeters away while the far side of the image could be 10X or 50X further away.  There is no optics or laser scanning technology on earth that can do this.  There is no way to get such a wide image at such a short distance from the projector.  As light falls off with the square of distance, this results in an impossible illumination problem (the far side being over 100X dimmer than the near side).
  3. Projecting in ambient light – All three of the scammers show concept images where the projected image is darker than the surrounding skin.  This is absolutely impossible and violates the laws of physics.   The “black” of the image is set by the ambient light and the skin, the projector can only add light, it is impossible to remove light with a projector.  This shows ignorance and/or a callous regard for the the truth by the scammers.
  4. The blocking of the image by hairs, veins, and muscles.  At such a shallow angle (per #1 above) everything is in the way.
  5. There is no projector small enough.  These projector engines with their electronics that exist are more than 20X bigger in volume than what would be required to fit.
  6. The size of the orifice through with the light emerges is too small to support the size of the image that they want to project
  7.  The battery required to make them daylight readable would be bigger than the whole projector that they show.  These scammers would have you believe that a projector could work off a trivially small battery.
  8. Cicret and eyeHand show “touch interfaces” that won’t work due to the shallow angle.  The shadows cast by fingers working the touch interface would block the light to the rest of the image and made “multi-touch” impossible.   This also goes back to the shallow angle issue #1 above.

The issues above hold true whether the projection technology uses DLP, LCOS, or Laser Beam Scanning.

Cicret and Ritot have both made “progress reports” showing stills and  videos using projectors more than 20 times bigger and much higher and farther away (to reduce the projection angle) than the sleek wrist watch models they show in their 3-D CAD models.   Even then they  keep off-camera much/most of the electronics and battery/power-supply necessary needed to drive the optics that the show.

The image below is from a Cicret “prototype” video Feb of 2015 where they simply strapped a Microvision ShowWX+ HMDI upside down to a person’s wrist (I wonder how many thousand dollars they used engineering this prototype). They goofed in the video and showed enough of the projector that I could identify (red oval) the underside of the Microvision projector (the video also shows the distinctive diagonal roll bar of a Microvision LBS projector).  I have show the rest of the projector roughly to scale in the image below that they cropped off when shooting the video.  What you can’t tell in this video is that the projector is also a couple of inches above the surface of the arm in order to project a reasonable image.

cicret-001b

So you might think Cicret was going to use laser beam scanning, but no, their October 2016 “prototype” is showing a panel (DLP or LCOS) projector.  Basically it looks like they are just clamping whatever projector they find to a person’s wrist, there is no technology they are developing.  In this latest case, it looks like what they have done is found a small production projector taken its guts out and put it in a 3-D printed case.  Note the top of the case is going to be approximately 2 inches above a person’s wrist and how far away the image is from the projector.

cicret-002e

Ritot also has made update to keep their suckers on the hook.   Apparently Indiegogo only rule is that you much keep lying to your “backers” (for more on the subject of how Indiegogo condones fraud click here).  These updates at best show how little these scammers understood projection technology.   I guess one could argue that they were too incompetent to know they were lying.  ritot-demo-2014

On the left is a “demo” Ritot shows in 2014 after raising over $1M.  It is simply an off the shelf development system projector and note there is no power supply.  Note they are showing it straight on/perpendicular to the wrist from several inches away.

ritot-2015By 2015 Rito had their own development system and some basic optics.  Notice how big the electronics board is relative to the optics and that even this does not show the power source.

By April 2016 they showed an optical engine (ONLY) strapped to a persons wrist.  ritot-2016-04-20-at-25sCut off in the picture is the all the video drive electronics (see the flex cable in the red oval) that is off camera and likely a driver board similar to the one in the 2015 update  and the power supplies/battery.

In the April 2016 you should notice how the person’s wrist is bent to make make it more perpendicular to the direction of the projected image.  Also not that the image is distorted and about the size of an Apple watch’s image.   I will also guarantee that you will not have a decent view-able image when used outdoors in daylight.

The eyeHand scam has not shown anything like a prototype, just a poorly faked (projecting black) image.  From the low angle they show in their fake image, the projected would be blocked by the base of the thumb even if the person hold their hand flat.  To make it work at all they would have to move the projector well up the person’s arm and then bend the wrist, but then the person could not view it very well unless they hold their arm at an uncomfortable angle.  Then you have the problem of keeping the person from moving/relaxing their wrist and loosing the projection surface.   And of course it would not be view-able outdoors in daylight.

It it not like others have been trying to point out that these projectors are scams.  Google search “Ritot scam” or “Cicret scam” and you will find a number of references.  As best I can find, this blog is the first to call out the eyeHand scam:

  • The most technically in depth article was by Drop-Kicker on the Ritot scam
  • Captain Delusional has a  comic take on the Cicret scam on YouTube – He has some good insights on the issue of touch control but also makes some technical mistakes such as his comments on laser beam scanning (you can’t remove the laser scanning roll-bar by syncing the camera — also laser scanning has the same fall-off in brightness due do the scanning process).
  • Geek Forever had an article on the Ritot Scam 
  • A video about the Ritot Scam on Youtube
  • KickScammed about Ritot from 2014

The problem with scam startups is that they tarnish all the other startups trying to find a way to get started.  Unfortunately, the best liars/swindlers often do the best with crowdfunding.  The more they are willing to lie/exaggerate, the better it makes their product sound.

Indiegogo has proven time and again to have extremely low standards (basically if the company keep posting lies, they are good to go – MANY people tried to tell Indiegogo about the Ritot Scam but to no avail before Ritot got the funds). Kickstarter has some standards but the bar is not that large but at least I have not see a wrist projector on Kickstarter yet. Since the crowdfunding sites get a cut of the action whether the project delivers or not, their financial incentives are on the side of the companies and the people funding. There is no bar for companies that go with direct websites, it is purely caveat emptor.

I suspect that since the wrist projector scam has worked at least three (3) times so far, we will see other using it.   At least with eyeHand you have a good idea of what it will look like in two years (hint – like Ritot and Cicret).