[info] [Wearables] So, what is wrong with HITL/microvision?

Wed Jan 9 13:20:28 UTC 2008

----- Forwarded message from Blair MacIntyre <blair at cc.gatech.edu> -----

From: Blair MacIntyre <blair at cc.gatech.edu>
Date: Wed, 9 Jan 2008 08:09:09 -0500
To: Ozan Cakmakci <ozan.cakmakci at gmail.com>
Cc: "wearables-list at media.mit.edu" <wearables-list at media.mit.edu>
Subject: Re: [Wearables] So, what *is* wrong with HITL/microvision?
X-Mailer: iPhone Mail (3B48b)

Cool stuff, ozan.  How big an fov can you hope to get?  I do AR, not  
HUD-based wearables, so 24 diagonal is not really useful;  40 is  
barely useful, much higher will be necessary in the long run.

---
Blair MacIntyre
Associate Professor, School of Interactive Computing, GVU Center
Georgia Tech, 85 5th Street NW, Atlanta, GA, 30308
(please excuse the terseness, this was sent from my phone)

On Jan 9, 2008, at 7:45 AM, Ozan Cakmakci <ozan.cakmakci at gmail.com>  
wrote:

>
> On Jan 8, 2008, at 9:52 PM, Blair MacIntyre wrote:
>
>> On Jan 8, 2008, at 8:28 PM, Adam Oranchak wrote:
>>
>>> Robin Lee Powell wrote:
>>>> I remember, and I'm sure some of you do to, Back In The Day when
>>>> HITL said they'd have full-resolution 24-bit colour in something  
>>>> the
>>>> size of a grain of rice or whatever for a few hundred dollars.   
>>>> IIRC
>>>> "the day" was 1995 or so.
>>> Well, you just stepped into a realm that I am intimately aware of.
>>> (Yes,
>>> you cheeky ones, I said "intimately!") It just so happens that all
>>> those
>>> specifications neglected to tell you that the image was crap, that  
>>> if
>>> the display moved out of alignment from the wearer's eye by a
>>> millimeter
>>> off you lost half the image, that the corners were dark and
>>> pin-cushioned and that the 8 bits of red depth of one pixel appeared
>>> over the 8 bits of green produced by a pixel 10 pixels away. Oh
>>> yeah, it
>>> cost $20K.
>>
>> Wow ... tell us how you really feel, Adam.  Don't hold back.  :)
>>
>> Of course, never having used the original one, and having owned and
>> used a more modern $3.5K version of VRD (the "nomad expert
>> technician", I would suggest that readers take what you say with a
>> grain of salt.  I found the Nomad to be very nice.  Yes, there are
>> issues when you move rapidly, but aside from that, I found the image
>> quite good, the exit pupil large, the field of view better than most
>> other displays in that price range.
>>
>> I won't bother listing my "credentials", though.  I don't do HMD
>> optics, I just use them.
>>
>> All that said, to actually answer the first question:  rumor has it
>> that they will have a small, full-color prototype delivered to the
>> military this year.  I'm anxious to see it, as I still believe that
>> the VRD is the most promising approach to usable, high-res, wide- 
>> field-
>> of-view HMDs out there.   All other approaches seem to require lots  
>> of
>> big crap in front of your face, which just won't cut the mustard with
>> the general public.
>>
>> cheers,
>>  blair
>
> There is another promising approach which is not studied extensively  
> - limits of a single mirror. We are trying to look in the direction  
> outlined below with Adam's help on industrial design and opto- 
> mechanical design.
>
> Starting to believe that an alternative ideal solution to not  
> requiring big crap in front of your face is to use a single free- 
> form off-axis mirror as a magnifier. Free-form to say that  
> rotationally symmetric aspheres are unlikely to perform in this  
> geometry. Off-axis to say that there is no single axis around which  
> the system is symmetric.
>
> I'm unsure how the optics would have a lower element count than a  
> single optical element + the microdisplay. Given the lack of space/ 
> volume to place the optics, lower element count designs seem to be  
> helpful. Additionally, such a configuration has no moving parts  
> which is desirable.  Single mirror has no dispersion so color  
> correction is not needed. We just fabricated a single free-form  
> mirror that is designed for 24 degrees full field diagonal with 20%  
> light at the Nyquist frequency of the modulation transfer function  
> (MTF). It is being assembled right now, we will know more soon. I  
> don't know too much about molding free-form parts but I've heard  
> people say that it can be mass manufactured for about a few dollars.  
> Yes, there will be issues with manufacturing tolerances but I  
> believe they will not require invention for their solutions. This  
> would potentially let people get into the <100 USD/hmd range.
>
> We have to optimize the mirror surface (coefficients describing the  
> mirror) across a particular field of view to get the best image  
> quality possible (<5% distortion + 20% light at Nyquist as  
> determined by the pixel spacing on the microdislay). The geometry of  
> a single mirror + microdisplay is highly constrained from an  
> optimization point of view. There are not that many degrees of  
> freedom to optimize to achieve the goal of good image quality. Tilt  
> of the mirror is set to an absolute minimum to reduce the angles of  
> incidence on the mirror. In such a configuration, the shape of the  
> mirror seems to turn into the major optimization variable. The  
> consequence is that how we describe shape becomes important. Free- 
> form usually means Zernike or x-y polynomials for the description of  
> shape. We are finding out that we might need to change the basis for  
> describing locally anamorphic pieces along the mirror surface. We  
> have been experimenting with optimizing the radial basis function  
> network representation (RBFN) with a Gaussian basis to represent the  
> mirror surface. Initial results indicate that you gain 20% MTF  
> compared to standard descriptions of free-form shapes such as  
> anamorphic aspheres, Zernike polynomials and x-y polynomials (we had  
> a submission pending with optics express which just got accepted  
> this morning :). The surface will remain manufacturable through  
> diamond turning as long as the rotationally non-symmetric sag from  
> the best fit sphere is kept within a few hundred micrometers. This  
> seems to be the case for the specific configuration of a single  
> element magnifier described using an RBFN description. Another  
> concern is alignment tolerances but we learned through fabricating  
> dual-element magnifiers that the alignment tolerances are not as bad  
> as people think they are. Anyway, what can we do with the gain in  
> performance (MTF) if we go to a different surface representation? It  
> may be traded off with a larger exit pupil size or a larger field of  
> view. Establishing the field of view and pupil size limits of a  
> single off-axis mirror seems relevant to this problem. In terms of  
> improving brightness, people are thinking about new microdisplays  
> that differ from LCD, OLED or a laser based source. It seems that  
> the brightness of microdisplays might increase considerably within  
> the next 5-10 years.
>
> Thank you,
> Ozan
>
>
>
>
>
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[info] [Wearables] So, what *is* wrong with HITL/microvision?

[info] [Wearables] So, what is wrong with HITL/microvision?