Hi, all,

This post might seem a bit random, but I've always been a big fan of 3D, and I've actually been working on some stuff for months now. The following is a bit complex, but I like to offload a lot of info in one hit, then see what you guys and gals think. So, sorry if it's a lot to read (let me know if it's too much) but it also gives a good background to how DLP projectors display images...

Firstly, I've built a blue-line decoder circuit, but it still doesn't sync properly as it has problems counting the Hsync pulse. It uses a PIC chip, and a "sync fixer" circuit to keep the Hsync / Vsync polarity positive. It then counts the sync pulses via an interrupt routine. The only way I've had this working so far is just to toggle the glasses on each alternate frame, then just swap the L / R images in Stereoscopic Player if they are wrong. The player keeps the L / R sync fine, so this seems to work, but is not ideal for cases when there are glitches and it looses sync.

I'm sure I'll get the blue-line stuff working at some point. The idea was that it would be completely programmable for different colour codes etc. It is also meant to be universal, so it has it's own voltage generators and should be able to power any shutter glasses directly (bypassing their original controller altogether!). It also has a DDC mode, so will work from an external L / R sync signal. Whatever you want really.

OK, so that's not quite working yet, but last night I had an "apostrophe"! (Only kidding, I meant an "Epithany"....

http://en.wikipedia.org/wiki/Epiphany_(feeling)

The thing is, my DLP projector (Acer PH-530) only seems to update at 60Hz even on the VGA input, so using shutter glasses is of course very flickery. This is also the one main drawback for most people who want 3D on a budget. So, I was thinking of ways to make the shutter glasses work at a higher frequency...
I even looked at how a control system would work for DLP projectors which update faster (say 120Hz), so I drew out some timing diagrams for how the frames would be stored in memory and the most effecient way of using the memory for 3D frames. I also looked at ways of joining two projectors together to make it output frames at twice the standard rate, although this is pretty pointless as you might as well go to a full PASSIVE setup anyway (if both projectors are working).

(some of the following has probably been discussed on here before, but it's worth mentioning again for people who didn't know)...

So the result of this is that I realized that main problem with the two-projector method (apart from cost) is that you can't take a standard DLP projector and close the shutter when the projector is half-way through a frame. The reason is that DLP projectors don't display a full FRAME of the image in one go and hold the image on the screen for the entire duration of the frame (eg. 16.6667ms for 60Hz, 5.5555ms per RGB colour).

In a DLP projector, the chip is actually monochromatic. It can ONLY show pixels which are completely ON or completely OFF at any one given time, afaik it CANNOT vary the brightness of each pixel directly. To create a full frame with the different variations in brightness, it takes the different "BIT weightings" of the frame, then displays them for different amounts of time for the duration of the frame. In DLP terminology, it calls these the "bitplanes". Of course, the projector also has to display the bitplanes for each colour (RGB), so there are quite a lot of bitplanes that the DLP chip displays just for a single colour frame.

This is the reason you can't shutter / blank a DLP projector mid-frame (it messes up the displaying of the bitplanes and would probably cause nasty image artifacts, or reduce the apparent brightness of the image by a large amount.)

What do I mean by "bitplanes" exactly? Well, if you know the basics of binary numbers, you probably have a good idea of how this works... For most digital displays nowadays, a single colour pixel is represented by 24-bits of information. This means that 8-bits (or one BYTE) is used to represent the "brightness" value of each of the colours (Red, Green, or Blue). With 8-bits, you can have a value from 0 to 255 for the brightness. 0 obviously means the darkest "black", and 255 means full brightness (ie. full white for B/W images, or full brightness for the specific RGB colour).

What most DLP projectors do is just store the full 24-bit pixel frame data into memory (as you normally would), then when it comes to display the frame (or one of the "colours") on the chip, it only takes ONE specific BIT for each pixel (as each pixel of the DLP chip can only be ON or OFF at one time). This BIT is taken from one our 8-bit information (for one colour, say RED).

(please keep in mind that a bitplane is a actually an entire FRAME of pixels on the whole surface of the DLP chip, not just a single pixel)

Since the DLP chip can't vary the brightness of each pixel directly, it must take advantage of the POV (Persistence Of Vision) of our eyes (just like old CRT TV's and many other display technologies). It does this by displaying each BIT of our 8-bit info for one pixel "colour", but gives different amounts of time to each BIT throughout the frame. So, in binary, the bits of one BYTE are often named 76543210. Where bit 7 is the MSB (Most Significant Bit)...

When respresnting a pixel brightness, it means that if bit 7 is ON (1), but all other bits are OFF (0), the pixel (or one of the RGB colours) would be at HALF brightness. So, when each bitplane is displayed on the DLP chip, it shows the bitplane representing bit 7 for the longest amount of time. Bit "6" of our byte represents HALF the brightness that bit 7 does, so it is displayed for only HALF of the duration...

So, to display all 8-bits of ONE colour (again, say RED for example), the projector shows the following "bitplanes" (I won't show bitplane 7 as it won't fit on a line!)...

6666666666666666666666666666666666666666666666666666666666666666 55555555555555555555555555555555 4444444444444444 33333333 2222 11 0

btw, the projector doesn't need to keep displaying the same bitplane over and over, it simply displays it once, then has a set delay before changing to the next bitplane. eg...

Display bitplane "7", hold for 8ms.
Display bitplane "6", hold for 4ms.
Display bitplane "5", hold for 2ms.
Display bitplane "4", hold for 1ms.
Display bitplane "3", hold for 0.5ms.
Display bitplane "2", hold for 0.25ms.
Display bitplane "1", hold for 0.125ms.
Display bitplane "0", hold for 0.0625ms.

This would make up 16ms of a 60Hz frame. (although, this example is for a B/W image - for RGB it would display three times faster of course).

Our eyes / brain are quite SLOW to respond to the changes of bitplanes (POV), so we merge them together and effectively see an image with ALL the brightness variations which make up one colour. It then obviously does the same for the GREEN and BLUE frames to make a full colour image (each colour change is synchronized to the colour wheel). A lot of projectors also have a "white" (clear) colour wheel segment, which is used to brighten up the peak whites of the image (I really hate this!).

Right, I think that's enough of that subject for a while (told you it was a long post!). I guess I could have just said the 3D idea from the start, but oh well.
I've split this into two posts, so this post was the background theory, the next post is my feeble idea...

OK, the idea was to have a new display method added to the software (Stereoscopic Player or whatever) which SWAPS bitplane 7 (the MSB) on alternate frames for the Left and Right frames. This MIGHT work for updating shutter glasses at a much faster rate (using ONE projector!). Remember, the only reason for all of this is finding a way of distributing the LEFT / RIGHT images between different bitplanes, so the glasses can run faster...

This is quite hard to explain, and I can see it is full of problems, but it would be something like this...

Frame 1...
7 6 5 4 3 2 1 0
L R R R R R R R

Frame 2...
7 6 5 4 3 2 1 0
R L L L L L L L

and so on.

So, bitplane 7 of the LEFT image is swapped with bitplane 7 of the RIGHT image. This should be quite easy to do in the playback software, but would require a controller for syncing the shutter glasses to the projector. The point is, is doesn't require modifying the projector itself in any way (although we might need to find which projectors are suitable).

The thing is, the above example might work if the projector was monochrome (or 3-chip), because bitplane 7 of the RIGHT image would be displayed directly after bitplanes 6 to 0 of the RIGHT image. But, all commercial single-chip DLP projectors have at least an RGB colour wheel, so the pattern would be more like this...

Frame 1 (RED)...
7 6 5 4 3 2 1 0
L R R R R R R R

Frame 1 (GREEN)...
7 6 5 4 3 2 1 0
R L L L L L L L

Frame 1 (BLUE)...
7 6 5 4 3 2 1 0
L R R R R R R R


Frame 2 (RED)...
7 6 5 4 3 2 1 0
R L L L L L L L

Frame 2 (GREEN)...
7 6 5 4 3 2 1 0
L R R R R R R R

Of course, we can't turn one colour into another as this is hard-wired by the design of the projector and colour wheel, so we can only swap bitplanes with the same colour in the NEXT frame.
ie. bitplane 7 (LEFT) of RED frame 1 matches with bitplanes 6-0 (LEFT) of RED frame 2. This causes a delay of entire colour frame between bitplane 7 and bitplanes 6-0.

The other problems are: each projector has a different number of colour wheel segments and different colour wheel speeds. Also, nearly all modern projectors have a more complex ordering for the bitplanes - The bitplanes are almost always displayed in a different order to the simpler example above, as this improves the image quality and reduces temporal effects.

The only good point is that bitplane 7 usually lasts for around HALF of each projected RGB "colour", so on a projector with a simple RGB colour wheel which only runs at 60Hz, using the above scheme would mean that there would be 6 shutter changes per frame - or in other words, the shutter glasses would need to work at 360Hz !!!

Anyway, I know it seems complex and problematic, but it's easy to understand once you realize how the bitplanes work and why they're necessary for DLP. This method will require different controller settings for different brands / models of projector. It might not even work, but I thought it would be interesting to explore.

Any thoughts on this? Is it useful at all for 3D?

Thanks for reading.

OzOnE.

Actually, scrap that last bit. When swapping the bitplanes on alternate frames, the shutter would not need to change when the next frame comes along.
So it's a bit difficult to work out the effective shutter speed. The above scheme would create around 3.5 shutter changes per frame (210Hz shutter for a 60Hz colour wheel projector).

The following should make the shutter update speed around 5.5 times the colour wheel speed (330Hz shutter for 60Hz projector)...

Frame 1 (RED)...
7 6 5 4 3 2 1 0
L R R R R R R R

Frame 1 (GREEN)...
7 6 5 4 3 2 1 0
L R R R R R R R

Frame 1 (BLUE)...
7 6 5 4 3 2 1 0
L R R R R R R R

Frame 2 (RED)...
7 6 5 4 3 2 1 0
R L L L L L L L

Frame 2 (GREEN)...
7 6 5 4 3 2 1 0
R L L L L L L L

The shutter updates kind of overlap, so it's not straightforward, but still a lot faster (if it will even work).

OzOnE.

WARNING: Do not read above message (too late) or you will end up with a headache like me now.

My Answer?
buy a DLP 3D ready projector.

I know, I have quite a headache myself. I often have that effect on people!

I agree that it's probably simpler to buy a 3D ready projector, but this method shouldn't actually be that difficult to implement as long as the image quality was any good. Besides, there are quite a few people on the forum who want a cheaper 3D solution and some very determined people who have got other weird and wacky ideas working.

The problem for me is that I can't afford to buy yet another projector and I was hoping this might help other people who are in the same boat. Also, most "3D ready" projectors can be seriously overpriced imho.

In most cases, it's still cheaper to buy two second-hand projectors and a silver screen AND two brand new lamps than to buy one of the new dual-input 3D projectors. Are there many older 120Hz capable projectors out there that can be found second-hand?

I realize that my new method isn't exactly universal, but that never stopped some of other solutions on the forum, and I've seen people go to quite some lengths to get stuff working. (I liked the photocell blue-line decoder btw)

Even better is when a solution forces the manufacturers to think again about their pricing plans.

I don't think it would be too difficult to add this display mode to some playback software. It just requires some basic testing of the controller after that to see if the image quality is good enough.

Anywho, just a thought.
OzOnE.

It's awesome that you're working on this as this is also my current obsession. I want to get my HD20 working in 3D and I can't yet justify buying a second one. I guess you're right that if I waited, I'd have to buy a new lamp for the older HD20 so both frames would be the same brightness, right? So I'll read over your whole thread when I have more time (got to go to work now) and work on this with you. You use a photocell placed infront of the projector to detect the sync??? That sounds nice and universal application! I'll read more thoroughly later. Have you read of other people's methods that worked for supposed "not 3d ready" 85hz dlp's like mine? Perhaps they were less universal but I'd be very interested just to get mine working. I've read all over about pass through dongles, and DIY pass through dongles and have that schematic from another site ... I was going to build one any day now ... Also, I read about using a second cheapy computer to run oscillator software and output a sync signal to shutterglasses via serial or was it parallel port (I might give this a try as it would be very adjustable - as long as it doesn't lose sync all the time). Sounds like you have read all this anyway.... Do they work?

TTYL, Awesome work,

TheDrummer

I also have a HD20 but am happy with anaglyph now I have my Pro ANA specs. FSX is superb, and far less hassle than the dated shutter glass system.

Actually, I think the photocell idea was Ragedemon's. I haven't tried this myself as I wanted to build a universal controller instead.

I've seen that some projectors (like certain InFocus based models) do speed up the colour wheel speed to match the vsync rate (within a certain range anyway). I think my X1 did this, but I've had an Acer for nearly three years now (is actually an Optoma clone), and it seems to only refresh at 60Hz?

Making a circuit to toggle shutter glasses on alternate VGA frames is fairly easy. The difficult part is counting the hsync pulses (lines), then detecting the blue-line code. My current circuit works fine in simulation, but not in real life as yet. It's a shame, because I wrote some fairly nifty features for it like shutter protection (when hsync or vsync is lost, or if vsync is below a set frequency). I'll get it working soon hopefully.

I wouldn't buy a second PC for running the glasses, this definitely sounds like a "sledgehammer to crack a nut" approach! It's easy enough to program a PIC chip to do this. You then just need a PCB which has two 15-pin VGA sockets on and extracting the appropriate signals.

Yes, a big problem is loosing sync because even if you use the vsync signal directly, one small glitch in the software might swap the L / R images. I had a lot of glitches with Revelator glasses on the nVidia drivers in the past, but I'm mainly interested in 3D movies now. Luckily, playing movies doesn't seem to glitch at all, even when decoding two 720p streams (this Quad Core and 3650 helps a lot though!).

@slipstream - tbh, I hadn't really tried anaglyph that often until recently, and although I've always wanted a proper full-colour setup, I have to admit that anaglyph can be pretty effective. You can get pretty good colour with the right settings, but you can't beat a full left / right setup for realism. What I'd really like is to watch 3D movies with family and friends on the big screen, so it ideally has to be the best it can be.

OzOnE.
btw, why does the text box keep scrolling while I'm trying to type a post and the text reaches the bottom of the text box!!!??? REALLY annoying. Is there a word limit on here or something?

uh, if you use DLP, you shouldnt use page flip mode, but checkerboard mode, and the dlp chip must understand that its 3d data, that way, instead of wobulating for better persistence or better whites, it will wobulate to generate separate left/right frames.

I wasn't really talking about wobulation as such - this is something which only really happens on certain new models of RPTV's. They "wobulate" the DMD to double the effective resolution on the screen. In other words, they might use a DMD chip with a resolution of only 720x360, they display half the pixels from the image, the whole chip is then physically moved (usually diagonally) by half a pixel width, then the second half of the pixels is displayed. This creates an effective resolution of 1280x720 on the screen.

Standard single-chip DLP projectors don't use wobulation at all afaik (at least I've never seen one which does?). For the "3D Ready" RPTV's which use wobulation, the 3D capability is more of a side-benefit of wobulation than a specific design feature. You often end up with half the resolution per eye with this technique though.

The idea of using a modified page-flipping scheme is to improve the shutter speed on existing "non 3D capable" projectors. Other than the often slow refresh (around 60Hz) with most projectors, shutter glasses are still one of the cheapest methods to achieve full-colour and good depth quality for 3D. So, it's only really the slow shutter speed which lets it down imo (which is generally a fault of the projector rather than the glasses).

I personally don't get on with anaglyph as it has a lot of problems with maintaining full colour at the same time as decent depth. It also hurts my eyes after a short while as I'm very sensitive to things like retinal rivalry and the way you get multiple colours on brighter parts of the image etc.

OzOnE.

Of course I understand the inherent problem with anaglyph and colour but I have never seen any difference with depth to be honest. Like I say I only use 3D for FSX and so have little or no red or cyan in the scenery so it looks great as far as I'm concerned. Real depth, it, for me, is just like flying with a pair of sunglasses on. I also understandthat you go slightly cross eyed too but I never suffer with headaches or anything to stop me using anaglyph.

I use page flip for my Infocus X1 and the 3D is absolutely superb. No ghosting or "wobulation" at all.

I agree that the 3D can look great with anaglyph and that sometimes the muted colours suit the content. Unfortunately, although I use my anaglyph glasses to quickly check 3D stills and for short clips, personally, I can't wear them for long sessions as I get severe eyestrain and sometimes even bloodshot eyes.

Gae43

I take some of that back - apparently many of the first 1080p projectors actually used wobulation. Whether they support 3D natively is a different matter though.

@Gae43 - Are you using 85Hz refresh with the X1? I remember that the colour wheel does speed up on the X1.

I found with anaglyph that even with "Black and white" + ana (B/W image, with ana "outlines"), or "True" ana (yellow where ana colours meet), I still get a lot of depth rivalry because the separation is never good enough and it still gets that off-putting colour mix in brighter areas. I don't think it could ever be called "true S3D", just my opinion.

I've always wanted a decent full-colour setup. If you've ever seen "Mickey's Philharmagic" 3D at Disney, you'll know what I mean.

OzOnE.

EDIT: btw, is there anyone else who is interested in developing my new display method further? I'm not the best programmer in the World, so I'll just e-mail Peter Wimmer now to see if he could possibly build a test version of Stereoscopic Player with this mode.

The idea is interesting, and it *could* work. But I'm not an expert for DLP technology...

I identified the following problems:

• Internal signal processing like brightness, contrast, gamma corrections done on the input data breaks the system because it will mix the MSB bit with the other bits.
• It requires DVI/HDMI/DirsplayPort. VGA doesn't work because it does not preserve the bit planes.

Doing bit plane modifications in a software player is fairly simple. If this idea works, I'll support it in the Stereoscopic Player. To support the development of this project, I've attached the source code of a DirectX application that shows how to implement software pageflipping. It might be helpful to create a test application for this project, although it still has to be modified to do the bit plane stuff.

Wow, thanks Peter!

That is an amazingly fast response. Thanks so much for the test program - it's not something I could have programmed myself from scratch.

I didn't even realize until last night that your player also supports effect control. This is another great project to play around with later (should be easy to make a serial port controller for relays etc.)

I realize there are a lot of pitfalls with the bitplane approach and that it would at least require a digital link to have a chance of working. I also see that almost all DLP projectors use bit-splitting, so the MSB is distributed throughout each colour frame too. This would mean the controller would need a sort of "map" for each type of projector / colour wheel. I see what you mean about VGA / analog connections too - only one bit of DAC / ADC error or noise and it could cause some nasty image effects.

I was hoping there might be a "middle-ground" with the brightness / contrast settings which might not affect the MSB too much if the controls are set to the right position?

The good news is that I have another project which connects directly to the projector to drive high-power RGB LEDs and completely replaces the colour wheel! Of course, brightness is the only problem but it's still very watchable when the room is dark. This project uses 15W LED's from LedEngin and the green LED alone produces around 600 to 700 lumens! The only other LED which emits as much light as this in a small area is of course the Phlatlight, but they are quite expensive.

Anyway, I digress. The LED project uses an FPGA instead of a PIC chip, but it simulates the colour wheel motor and directly generates the opto pulses etc. I could use something similar for this 3D display method which could simply work from the VGA sync (a PIC chip version appears to take more effort to get working properly). I need to buy another FPGA board though as I only have one, and don't want to take the LED projector apart yet.

Thanks again for this Peter - I'l start working on some basic controller code in the next few days and see if the image quality can be made decent enough. If the brightness and contrast controls can be left in the proper place, the other main problem is the full-frame of delay between the MSB and other bits.

I'll see how it goes.
Regards,
OzOnE (Ash).