Laser projectors general? [zero lag & zero blur!!!]

[spacediver]

HDR is probably the most important development in display technology since the transition to HD. It is far from a gimmick.

what is hdr and why do i care?
isn't it just making displays brighter? then i don't really care because indoors, anything >100nits is too bright for me

hehe, I'll take your bait and play along for the benefit of others

Some discussion here:

http://hardforum.com/showthread.php?t=1886244

Here's a great video to introduce the main ideas:

https://www.youtube.com/watch?v=nZWWbx6vGk8

Having a larger range of luminances to work with, along with a higher bit depth, allows some a greater amount of realism, in both the intensities of light, and in the amount of information that can be encoded. Joel Barsotti gives a good example in the video at 16:30


HDR isn't just a simple scaling up of luminance of the entire image. It requires newly mastered content. A lot of the high luminance stuff, for example, will be used for specular highlights.

[Light23]

Haha, that's funny, I was considering buying two of these pico projectors to do just that, run them in parallel to do pseudo HDR.

The problem I ran into is that there is no lens, hence no lens shift, so aligning the images will be impossible unless you're willing to offset the top and bottom projected image in software.

Which would work for letterbox movies actually, you run one MPC-HC window at 3840x1080 and write a shader that displays the low dynamic range on the left and the higher dynamic range on the right, with the appropriate tone mapping obviously (and some falloff / blending between the two so there isn't a sharp discontinuity) and of course the appropriate vertical "software lens shift" to each of the left/right subframes independently. Writing such a shader would be pretty fun and pretty easy (I wrote one to correct chromatic aberration from anamorphic lenses and shared it on ShaderToy a while back).

The other problem for this is the fact that the "high dynamic range" subframe would be still pretty dim, so that one you would have to seriously boost the lumens of at least one of your projectors (like, by a factor of ten or more). Of course if you keep the projected image size very low as you appear to be doing with your home made screen setup, I think you can definitely do it.

Also, don't forget, 8-bit range for the low end and 8-bit range of DR for the high end results in a 9-bit effective DR display. You would obviously concentrate the lower 8-bit to handle, say, from 0-100 nits in the HDR signal, and the higher end to handle 100-1000. You could also just clip some of the high end DR to reduce the banding further, for instance let's say your original HDR movie rip (in 10-bit, HDR10 format) indeed goes from 0-1000 nits in range. So let's say you clip the top 50%, so your range of valid values becomes 0-500 nits. Then suddenly, you can do something like 0-50 nits is the low dynamic range projector's duty, then 50-500 is the job of the high DR's projector duty. I believe HDR done this way (or something like it), using two 8-bit projectors resulting in 9 effective bits of DR total, could do 0-500 nits without banding artifacts.


Let me know if you need help writing the MPC-HC shader that does the image offsets to align the images together. Of course this is for movies only. If you want an HDR gaming TV you will need to write custom code, perhaps through raspberry PI which is dirt cheap and has HDMI inputs and outputs. You would still lose a few lines of addressable vertical resolution but it could be done without scaling the input (just an offset in UV coordinates at pixel resolution increments = no scaling)

RLBURNSIDE I REALLY like some of your ideas man!

(Right now I am achieving a perfect overlap with the two Sony projectors using a P.B.S. cube in an L configuration. )
I like your idea about the shaders for HDR. I will PM you later with some more details about the setup. Hopefully together we can come up with something clever to achieve HDR in this laser monitor.


-Möbius Loop Ron Paul NOT included within monitor housing.-(Political associations sold separately)

[RLBURNSIDE]

Thanks man. As a pre-step for the HDR shader, I posted this on AVS forum, which is a soft-ware only solution for lens shift so you don't even need any prisms (which can degrade quality if I'm not mistaken).

cross post from here: http://www.avsforum.com/forum/68-digita ... ing-4.html
---------------------------
Hi guys, I wrote a quick shader in ShaderToy that implements a software lens shift, for those of you who want to dual stack these projectors one on top of another, and run a separate HDMI output cable from your HTPC to each one, to double up the lumens.

https://www.shadertoy.com/view/ldV3zW

I'll make an MPC-HC version and paste it in there so that you can use it to playback videos.

All you need are two Sony / Celluon projectors, stack them one on top of the other, a windows PC with dual HDMI outputs on your videocard, then create a spanning desktop across both displays of 3840 x 1080 resolution, and adjust the software lens shift amount value in the shader until their projected images line up perfectly. The shader clips off some of the top of the "down" shifted left image, and some of the bottom of the right "upshifted" image, so you lose out on some of the original video, but that should happen anyway (or you would see some portion of each projected image without support from the other projector to boost the lumens).

If you play back letterbox movies you won't lose any actual video data or resolution in the original video, since you'll only be clipping off parts of black areas anyway.

[RLBURNSIDE]

Here's the proof of concept dual-projector HDR shader that builds on the lens shift one:

https://www.shadertoy.com/view/lsV3zW

Light123, if you actually get this working I'd appreciate if you shared the tuning values and/or equations you use. I could help iterate on it because I'm implementing HDR stuff at work and it's good practice.

Just try it in the window, I think with a spanning desktop you can make the web gl app fullscreen at 3840x1080 and test it without even having the media player classic version (which is HLSL I think. I converted my CA correction shader and it's easy to add it to the list of shaders you use in MPC-HC).

[RLBURNSIDE]

Well, the title of this thread is "laser projectors general", although rear projection could be considered similar to a traditional TV or monitor.

I agree about low refresh rates and scanned displays, I used to hate 60hz flicker on CRTs and wouldn't even consider using one lower than 72hz, 85+ ideally.

But running at 120hz would be great for a raster display, since it's a common multiple of 24, 30, and 60, and would result in pretty low lag and latency, plus it's easy to simply repeat frames to maintain the cadence of the original material.

Even if you enjoy frame interpolation (like I do) on movies, if you had, say, a 72hz or 120hz display instead of a 60hz one, and was watching lowly 24p movies interpolated, then the quality of the interpolation would be better for the simple fact that there's no cadence mismatch and you only see 2/3 or 4/5 of the frames are interpolated, with 1/3 or 1/5 being the original. That said, you'd still have to reduce the motion blur quite significantly in the "key" frames. Super fast frame rate with blurry frames looks the same, just a slightly smoother blur. That's actually the purpose of motion blur caked into the frames of 24p movies, it's to mask the low framerate. As soon as you run a higher framerate you need to first de-blur, then interpolate the sharper keyframes. And deblurring is a tough problem. It can be done but not perfectly.

I don't think this project makes sense at computer monitor sizes, personally. Especially not when OLED PC monitors are out now and prices will inevitably come down.

Do you use SVP for motion interpolation? What do you use for video deblurring? That's a great idea, i never thought about deblurring smudged frames to get the full benefit of motion interpolation.

Can you answer this please? it's very interesting.

Oh yeah, sorry. I definitely use and love SVP, the latest version (4) works really well and it's worth it to pay for it to get the Pro version (very cheap). I believe as part of their artifact removal efforts they do some kind of de-blurring first, but if you find any media player classic shaders that do a good job of motion de-blurring then you could feed that in to SVP afterwards, or you could run a pre-process script on all your videos. The cleaner the frames are the better the interpolation. Although there is a limit, some blur is actually good if you're using 60hz. 120hz or above I'd say completely remove all blur.

Check out this app, it's very handy way to compare various framerates and blur : https://frames-per-second.appspot.com/

What I've found is that even on 24 frames per second video, SVP works best when the bitrate of the rip is the highest. I watched Star Wars Ep 4 + 5 recently with SVP 4 and it was incredibly awesome, very clear and no artifacts almost throughout the entire movie. It felt "real", like I was there, and didn't detract from the originals in any way, just augmented the action because suddenly you can see the action without blur. On my 138 inch projected image I need all the framerate I can get, you notice everything on a projector. I even increase the upscaling filters quality to the max and that too makes a difference.

[RLBURNSIDE]

Updated the HDR shaders several times, I'm about at the limit of what I can try to achieve without actually having two projectors to toy with and some HDR 10 video (although I do have some downloaded somewhere)

[Light23]

Updated the HDR shaders several times, I'm about at the limit of what I can try to achieve without actually having two projectors to toy with and some HDR 10 video (although I do have some downloaded somewhere)

Fantastic work RLBURNSIDE!
If you can upload that HDR clip to the net & PM me a link to it so I can play around with this setup and we can figure out where to go next.

[flood]

Having a larger range of luminances to work with, along with a higher bit depth, allows some a greater amount of realism, in both the intensities of light, and in the amount of information that can be encoded. Joel Barsotti gives a good example in the video at 16:30


HDR isn't just a simple scaling up of luminance of the entire image. It requires newly mastered content. A lot of the high luminance stuff, for example, will be used for specular highlights.

yea so it's not too interesting from a technical perspective. in my mind it's sort of a buzzword like how "HD" was a few years ago

now if they can come up with something like low-latency tone-mapping so that hdr content can be displayed reasonably on displays with more limited luminance... that would be interesting.

[spacediver]

Having a larger range of luminances to work with, along with a higher bit depth, allows some a greater amount of realism, in both the intensities of light, and in the amount of information that can be encoded. Joel Barsotti gives a good example in the video at 16:30


HDR isn't just a simple scaling up of luminance of the entire image. It requires newly mastered content. A lot of the high luminance stuff, for example, will be used for specular highlights.

yea so it's not too interesting from a technical perspective. in my mind it's sort of a buzzword like how "HD" was a few years ago

now if they can come up with something like low-latency tone-mapping so that hdr content can be displayed reasonably on displays with more limited luminance... that would be interesting.

I believe that there are initiatives in place to do just this - algorithms that scale the mapping depending on the luminance range of the display. I remember reading or watching something about this recently.

[spacediver]

Light23, do you have any photos of your setup? Would be really cool to see some of the progress you've made.