Blur Busters Forums

flood wrote:

spacediver wrote: 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

RLBURNSIDE wrote: 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)

test123 wrote:

test123 wrote:

RLBURNSIDE wrote: 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.

RLBURNSIDE wrote: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)

spacediver wrote:
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.

flood wrote:

spacediver wrote:
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.