HDR -> SDR conversion

These CUDA filters are packaged into DGDecodeNV, which is part of DGDecNV.
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admin
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Re: HDR -> SDR tonemapping

Post by admin »

I'm recommending a small change to the Avisynth+ script that improves things a bit. Note the ConvertBits() call:

loadplugin("DGDecodeNV.dll")
loadplugin("DGTonemap.dll")
loadplugin("avsresize.dll")
SetFilterMTMode("z_ConvertFormat", MT_MULTI_INSTANCE) # May not be needed.
DGSource("THE GREAT WALL.dgi",fulldepth=true)
ConvertBits(10) # use 12 for 12-bit
z_ConvertFormat(pixel_type="RGBPS",colorspace_op="2020ncl:st2084:2020:l=>rgb:linear:2020:l", dither_type="none")
# Choose one of these:
DGReinhard()
#DGHable()
z_ConvertFormat(pixel_type="YV12",colorspace_op="rgb:linear:2020:l=>709:709:709:l",dither_type="ordered")
prefetch(4)
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Re: HDR -> SDR tonemapping

Post by Guest »

Do you require any testing or comparisons done with the change?
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Re: HDR -> SDR tonemapping

Post by admin »

No thank you, gonca, I've tested it and confirmed to my satisfaction that it works a little better. If you stumble across anything, though, please report it.

I got an email from someone thinking there is no difference between fulldepth=true and fulldepth=false. The difference between 8 and 10 bits is just 2 bits, i.e., a maximum difference of 4. So if you just look at the frames, you may not see a gross difference, especially if there are no large flat areas where you would see banding. However, if you do a subtract between the two and then do levels in VirtualDub(2) and preview/sample frame, you can see the spike of differences that is 4 pixels wide. If you zoom in the two ends of the Input levels slider to just bracket the spike, then you can see the detail that is being retained in those lower two bits. Those 2 bits break what would have been a difference of 1 to a difference of 4, or to say it another way, the granularity is improved by a factor of 4, and that's why banding is significantly reduced.
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Re: HDR -> SDR tonemapping

Post by Guest »

Okay.
I asked you before if fulldepth=True operated the same as fulldepth=false on 8 bits sources.
I believe you said yes, so I always include True.
10 bit sources get passed as 10 bit, 8 bit sources get passed as 8 bit
I realize that on some sources 8 or 10 bit makes little difference, but on some the extra 2 bits can make a lot of difference on detail and color retention.
One question though
The ConvertBits(10) call comes after DGSource(xxx, fulldepth=True)
Shouldn't the output of DGSource already be 10 bit?
I do realize that if the source is 8 bit running it in 10 bit can be beneficial, especially in terms of banding, but the source should already be 10 bit as this should be a hdr source.
I am not questioning you so much as I am asking for info/knowledge on the why
Either way thank you for your continuous efforts and improvements to your software :salute:
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Re: HDR -> SDR tonemapping

Post by admin »

DGSource(fulldepth=true) outputs 16-bit always, with the extra bits zeroed, i.e., for 10-bit source, the lower 6 bits are zero. So the ConvertBits() call gets rid of the extra lower bits. I did a subtract+levels test between the frames with and without the ConvertBits() and was able to see some extra detail being retained with the ConvertBits().

I welcome being questioned because I am a seeker after truth and things should stand up to scrutiny and healthy skepticism.

Off to the pool!
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Re: HDR -> SDR tonemapping

Post by Guest »

Quick 2 questions
On hdr to hdr cases would you recommend using ConvertBits(10) for 10 bit sources to 10 bit output

On sdr to sdr cases would you recommend using ConvertBits(8) or fulldepth=False (8bit source to 8 bit output) :?:
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Re: HDR -> SDR tonemapping

Post by admin »

gonca wrote:
Wed Apr 18, 2018 5:59 pm
On hdr to hdr cases would you recommend using ConvertBits(10) for 10 bit sources to 10 bit output?
It depends on what your encoder wants to receive. Otherwise, it doesn't matter, unless you doing some gamma adjustment or something unusual like that. In that case, umm, it depends. :lol:
On sdr to sdr cases would you recommend using ConvertBits(8) or fulldepth=False (8bit source to 8 bit output)?
Neither one is necessary as 8-bit will always be delivered as 8-bit. Anyway, fulldepth=false by default.
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Re: HDR -> SDR tonemapping

Post by Guest »

Do you know how to use ConvertBits() in VS? Is it doable?
Would fmtconv work as well as ConvertBits()?
I guess I can always convert my scrips to avs+ again
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DJATOM
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Re: HDR -> SDR tonemapping

Post by DJATOM »

fmtc can do bits conversion. If you don't want to convert with fmtc, internal resizers can perform bits conversion as well:

Code: Select all

from vapoursynth import core, YUV420P16
...
clip = core.resize.Point(clip, format=YUV420P16)
PC: RTX 2070 | Ryzen R9 5950X (no OC) | 64 GB RAM
Notebook: RTX 4060 | Ryzen R9 7945HX | 32 GB RAM
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Re: HDR -> SDR tonemapping

Post by Guest »

Thank you
ConvertBits apparently drops the padded (zeroed) bits
fmtc dithers down
Would this affect the quality?
How do the internal resizers function, dithering, dropping padded zeroes?
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Re: HDR -> SDR tonemapping

Post by admin »

Now, that is a great question, because if they are dithering down, then the "extra detail" I saw may be just dithering. I will check the Avisynth+ and Vapoursynth source code today.
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Re: HDR -> SDR tonemapping

Post by DJATOM »

ConvertBits(8) just drops the Least significant bit, so you need to add dither=0 or 1, whatever method you want to use there.
PC: RTX 2070 | Ryzen R9 5950X (no OC) | 64 GB RAM
Notebook: RTX 4060 | Ryzen R9 7945HX | 32 GB RAM
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Re: HDR -> SDR tonemapping

Post by Guest »

According to this link the default is to not add dither
http://avisynth.nl/index.php/ConvertBits

dither = -1
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Re: HDR -> SDR tonemapping

Post by admin »

You beat me to it, I was just looking over there. That's what we want, no dithering. Thanks, guys.
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Re: HDR -> SDR tonemapping

Post by admin »

DJATOM wrote:
Thu Apr 19, 2018 4:42 am

Code: Select all

clip = core.resize.Point(clip, format=YUV420P16)
That doesn't convert to 10-bit. I think this is correct:

import vapoursynth as vs
core = vs.get_core()
...
clip = core.resize.Point(clip, format=vs.YUV420P10)
...
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Re: HDR -> SDR tonemapping

Post by Guest »

Code: Select all

clip = core.resize.Point(clip, format=vs.YUV420P10)
will convert to 10 bit, but do I need to use

Code: Select all

clip = core.resize.Point(clip, format=vs.YUV420P10, dither_type=none)
to ensure that no dither is used?
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Re: HDR -> SDR tonemapping

Post by admin »

dither_type none is the default.
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Re: HDR -> SDR tonemapping

Post by Guest »

Thank you
I didn't see that mentioned in the docs I looked at,
at least not in a way that I understood
:hat:
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Re: HDR -> SDR tonemapping

Post by admin »

See HolyWu on June 28, 2017 at 12:55 in this thread:

http://www.vapoursynth.com/discussion/
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Re: HDR -> SDR tonemapping

Post by Guest »

Thanks
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Re: HDR -> SDR tonemapping

Post by admin »

You are welcome. It's always my pleasure.
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Re: HDR -> SDR tonemapping

Post by admin »

So, we have established that we need to do the 2020->709 conversion and the tonemapping all together on the GPU if we expect CUDA to give us good performance gains. So I have been researching how to do that. Here is my tentative plan for the 2020->709 part. If it pans out then tonemapping can be added. Please advise if I am planning anything stupid. I'm a bit of a dilettante in the colorimetry area, so...

Code: Select all

Convert HDR 10-bit in YUV420P16 to YV12

Step 1: Convert to P10.

Strip lower 6 bits (zeros)

Step 2: Convert to RGB

R = 1.164(Y-64) + 1.596(V-512)
G = 1.164(Y-64) - 0.813(V-512) - 0.392(U-512)
B = 1.164(Y-64) + 2.017(U-512)

Step 3: Linearize

R = R * R
G = G * G
B = B * B

Step 4: Map the gamut using inverse of rec 2087 matrix

R          1.6605  -0.5877  -0.0728     R
G      =  -0.1246   1.1330  -0.0084  *  G
B         -0.0182  -0.1006   1.1187     B
709                                     2020

Step 5: Gamma correct

R = sqrt(R)
G = sqrt(G)
B = sqrt(B)
clamp as needed

Step 6: Convert to 8-bit YUV

Y =  (0.257 * R) + (0.504 * G) + (0.098 * B) + 16
U = -(0.148 * R) - (0.291 * G) + (0.439 * B) + 128
V =  (0.439 * R) - (0.368 * G) - (0.071 * B) + 128

This can now be returned as YV12 for Avsynth+.
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Re: HDR -> SDR tonemapping

Post by Guest »

I am a complete rookie at the color thingy, but based on all the stuff I have read on the topic, before my eyes glazed over, your approach seems to be spot on from the format (2020 to 709) to the clamping of the levels to accommodate the 8 bit standard
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Re: HDR -> SDR tonemapping

Post by admin »

OK, good to hear. Of course, there are a lot of ways to map the out-of-gamut values back into range, but it seemed sensible to me to just reverse what is given for 709->2020 in REC 2087.

https://www.itu.int/dms_pubrec/itu-r/re ... !PDF-E.pdf
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Re: HDR -> SDR tonemapping

Post by Guest »

It does appear to be a logical approach
If
A>black box >B
then
B> inverse black box >A
Only in this case the black box is a known algorithm
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