10-bit safe colors

leoenc · 8th January 2015, 13:03

I've posted this in the AutoAdjust forum with no replies so it might be more of a general AVIsynth topic:

Is it possible to use AVIsynth to limit the chroma and black levels of 10-bit video?
According to bt.709 specs we need to keep the Y within 64-940 and UV at 64-960, and black has to be limited at 64.

feisty2 · 8th January 2015, 13:24

here's the math
(1023-a)/(a-0)=(940-x)/(x-64)
#simplified version: (1023-0)/(a-0)=(940-64)/(x-64)
a is the value in full range (0-1023)
x is the target limited range value (64-940)
now all you have to do is convert the expression above to "x = ???? a" form and wrap it in Dither_lut16 ()
I don't wanna do it, cuz I might be the laziest guy on this planet :P
EDIT:
fine, here
Dither_lut16 ("x 876 * 1023 / 64 +", y=3, u=2, v=2)
Dither_lut16 ("x 896 * 1023 / 64 +", y=2, u=3, v=3)

colours · 8th January 2015, 17:27

What feisty2 posted is correct if your source is full-range 10-bit and is zero-padded in the MSB instead of LSB.

If all you want is to clip the Y/Cb/Cr values for a source that is already nominally limited-range 10-bit (with peaks/troughs that might exceed the 16/235/240 limits because of compression artifacts or whatever), that's easily done with Dither_lut16 too.

Code:

Dither_lut16(expr="x 4 / 16 max 240 min 4 *", yexpr="x 4 / 16 max 235 min 4 *", u=3, v=3) # zero padding in LSB
# OR (don't use both)
Dither_lut16(expr="x 256 / 16 max 240 min 256 *", yexpr="x 256 / 16 max 235 min 256 *", u=3, v=3) # zero padding in MSB

But of course we don't know that for sure, since you've not provided any information about your source. We're not psychic!

leoenc · 8th January 2015, 20:01

Thanks.
How can I tell if my source is full-range 10-bit and is zero padded in the MSB instead of LSB?
All I know about it is that its a ProRes high profile.
So far I was using FFvideoSource with the 10-bit hack to decode it, followed by f3kdb_dither, but I'm not sure I'm doing it right.

colours · 9th January 2015, 08:22

The builds of FFMS that have the enable10bithack option return the result with zero padding in the least significant bits. Not every source filter does the same thing, which is why confirming this is pretty important.

If you want to confirm whether your source is limited-range or full-range, put a Histogram() after the f3kdb_dither and look out for particularly dark or bright scenes. If you see white spots extending well into the brown regions, that means your source is full-range. If you don't, it could be either full-range or limited-range, and you should check other dark/bright scenes. (This is not an exact science and necessarily involves some guesswork.)

If it turns out that the source is limited-range (which I'm guessing it is, because full-range >8-bit is kind of rare), you can use either the Dither_lut16 line I posted before or the keep_tv_range option in f3kdb_dither.

hanfrunz · 9th January 2015, 10:43

To get legal and valid colors it's not enough to bring Y'CbCr values into the needed boundaries. You also have to limit in R'G'B' color space.

Some very interesting documents about this topic:
http://www.tek.com/document/applicat...illegal-colors
http://www.poynton.com/notes/video/Confusion.html

regards
hanfrunz

8th January 2015, 13:03	#1 \| Link
leoenc Registered User Join Date: Mar 2007 Posts: 192	10-bit safe colors I've posted this in the AutoAdjust forum with no replies so it might be more of a general AVIsynth topic: Is it possible to use AVIsynth to limit the chroma and black levels of 10-bit video? According to bt.709 specs we need to keep the Y within 64-940 and UV at 64-960, and black has to be limited at 64.

8th January 2015, 13:24	#2 \| Link
feisty2 I'm Siri Join Date: Oct 2012 Location: void Posts: 2,633	here's the math (1023-a)/(a-0)=(940-x)/(x-64) #simplified version: (1023-0)/(a-0)=(940-64)/(x-64) a is the value in full range (0-1023) x is the target limited range value (64-940) now all you have to do is convert the expression above to "x = ???? a" form and wrap it in Dither_lut16 () I don't wanna do it, cuz I might be the laziest guy on this planet :P EDIT: fine, here Dither_lut16 ("x 876 * 1023 / 64 +", y=3, u=2, v=2) Dither_lut16 ("x 896 * 1023 / 64 +", y=2, u=3, v=3) Last edited by feisty2; 8th January 2015 at 13:37.

8th January 2015, 17:27	#3 \| Link
colours Registered User Join Date: Mar 2014 Posts: 308	What feisty2 posted is correct if your source is full-range 10-bit and is zero-padded in the MSB instead of LSB. If all you want is to clip the Y/Cb/Cr values for a source that is already nominally limited-range 10-bit (with peaks/troughs that might exceed the 16/235/240 limits because of compression artifacts or whatever), that's easily done with Dither_lut16 too. Code: Dither_lut16(expr="x 4 / 16 max 240 min 4 ", yexpr="x 4 / 16 max 235 min 4 ", u=3, v=3) # zero padding in LSB # OR (don't use both) Dither_lut16(expr="x 256 / 16 max 240 min 256 ", yexpr="x 256 / 16 max 235 min 256 ", u=3, v=3) # zero padding in MSB But of course we don't know that for sure, since you've not provided any information about your source. We're not psychic! __________________ Say no to AviSynth 2.5.8 and DirectShowSource!

9th January 2015, 08:22	#5 \| Link
colours Registered User Join Date: Mar 2014 Posts: 308	The builds of FFMS that have the enable10bithack option return the result with zero padding in the least significant bits. Not every source filter does the same thing, which is why confirming this is pretty important. If you want to confirm whether your source is limited-range or full-range, put a Histogram() after the f3kdb_dither and look out for particularly dark or bright scenes. If you see white spots extending well into the brown regions, that means your source is full-range. If you don't, it could be either full-range or limited-range, and you should check other dark/bright scenes. (This is not an exact science and necessarily involves some guesswork.) If it turns out that the source is limited-range (which I'm guessing it is, because full-range >8-bit is kind of rare), you can use either the Dither_lut16 line I posted before or the keep_tv_range option in f3kdb_dither. __________________ Say no to AviSynth 2.5.8 and DirectShowSource!

8th January 2015, 20:01	#4 \| Link
leoenc Registered User Join Date: Mar 2007 Posts: 192	Thanks. How can I tell if my source is full-range 10-bit and is zero padded in the MSB instead of LSB? All I know about it is that its a ProRes high profile. So far I was using FFvideoSource with the 10-bit hack to decode it, followed by f3kdb_dither, but I'm not sure I'm doing it right.

9th January 2015, 10:43	#6 \| Link
hanfrunz Registered User Join Date: Feb 2002 Location: Germany Posts: 540	To get legal and valid colors it's not enough to bring Y'CbCr values into the needed boundaries. You also have to limit in R'G'B' color space. Some very interesting documents about this topic: http://www.tek.com/document/applicat...illegal-colors http://www.poynton.com/notes/video/Confusion.html regards hanfrunz