чт, 4 авг. 2022 г., 09:28 Andrea paz <[email protected]>:
Thank you for the explanations. I am trying to write a color section for the CGG manual. I have a doubt: a long time ago GG said that on the timeline/compositor we always see an sRGB output:
"CinGG, works internally at 32 bits in RGB, but the output in timeline is sRGB, and performs a first conversion from YUV of the original file to RGB with the scaler (matrix function, not primaries or transfer characteristic function), using its internal settings."
Does this mean that it is useless to have wide-gamut monitors? And that it is useless to have ICCs or LUTs unless they are limited to sRGB only?
I think some ffmpeg plugins work internally in rgba-float, so correction happens with high precision, just display truncate/dither image. So yes, not truely 'what you see is what you get' {as far as I understand all image processing happens in linear space ? Because converting back and forth at each effect sounds wasteful on cpu ...} I wonder if mpv can read those yuv4mpeg raw streams with color transfer info? May be you can render to pipe and add mpv as gl accelerated and color-corrected external player? But I think fixing display stage will be as 'simple' as using specialised color-corrected rgba-float-> 10bit rgb (or may be dithered/tonemapped 8bit rgb) function, as long as display driver support 30 bit color. I commented in few bugs in the past: https://www.cinelerra-gg.org/bugtracker/view.php?id=297 https://www.cinelerra-gg.org/bugtracker/view.php?id=294 https://www.cinelerra-gg.org/bugtracker/view.php?id=238 If so, it would be extremely limiting for color correction
in CGG. My other doubt: what is the purpose of the "YUV color space" in Preferences, just for encoding?
I think it also used indirectly via FFVideoConvert::convert_vframe_picture in convert_cmodel function, in turn used by FFVideoStream::load all those in cinelerra/ffmpeg.C Any use of YUV type color spaces
should be discouraged since the signal on the screen is always sRGB.
Well, there is Xv (yuv) output, and encoded video tend to be variation of subsampled yuv (because it takes less space this way)
@Phyllis I have added a section in the manual on Color Management. See if it's okay. @All I also attach the txt file for those who would like to correct and improve it.
вс, 7 авг. 2022 г., 12:32 Andrea paz <[email protected]>:
@Phyllis I have added a section in the manual on Color Management. See if it's okay. @All I also attach the txt file for those who would like to correct and improve it.
Thanks! Is there possibility to extend section on XYZ colorspace, explaining it comes from experiments on how human eye receptors receive color (they obviously do not use technological rgb notation), because it was such source of confusion to me? Also, saying primaries are most possible colored points (greenest green in G direction, reddest red in R direction, etc) in choosen colorspace might be useful , at least I found those remarks clarifying illustrations nicely. Example of colormatrix settings also might be useful.
Is there possibility to extend section on XYZ colorspace, explaining it comes from experiments on how human eye receptors receive color (they obviously do not use technological rgb notation), because it was such source of confusion to me? Also, saying primaries are most possible colored points (greenest green in G direction, reddest red in R direction, etc) in choosen colorspace might be useful , at least I found those remarks clarifying illustrations nicely. Example of colormatrix settings also might be useful. Revision 2, after Andrew's suggestions. Talking about human vision and colormatrix settings are beyond my skill set and also too much for an introduction. I have put up a link that may be of interest. https://peteroupc.github.io/colorgen.html
вс, 7 авг. 2022 г., 22:01 Andrea paz <[email protected]>:
Is there possibility to extend section on XYZ colorspace, explaining it comes from experiments on how human eye receptors receive color (they obviously do not use technological rgb notation), because it was such source of confusion to me? Also, saying primaries are most possible colored points (greenest green in G direction, reddest red in R direction, etc) in choosen colorspace might be useful , at least I found those remarks clarifying illustrations nicely. Example of colormatrix settings also might be useful. Revision 2, after Andrew's suggestions. Talking about human vision and colormatrix settings are beyond my skill set and also too much for an introduction. I have put up a link that may be of interest. https://peteroupc.github.io/colorgen.html
Thanks! man ffmpeg-filters (for ffmpeg 5.0) Says about colormatrix example For example to convert from BT.601 to SMPTE-240M, use the command: colormatrix=bt601:smpte240m
Thank you Andrea for providing this information and putting it all together from various sources and your knowledge. I have proofread it, made minor changes like adding a comma or fixed misspelled word, and checked it into GIT. Note to others, Andrea does a lot of work to get this very nicely formatted and it is a lot of technical information and a great asset to the manual. Note to Andrea, since I do not really comprehend much of this, I do have a couple of questions: 1) What is "NB"? as in the line "ACES and OpenColorIO have an SRC workflow. *NB*: the monitor must still be calibrated to avoid unwanted color shifts." I noticed it is used in 6.1 the Proxy section also. I do not know what it represents. 2) Does "3..4" and "0..255" represent "from 3 to 4" and "0 to 255"? These are in your new CMS section. On Sun, Aug 7, 2022 at 1:09 PM Andrea paz via Cin < [email protected]> wrote:
Is there possibility to extend section on XYZ colorspace, explaining it comes from experiments on how human eye receptors receive color (they obviously do not use technological rgb notation), because it was such source of confusion to me? Also, saying primaries are most possible colored points (greenest green in G direction, reddest red in R direction, etc) in choosen colorspace might be useful , at least I found those remarks clarifying illustrations nicely. Example of colormatrix settings also might be useful. Revision 2, after Andrew's suggestions. Talking about human vision and colormatrix settings are beyond my skill set and also too much for an introduction. I have put up a link that may be of interest. https://peteroupc.github.io/colorgen.html -- Cin mailing list [email protected] https://lists.cinelerra-gg.org/mailman/listinfo/cin
Hi Phyllis, Andrea will surely answer you that it is Italian. "NB" in the context of this text is short for "Nota bene" which means "note well". https://en.wikipedia.org/wiki/Nota_bene I don't know Italian, but "NB" is sometimes used in French texts and is understood in the same way. Pierre Le 22-08-07 à 20 h 49, Phyllis Smith via Cin a écrit :
Note to Andrea, since I do not really comprehend much of this, I do have a couple of questions: 1) What is "NB"? as in the line "ACES and OpenColorIO have an SRC workflow. *NB*: the monitor must still be calibrated to avoid unwanted color shifts." I noticed it is used in 6.1 the Proxy section also. I do not know what it represents.
Oops Latin not Italian.... Pierre Le 22-08-07 à 21 h 15, Pierre autourduglobe a écrit :
Hi Phyllis, Andrea will surely answer you that it is Italian. "NB" in the context of this text is short for "Nota bene" which means "note well". https://en.wikipedia.org/wiki/Nota_bene
I don't know Italian, but "NB" is sometimes used in French texts and is understood in the same way.
Pierre
Le 22-08-07 à 20 h 49, Phyllis Smith via Cin a écrit :
Note to Andrea, since I do not really comprehend much of this, I do have a couple of questions: 1) What is "NB"? as in the line "ACES and OpenColorIO have an SRC workflow. *NB*: the monitor must still be calibrated to avoid unwanted color shifts." I noticed it is used in 6.1 the Proxy section also. I do not know what it represents.
Oh, thanks Pierre! I had no clue! On Sun, Aug 7, 2022 at 7:24 PM Pierre autourduglobe via Cin < [email protected]> wrote:
Hi Phyllis, Andrea will surely answer you that it is Italian. "NB" in the context of this text is short for "Nota bene" which means "note well". https://en.wikipedia.org/wiki/Nota_bene
I don't know Italian, but "NB" is sometimes used in French texts and is understood in the same way.
Pierre
Le 22-08-07 à 20 h 49, Phyllis Smith via Cin a écrit :
Note to Andrea, since I do not really comprehend much of this, I do have a couple of questions: 1) What is "NB"? as in the line "ACES and OpenColorIO have an SRC workflow. *NB*: the monitor must still be calibrated to avoid unwanted color shifts." I noticed it is used in 6.1 the Proxy section also. I do not know what it represents. -- Cin mailing list [email protected] https://lists.cinelerra-gg.org/mailman/listinfo/cin
Yes, Pierre is right. "NB" can be also translated as "note:". I'm sorry. 3..4 refers to the 3 color values + one alpha value, so it is better to put "3 or 4"; 0..255 is really a range and so "0 to 255" is fine.
participants (5)
-
Andrea paz -
Andrew Randrianasulu -
Igor BEGHETTO -
Phyllis Smith -
Pierre autourduglobe