[FFmpeg-user] Requesting colormatrix advice

markfilipak.imdb at gmail.com markfilipak.imdb at gmail.com
Tue Nov 7 12:21:03 EET 2023

On 11/7/23 04:08, Phil Rhodes via ffmpeg-user wrote:
>   I have no idea how colour handling in x265 works so I can't really advise on specifically how to set it up. Possibly it's documented somewhere. One of the problems with this (which comes up in some high end post production software quite often) is that it's sometimes not very clear whether we're specifying what we expect the input data to be, or what we expect it to be converted to.

I thought only I had that problem. :-)

> For instance, I'm not sure what's meant by "transfer" in this context.

Perfect example.

>> It's 1920x1080. I 'heard' of "studio swing". What is it relative to what x265 expects (above)? Do you know?
> I'm possibly guilty of indulging in jargon here; by "studio swing" I'm referring to a reduced data range often from 16-235 for the luminance channel.

The preferred term appears to be 'limited range'.

>>   I feel a headache coming on. Let's assume ffprobe is correct and colormatrix is undefined on the discs
> What's on the disc will be in Rec. 709.

I don't think so. If that were true, then what's on disc and what's in the MP4 would both play 
accurately and without saturation. I'm pretty sure they're not BT709.

> I honestly don't know what data ranges blu-rays use.

Limited. It's silly -- more legacy analog TV hangover -- but it's limited. The MPEG folks just can't 
seem to wean themselves away from TV-on-disc.

> It's often fairly clear if you can look at it and it looks all lifted, that'll be why.


> Unfortunately there are a lot of moving parts here.

I may be naive but I don't think so. X265 has presets that appear to cover all commercial media. How 
it covers is apparently a matter of some conjecture. But really, all that color adaptation stuff, 
like to accommodate phosphors in CRTs, needs to be done BY THE TV, not by the media. There should be 
one set of colors and they should be RGB full range with unlimited gamut. The TV makers know what 
the TVs are capable of and can do dot-by-dot fix up.

You're off the hook, Phil. Thanks for your thoughts. I appreciate them. -- Mark.

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