ColorMatrix HD -> SD conversion - am I using it correctly?

[orion44]

I have a 1080p video with a BT.709 colorimetry. I would like to convert it to SD resolution.

Is the following ColorMatrix conversion correct?

ColorMatrix(mode="Rec.709->Rec.601")

[kolak]

Yes, this is correct.

[ChaosKing]

But why should a lower res use a different colorimetry?

[FranceBB]

But why should a lower res use a different colorimetry?

Because SD contents are generally made with BT601. Sure, you can keep the BT709 and just flag the correct color matrix in your desired encoder (like x264), however since it's just a flag, there's no guarantee that the decoder will honour it as many deduct it from the resolution. This is pretty much the reason why it's always better to convert to BT601 when downscaling to SD.

Cheers,
Frank.

[lansing]

But why should a lower res use a different colorimetry?

I think this whole thing is just to prevent the media players from displaying the wrong color because by default, they are set to play videos that are less than 720p in bt601 and anything greater than that in bt709.

[ChaosKing]

So this would be a "crappy player fix" then :D

[manolito]

A short while ago I had a conversation about ColorMatrix and its alternatives in the AVS+ thread. Maybe read this link and my answer a few posts later...
https://forum.doom9.org/showthread.php?p=1868568#post1868568

If you refer to "crappy players" this probably includes a lot of hardware players which are only a couple of years old. The only way to find out if your player honors the colorimetry meta data is to make some tests. But if you want to play it safe then use BT709 for HD and BT601 for SD.


Cheers
manolito