A little confused on Colormatrix usage

[Adub]

Okay guys, I know this is a simple answer, but I can't seem to find a set, definitive answer anywhere.

Now, in order to preserve correct colors in a proper encode, a user should use Colormatrix.

Example: Encoding from MPEG2 to AVC.

Now, I think that MPEG2 uses rec.709, but AVC likes to use rec.601, correct? Thus, Colormatrix should be used to convert to the correct coefficents.

Am I wrong in my understanding?

In short, ASP and AVC should be encoded with rec.601 coefficients while Mpeg2 should stick with rec.709?

[45tripp]

I say it's all 601
(SD that is)

http://forum.doom9.org/showthread.php?t=131169

make up your own mind


gl

[Adub]

Really? So, you should just use the one that looks best?

I was hoping for a more factual response, sort of like I stated above.

[foxyshadis]

MPEG2 default is BT.709, MPEG4 default is BT.601 in SD, MPEG4 default in HD is BT.709. All of this can be overriden or ignored and often is. MPEG1 is always BT.601, that can't be overriden (but can be ignored, of course).

And in the end all video processing (and photography, and art, and...) is about what looks best - unfortunately the mind is also very easy to fool. The difference isn't enough for most people to pick up on without seeing both side by side, and even when they are, people can be hard pressed to decide which is "correct"; films are often given color casts by the lighting or film anyway.

Set the stream color to the same as the input, and ensure that you use a decoder that applies that, if you'd rather leave the headaches about 601/709 decoding behind.

[Adub]

Great post!
Thanks foxyshadis! That answered my question exactly. Okay, now I have no doubts.

Thank you!

[kumi]

MPEG2 default is BT.709
Hank315 (and others) believe that the MPEG2 (SD) default might in fact be Rec.601, not Rec.709: http://forum.doom9.org/showthread.php?p=1061536#post1061536.

@Merlin7777: So, if you take Hank315's position, you should be aware that dgmpgdec will signal the wrong colorimetry (Rec.709) when there is no explicit header specified in a MPEG-2 SD stream.

[Adub]

Ah crap.

Just when I thought I had it figured out. I guess the universal answer is to do a side by side comparison and determine which one looks "better".

[hkazemi]

I've compiled a summary to hopefully consolidate the threads and address the confusion over colorspace and the usage of Colormatrix. It is available at http://forum.doom9.org/showthread.php?t=133982#post1090068