[MPlayer-dev-eng] best colorspace to look for black frames

[Fredrik Kuivinen]

On Wed, Apr 24, 2002 at 03:57:28AM -0400, Brian J. Murrell wrote:
> OK, in case you didn't realize it I am pretty new to this video stuff.
> I don't really understand all the many differences regarding
> colorspaces.  I understand the basics (i.e. YUV vs. RGB) but there
> seem to be so many choices with MPlayer.
> 
> So I am wondering two things.
> 
> 1) Which colorspace would be easiest for determining if a pixel is a
>    certain amount of black (i.e. between a specific shade of grey and
>    pitch black) and
> 

YV12 will probably be quite simple to use. The Y component is the
"brightness". Extracting brightness information from the RGB formats
isn't very hard either.  

> 2) How can I figure out how to extract the color information for a
>    given pixel from the "plane(s)" in the mp_image_t * returned by
>    vf_get_image()?  I think I have determined that RGB colorspaces use
>    3 planes for each pixel (one plane each for R, G and B) and YV12
>    uses only the one plane with the YUV values packed into it, but in
>    what format, I dunno.
> 

The RGB formats are all packed which means that everything is in one plane. 
YV12 is a planar format with three planes, Y, U and V.
Y is the "brightness" U and V contains color information. 

> Is there anywhere I can read about this stuff, especially as MPlayer
> has implemented it?

DOCS/tech/colorspaces.txt, http://www.webartz.com/fourcc/ and
http://www.inforamp.net/~poynton/ColorFAQ.html

/ Fredrik