[Ffmpeg-devel] Color to grayscale switching

Erik Slagter erik
Tue May 31 13:05:29 CEST 2005

On Tue, 2005-05-31 at 11:22 +0200, Mathieu Minard - LABRI wrote:

> > > i have implemented a function that removes chroma planes from YUV420P
> > frames. I
> > > have done this by setting all chrominances values (UV) to the value 128.
> > Now i
> > > wonder why it doesn't lead to smaller output file size?
> >
> > Maybe the bits are spent to luma--and they definitely are if you used
> > rate control. Did you get PSNR increase in luma?
> OK, thank you. In fact, the rate control was set to 200 kbps. If i raise it, i
> obtain a bit smaller file size. Nevertheless, i would have expected a more
> important reduction.

I'd say that the only sensible way to test this, is to specify a
constant qp, not a bitrate. Or specify the bitrate and observe the qp
per frame.

BTW there is a parameter to make libavcodec encode only greyscale, but
I'm not sure it's a ffmpeg parameter.

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