[FFmpeg-devel] dcp encoding + new pixel format request/sponsorship

[Michael Bradshaw]

On Tue, Jan 22, 2013 at 1:12 AM, Reimar Döffinger
<Reimar.Doeffinger at gmx.de>wrote:

> On 21 Jan 2013, at 19:15, Michaël Cinquin <mc at michaelcinquin.com> wrote:
> > Hi
> >
> > I just sent my first pull request from my first commits on GitHub :
> michaelcinquin.com:master.
> >
> > The pull request is about adding an rgb2xyz av_filter, which enables the
> processing of colors for digital cinema, from sRGB colorspace to XYZ, based
> on a 3x3 color matrix. This will hopefully make FFmpeg more useful for DCP
> encoding.
> >
> > There is one last show-stopper for making FFmpeg the main tool of
> opensource DCP encoding.
> >
> > FFmpeg does not support saving to RGB 3x12 bpp formats : this means we
> cannot output the 12-bit files necessary for Digital Cinema. Without a new
> pixel format, one has to save TIFFs out of ffmpeg, then encode them to j2K
> with another tool, which as far as I know cannot be piped.
> >
> > Could I get help or sponsor the development of a new pixel format that
> will enable libopenjpeg to save 12 bips per channel J2K ?
>
> Is there any reason to add a 12 bit per component format instead of using
> the 16 bit one and telling the encoder it should discard 4 bit?
>

Out of curiosity, how would that work? Which 4 bits do you discard?
openjpeg itself can, in theory, save 12-bit RGB, but lavc would provide
frames in 16-bit RGB; simply discarding bits would give improper results. A
proper/scaling 16-bit to 12-bit conversion would need to be done, and it
hardly seems like the encoder is the right place to put that.

We also wouldn't be able to decode it without a 12-bit pixel format.

--Michael