[Ffmpeg-devel] PIX_FMT_RGB555 and alpha channel

[Michael Niedermayer]

Hi

On Mon, Oct 30, 2006 at 02:48:06AM +0100, Alex Beregszaszi wrote:
> Hi,
> 
> > > I will elaborate.  Alex and I are implementing FLC/FLX and DTA
> > > encoding  into ffmpeg.  We are a little way from having stuff ready
> > > to submit, but  there is a problem with compression when the Alpha
> > > bit is set in an  RGB555 pixel, for the FLX format.  It means we
> > > have to mask every pixel  coming in, to take the spurious alpha bit
> > > out, or that bit prevents run  length compression from being
> > > effective.  The format is really wanting  to use RGB555, without
> > > alpha, so that black is 0x0000 and not 0x8000 but 
> > 
> > why does RLE compression not work with the alpha bit set?
> > and why exactly is the alpha bit set at all? if imgconvert.c sets it,
> > IMO fix imgconvert.c so it doesnt
> 
> Attached is a patch which fixes it, and adds the old behaviour as
> RGBA555.

rejected as already said, i wont accept a second native endiam rgb555
format to avoid a _single_ instruction in a very old and obscure codec


[...]
> Index: libavutil/avutil.h
> ===================================================================
> --- libavutil/avutil.h	(revision 6738)
> +++ libavutil/avutil.h	(working copy)
> @@ -78,7 +78,8 @@
>      PIX_FMT_YUV410P,   ///< Planar YUV 4:1:0,  9bpp, (1 Cr & Cb sample per 4x4 Y samples)
>      PIX_FMT_YUV411P,   ///< Planar YUV 4:1:1, 12bpp, (1 Cr & Cb sample per 4x1 Y samples)
>      PIX_FMT_RGB565,    ///< Packed RGB 5:6:5, 16bpp, (msb)   5R 6G 5B(lsb), in cpu endianness
> -    PIX_FMT_RGB555,    ///< Packed RGB 5:5:5, 16bpp, (msb)1A 5R 5G 5B(lsb), in cpu endianness most significant bit to 1
> +    PIX_FMT_RGB555,    ///< Packed RGB 5:5:5, 16bpp, (msb)1A 5R 5G 5B(lsb), in cpu endianness most significant bit to 0
> +    PIX_FMT_RGBA555,    ///< Packed RGB 5:5:5, 16bpp, (msb)1A 5R 5G 5B(lsb), in cpu endianness most significant bit to 1
>      PIX_FMT_GRAY8,     ///<        Y        ,  8bpp

breaks binary compatibility

also it likely breaks the swscaler as you didnt change it

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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