2017-09-27 13:25 GMT+02:00 Tom Butterworth <bangno...@gmail.com>: > > > > On 27 Sep 2017, at 11:59, Martin Vignali <martin.vign...@gmail.com> > wrote: > > > >> > >>> + ctx->tex_fun = ctx->dxtc.rgtc1u_block; > >>> + avctx->pix_fmt = AV_PIX_FMT_RGB0; > >> > >> The rgtc1u_block function places the single channel value in every > channel > >> except the alpha channel > >> The pixel format you have chosen is one which disregards the alpha > channel > >> > >> The output of this alpha-only decoder should be in the alpha channel of > a > >> pixel format which carries alpha. Probably other channels should have > zero > >> values. > >> > >> > > Hi Tom, > > > > After Carl answer, and thinking about that, > > The goal of HapAlphaOnly, is to store alpha, but can also store gray only > > (much better than HAP) > > In fact, it can be call HAP Gray ! > > But it isn’t > > > For example from my part, i would like to use this codec, for matte, but > > also for gray only layer (use with color blending) > > This is fine, but let’s concentrate on supporting Hap Alpha Only, not your > non-standard use of it. If you would like this flexibility in Hap, that > should be argued for on the Hap project, not within FFmpeg. > > Hap Alpha Only is defined as an *alpha* channel stored in RGTC1U, and the > implementation in FFmpeg must follow the definition (see > https://github.com/Vidvox/hap/blob/master/documentation/HapVideoDRAFT.md < > https://github.com/Vidvox/hap/blob/master/documentation/HapVideoDRAFT.md> > ). > > The Alpha Only encoder and decoder must ingest and emit a pixel format > which carries alpha. It may be that adding a new alpha-only pixel format is > not seen as desirable, in which case an existing format with alpha should > be selected. This allows users to, eg, transcode from an RGBA format to Hap > Alpha Only and have the channel they expect be preserved from the input > video. Any other behaviour (eg having RGB converted to grey and then stored > as alpha) is not acceptable. > > > If a user want to compress a gray picture, it can be done using RGB to > Gray > > conversion > > And if user want to compress only alpha or a specific channel, i think > > ffmpeg have a filter for that (extractplanes (untested)), > > Your non-standard usage can still be achieved by channel switching in a > filter, the default behaviour must be according to the standard, which is > to encode and decode the alpha channel. > > Cheers - Tom > <http://ffmpeg.org/mailman/listinfo/ffmpeg-devel> >
Ok, in that case, the HAP Alpha Encoding current patch is fine (it take alpha from RGBA input) I will change the 24 to 32 as requested and send a new patch Before sending a new patch for the decoding : did you think, it's better to have [255,255,255, alpha] or [0,0,0, alpha] for RGTC1 alpha decoding in RGBA ? Martin _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
