> On 27 Sep 2017, at 14:20, Martin Vignali <martin.vign...@gmail.com> wrote: > > 2017-09-27 13:25 GMT+02:00 Tom Butterworth <bangno...@gmail.com > <mailto: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 >> <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 >> <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 ?
Personally I’d think 0 to allow further operations to eg combine the image with one with colour channels to work as expected. _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-devel
