[Cin] possible alpha bug in processing

[Phyllis Smith]

Yes, seems to be a problem, but I have no idea what the repercussions of
the patch would be based on the following in the  release notes for
September 2020 which says in the Bugs/Issues fixed:
  "Alpha is being set to 1 for background color always now – just a missing
thing."

On Fri, Nov 11, 2022 at 5:31 AM Andrew Randrianasulu <
randrianasulu at gmail.com> wrote:

> User 'goat' reported cingg failed to create png sequence with alpha, even
> if proj set to rgba and png settings also include alpha.
>
> I ..spend a lot of tume in filepng and fule, until it dawned at me Ican
> check older cingg!
>
> Bug was not there in june 15 2020  selfbuild.
>
> And bug was present in 09 30 2020 ubuntu 16 static tar ...
>
>
> So I searched git log and found this commit
>
>
> https://git.cinelerra-gg.org/git/?p=goodguy/cinelerra.git;a=blobdiff;f=cinelerra-5.1/cinelerra/virtualvconsole.C;h=3c3fb86f5710e15954c927f358210027cb819ed1;hp=193761b6763a61d11b0b85c8edbb4ec658df2b99;hb=abdff69b9309c7d5cd2ed6ce17dd2e0d85aef9a1;hpb=0b751b07a28e84a721b2bb76083db6629aa26d73
>
>
> i tried to set alpha to 0 (zero) in virtialvconsole and suddently pngs and
> exrs and tgas got their alpha back!
>
>
> How to check:
>
> Load video into cingg
> Set format to rgba-8 bit
> Set Alpha plugin over video, with parameter 0.5
> or use fader.
> Set output render to one frame, png, use alpha.
>
> Render
>
> While image will be  with right format alpha will be absent as evidenced
> by gimp's colorpicker.
>
> patch cingg with attached patch, hope alpha will be back!
>
>
> But of course we better to re-test video formats with alpha too ... (just
> not sure how)
>
> note, ffmpeg's png encoder worked ok, and so did tiff encoder. But
> png/exr/tga were all busted wrt alpha.
>
>
>
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