[Cin] oops apparently 'subtract' mode is broken!

Andrew Randrianasulu randrianasulu at gmail.com
Thu Sep 29 21:24:03 CEST 2022

чт, 29 сент. 2022 г., 20:00 Andrew Randrianasulu <randrianasulu at gmail.com>:

> чт, 29 сент. 2022 г., 19:21 Andrea paz <gamberucci.andrea at gmail.com>:
>> may be because 100 - 100 in alpha channel = 0 ?
>> Yes, I think so.
> also, because default png render both for ffmpeg and native NOT using
> alpha channel - be sure to select rgba format for ffmpeg and check alpha
> checkbox for png ....
> I tried to render with native png and initially result loads/shows up in
> resources wrongly because it uses just png not png alpha (?) yet loading
> same png standalone via ffmpeg shows up alpha in image correctly ....

this is confusing!

I tried to load resulting rgba png in GIMP and then it showed wrong too,
until I deselected alpha channel visibility!

so, it seems
ffmpeg's image decoders just drop alpha currently. from images at least.

native cinelerra's decoders correctly route alpha, but we can't see it
correctly on resources or on tracks...

compositor apparently  just drop alpha in rgba project mode, so we see only
color components from composited image. But alpha channel still around and
get rendered into image formats with alpha. And rendering into images
without alpha may result in black image in at least subtract mode because
alpha subtracted too, and this affect actual image?? like rgba -> rgb
transfer with alpha =0 just result in blank black image??

this adds some confusion!!

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