On 8/1/17, Jon bae <jonba...@gmail.com> wrote: > 2017-07-31 22:16 GMT+02:00 Paul B Mahol <one...@gmail.com>: > >> On 7/31/17, Jonathan Baecker <jonba...@gmail.com> wrote: >> > >> > >> > 2017-07-31 14:41 GMT+02:00 Paul B Mahol <one...@gmail.com >> > <mailto:one...@gmail.com>>: >> > >> > On 7/31/17, Jon bae <jonba...@gmail.com >> > <mailto:jonba...@gmail.com>> >> > wrote: >> > > 2017-07-31 14:00 GMT+02:00 Paul B Mahol <one...@gmail.com >> > <mailto:one...@gmail.com>>: >> > > >> > >> On 7/31/17, Jon bae <jonba...@gmail.com >> > <mailto:jonba...@gmail.com>> wrote: >> > >> > 2017-07-31 10:30 GMT+02:00 Paul B Mahol <one...@gmail.com >> > <mailto:one...@gmail.com>>: >> > >> >> >> > >> >>> >> > >> >>> What exactly you tried? >> > >> >>> >> > >> >>> Perhaps you want premultiply filter? >> > >> >>> >> > >> >>> Yes I have a video and a lower third, and I want to overlay >> > the lower >> > >> >> third. But my alpha channel from the lower third is not >> > pre-devided >> > >> >> with >> > >> >> the alpha channel, so I need to do a channel division in >> > ffmpeg. >> > >> >> Something like: >> > >> >> >> > >> >> ffmpeg -i video.mp4 -i lowerthird.png -filter_complex >> > >> >> [1:v]geq=r=r/a:g=g/a:b=b/a[gq];[0:v][gq]overlay ... >> output.mp4 >> > >> >> >> > >> >> I see that you wrote a filter for this, but can you please >> > give me an >> > >> > example of how it works? I don't get it to run. >> > >> >> > >> "I don't get it to run" means nothing to me. >> > >> >> > >> I'm not sure if I use the filter correct... But with this: >> > > >> > > ffmpeg -i video.mp4 -i image.png -filter_complex >> > > "[0:v]format=rgba[a];[1:v]format=rgba[b];[a][b]premultiply" >> > > >> > > My result is, that everything what had alpha = 0, in my image, >> > is >> > now >> > > black. Mybe I understand the use case wrong, but how you would >> > use this >> > > filter? >> > >> > Try harder to explain your use case? >> > >> > Sorry, my english is not so good, but I will try it. In the attachment >> > you found 3 images. Universum.png is my original lower third, it comes >> > out from blackmagic fusion. Universum-comp.jpg show the composite of a >> > background video with the lower third, this is the correct result. The >> > Universium-ffmpeg is the version from ffmpeg, as you see ffmpeg handles >> > the alpha channel different so the lower third is more dark. >> > >> > I can simulate the same effect, from ffmpeg, in my compositing program, >> > when I load the lower third image with the option "Post-Multiply by >> > Alpha". I guess this is what ffmpeg does in Background, when it load >> > images with alpha channel. >> > To get rid of this effect now in my composition program I have to >> > divide >> > the color channel from the lower third with its own alpha: >> > red/alpha;green/alpha;blue/alpha. Now I can overlay the lower third and >> > the result is correct. >> > >> > This division now I would need in ffmpeg. I though I can do it with >> > your >> > premultiply filter, but maybe not. >> >> Perhaps you want overlay filter? >> > > No the overlay filter don't handle the alpha channel correct, that is what > I was trying to say. > > You can try it by your own - get this 3 images and run this command: > > ffmpeg -loop 1 -f image2 -i backgroud.png -i multiplied-alpha.png > -filter_complex overlay -pix_fmt rgb24 -f sdl "multiplied alpha" > > ffmpeg -loop 1 -f image2 -i backgroud.png -i pre-divide-alpha.png > -filter_complex overlay -pix_fmt rgb24 -f sdl "divide alpha" > > The second one overlay the image correct. The first one overlay the image > different, because the alpha channel is not the same. >
I stll do not know what you are trying to tell me. Do you have equatition how should R/G/B be calculated with Alpha? _______________________________________________ ffmpeg-user mailing list ffmpeg-user@ffmpeg.org http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email ffmpeg-user-requ...@ffmpeg.org with subject "unsubscribe".
