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? _______________________________________________ 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".