Duplicate an image with no Alpha to the same image with Alpha.

Questions involving a Windows version of FFmpeg.
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WexTwoTwo
Posts: 3
Joined: Mon Apr 22, 2019 10:25 pm

Duplicate an image with no Alpha to the same image with Alpha.

Post by WexTwoTwo » Mon Apr 22, 2019 10:38 pm

Hello all,

I'm looking to duplicate one image that is missing alpha channel and just duplicate it while adding an alpha channel to the image.
I"m guessing it might come out black as when multiplying the channels, and there is no alpha channel and than adding one, the conversion will come out black.

But... any-ways... I kinda need it.

So here is what I have tried and failed.... a few things I tried.

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ffmpeg3 -y -i noAlpha.tif -pix_fmt rgba -vcodec tiff -frames:v 1 withAlpha.png

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ffmpeg3 -y -i noAlpha.tif -pix_fmt rgba -vcodec tiff -t withAlpha.png

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ffmpeg3 -y -i noAlpha.tif -pix_fmt rgba withAlpha.png
Yeah, I"m just not sure how to set it, how to make ffmpeg convert image to image, not a video.
My source image(noAlpha.###) could be .exr / .tif / .png, the output, I'm writing in a way that it will be as the noAlpha.### source.

I could not find alot of docs' with images alone, most of it is videos.
Any help will be... amazing!

Thank you.

pandy
Posts: 184
Joined: Mon Feb 24, 2014 1:46 pm

Re: Duplicate an image with no Alpha to the same image with Alpha.

Post by pandy » Sat Apr 27, 2019 9:44 am

Seem alpha is not particularly easy in ffmpeg (at least not intuitive) - i was able to make it work somehow with example bellow:

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@ffmpeg.exe -hide_banner -v 32 -stats -strict -1 -i %filename% -an  -filter_complex "[0:v]scale=773:439:sws_flags=spline+accurate_rnd+full_chroma_int+full_chroma_inp:interl=-1:out_range=full,pad=1920:1080:990:224[a0];movie=bg.png,premultiply=inplace=1[b0];[a0][b0]overlay=0:0:alpha=premultiplied,scale=960:-2,format=pix_fmts=yuv420p" -c:v ffv1 -vsync 0 -f NUT - | ffplay.exe -hide_banner -loglevel 32 -autoexit -i -
I think you must explicitly call alpha channel and explicitly use it - command premultiply seem do the job - you need to modify this command to your needs but it should be relatively straightforward - ffmpeg pipe to ffplay so you can see on screen effect of video processing. Also remember on quantization range (in past i think ffmpeg failed on this, perhaps now it is improved - i mean YUV<>RGB converssion).

WexTwoTwo
Posts: 3
Joined: Mon Apr 22, 2019 10:25 pm

Re: Duplicate an image with no Alpha to the same image with Alpha.

Post by WexTwoTwo » Mon Apr 29, 2019 7:03 pm

I"ll take alook later this week.

Thank you so much for the reply

WexTwoTwo
Posts: 3
Joined: Mon Apr 22, 2019 10:25 pm

Re: Duplicate an image with no Alpha to the same image with Alpha.

Post by WexTwoTwo » Tue May 07, 2019 12:23 am

We ended up doing and using something else.
We used oiiotool for this.

Thank you for the reply

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