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This is probably the same question as https://www.reddit.com/r/kdenlive/comments/ik44o2/image_sequences_cutting_and_transparency/ ( and probably related to https://kdenlive.org/en/project/compositing-with-transparency/ )

Let's say I have an image sequence, with transparent background, and an element (here a rectangle) with a fill color with fading alpha/transparency; for instance, one generated with imagemagick:

for ix in `seq 1 9`; do \
  convert -size 640x480 xc:none \
   -strokewidth 0 -fill "rgba( 255, 215, 30, 0.$ix )" \
     -draw "rectangle 30,30 500,250" \
   -strokewidth 2 -stroke blue -fill none \
   -draw "rectangle 0,0 639,479" output$ix.png; \
done

It is very difficult obtaining a proper .gif animation directly from the above images; so I opened each one in an image viewer, took screenshot of the image viewer, and finally composed the screenshot images with convert -delay 0 -loop 0 Screenshot*.png animation_im.gif, just to show what this image sequence looks like:

image sequence animated gif via screenshots

The animation above shows that there is a "gradual" or "continuous" "fade" of the color via the alpha channel.

Now, the problem is - typically, if I import this image sequence in kdenlive (kdenlive-23.04.0-x86_64.AppImage), and I render a video - the gradual fade is gone/disappears, and the only thing I get is a sudden/instantaneous appearance of the rectangle; similar to output of convert -delay 0 -loop 0 output*.png animation_im.gif (ran on the original image sequence):

animated gif from original image sequence

So, my question is: how do I preserve an alpha/transparency gradual/continuous fade in an image sequence, also in the rendered video output of kdenlive?

1 Answer 1

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Well, discovered this almost by accident - but it turns out, to preserve the alpha gradual fades, you MUST add Composite and transform: Composition track: automatic; Compositing: Alpha blend, for the duration of the image sequence:

kdenlive image sequence video track with Composite

... - even if the image sequence is the only track (so compositing then works against the background)!

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