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Add stats_mode=diff and diff_mode=rectangle

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`stats_mode=diff` makes `palettegen` focus on the changes between frames instead of the whole frame.
Given that the whole frame (usually) consists mainly of a static white background, this is likely to improve image quality

`diff_mode=rectangle` makes the gif encoding crop to the bounding box of the changing parts. This again is likely to improve image quality because it avoids error diffusion to parts of the image that do not change. It can also greatly reduce file-size for GIFs where only a small section of the image changes between frames.

See this comment for more details: 

https://github.com/JuliaPlots/Plots.jl/issues/423#issuecomment-342173040
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Job van der Zwan 2017-11-06 17:31:01 +01:00 committed by GitHub
parent ab29a712c0
commit e87d7ef776
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1 changed files with 4 additions and 2 deletions
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6
src/animation.jl
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@ -72,9 +72,11 @@ function buildanimation(animdir::AbstractString, fn::AbstractString,
if is_animated_gif
# generate a colorpalette first so ffmpeg does not have to guess it
run(`ffmpeg -v 0 -i $(animdir)/%06d.png -vf palettegen -y palette.png`)
# use stats_mode=diff to emphasize changes and avoid bias for static white background
run(`ffmpeg -v 0 -i $(animdir)/%06d.png -vf palettegen=stats_mode=diff -y palette.png`)
# then apply the palette to get better results
run(`ffmpeg -v 0 -framerate $fps -loop $loop -i $(animdir)/%06d.png -i palette.png -lavfi paletteuse -y $fn`)
# use diff_mode=rectangle to improve rendering quality and reduce file-size
run(`ffmpeg -v 0 -framerate $fps -loop $loop -i $(animdir)/%06d.png -i palette.png -lavfi paletteuse=diff_mode=rectangle -y $fn`)
else
run(`ffmpeg -v 0 -framerate $fps -loop $loop -i $(animdir)/%06d.png -pix_fmt yuv420p -y $fn`)
end