[FFmpeg-user] Bad quality with ffmpeg's GIF encoder?

FFmichael michael.rampe at gmail.com
Mon Aug 30 10:18:11 CEST 2010



C. Sanchez wrote:
> 
> Hi!
> 
> First off, I know that GIF isn't really intended for >256 color images, 
> eg. photos. However, I sat down tonight messing around with a couple of 
> encoders, trying to see what they were able to produce. Now, this is my 
> results.
> 
> Original JPEG :
> http://i37.tinypic.com/14bothe.jpg
> 
> Transcoded into GIF with ImageMagick convert.exe :
> http://i33.tinypic.com/juuwaq.gif
> 
> Transcoded into GIF with imagine (Total Commander plugin) :
> http://i33.tinypic.com/sls5lk.gif
> 
> Transcoded into GIF with GIMP :
> http://i33.tinypic.com/30c67fb.gif
> 
> And now finally..
> 
> Transcoded into GIF with ffmpeg.exe :
> http://i35.tinypic.com/34y5vgw.jpg
> 
> <http://i33.tinypic.com/juuwaq.gif>I used the command:
> ffmpeg -i original.jpg -pix_fmt rgb24 output.gif
> 
> Funny thing also, I used an utility for color count on images. The 
> original JPG holds 70563 different colors, and all GIF's except for the 
> ffmpeg-generated holds 256 colors, i.e. the natural [one block] GIF 
> limit. The ffmpeg-generated file on the other hand, holds only 103 
> colors. This feels strange. Any suggestions? Am I missing out on some 
> command line syntax that strips all the quality, or is it something else?
> 
> Ty in adv~
> Gewie.
> 
I got exactly the same results when trying to replicate your issue.

Based on the info about only reporting 103 versus 256 colors, my guess is
that ImageMagick is using 256 indexed colors whilst FFmpeg is using a fixed
256 level system color palette. 

I confirmed this theory in Photoshop. I converting your original jpeg to
indexed color in photoshop. (Photoshop: Image/Mode/Indexed color...) By
using the local selection, the image is converted like ImageMagick. By using
the system or web selection (without diffusion), I get an image like FFmpeg.

Thus, FFmpeg is using a system color palette (or more likely a web palette)
in converting GIFs.

Michael
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