[Image-SIG] Subsampling in Thumbnail Mode for Jpeg files..?

Andreas Schmidt java.jago at gmail.com
Thu Jul 27 12:31:10 CEST 2006


Sorry, I have a couple of questions:

1.  When I create a thumbnail with PIL it is extremly fast! Is this speadup
due to the subsampling (using only the DC component) alone ? Or are there
some other tricks ?

2. In thumbnail-Mode - does PIL still read the full jpeg stream from disk
and then only reads the Bytes of the DC component ? Or does PIL directly
read less Bytes from the disk, i.e. only the Bytes of the DC component ?
How does it "know" which Bytes belong to the DC component ?

3. I guess 1/8 is the limit for subsampling since 8x8 blocks are used and
PIL is taking only the DC component is that case ?

4. What tricks is PIL using to speed up Thumbnail creation ?

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