yahvuu wrote:
Norman Silverstone wrote:
Here is a table that provides an approximate mapping between Photoshop
quality levels and GIMP (actually IJG JPEG library) quality levels:
Adobe Photoshop quality 12 <= GIMP quality 98, subsampling 1x1
Sure; subsampling takes groups of 4 x 4 pixels and averages the values
for hue/lightness for 2 x 2 pixels, or all four pixels respectively.
4 x 4 x 4 retains the original data, 4 x 2 x 2 averages for two groups
of 2 pixels each, and 4 x 1 x 1 assigns the same value to all four pixels in
the group , which results in a smaller file, but loss of quality at the same
time. (That's at least how I understood it.)
4 x 4 x 4: 4 x 2 x 2: 4 x 1 x 1:
--------- --------- ---------
| | | | | | | |
--------- | | | | |
| | | | | | | |
--------- --------- ---------
Then there' s also the DCT value (Discrete Cosinus Transformation; the
algorithm used in JPEG; I think JPG 2000 uses a Discrete Wavelet
Transformation instead, which results in better quality -> less JPG
artifacts). I have set this option to 'Fast Integer'; 'Floating Point'
results
AFAIK in additional loss of information.
Claus
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