[Gambas-user] Image.Save resp. Picture.Save Method

Claus Dietrich claus.dietrich at freenet.de
Tue Sep 7 15:30:07 CEST 2021

I investigated the subject roughly on the surface with the pngcheck-tool and found:

The Quality-parameter of the Picture/Image.Save-Method maps to following PNG-compression
methods (the achieved compression refers to a typical printed letter page):

Quality   Compression
10        maximum compression (91.2%)
20        maximum compression  (91.1%)
30        default compression (91.1%)
40        fast compression (91.1%)
50        fast compression (91.0%)
60        fast compression (90.6%)
70        fast compression (90.5%)
80        superfast compression (90.4%)
90        superfast compression (-0.2%) - no compression
non       superfast compression (-0.2%) - no compression

I didn't investigate yet what happens at quality levels i.e. of 71 to 79. Whether the
compression terms "maximum comression", "default compression" etc. are the only ones
applied for PNGs and why the "fast compression" between 40 to 70 provided sligthly
different values is unknown to me. Does anybody have an idea?

> My answer will be fast ... I don't know :-)... but I suspect you're
>true about the mapping

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