[Digikam-users] png huge

[Martin Senftleben]

Hi

I have another thing that puzzles me: I've set digikam to store images 
as png, and always wonder how or rather why it makes out of a 2 MB jpg 
file a 10 MB png file, even though the png compression is set to its 
highest rate. Does png mean to increase file size by 5? Where does the 
additional info, that couldn't be in the jpg file, come from?
Please point me to the place where this is explained, in case it has 
been done already. I didn't find anything. Only the usual: jpg does 
lossy compression, png doesn't. 
But I see it maybe too simple: The jpg file has a limited amount of 
info - uncompressed in a sense, because it's the original from which 
the png file is made. The png file now takes this info and then gets 
compressed to the maximum possible - yet it's 5 times larger.

Do I see that right, or am I completely on the wrong track?
When I make well readable screenshots e.g., the file size in png is 
minimal (just a few kB), yet the image looks crisp and clear. So png 
can be small, it doesn't have a tremendous overhead.

Any help in understanding this will be apprecieated.

Martin
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