JPG file size increases with saving

[Philip Rhoades <phil@xxxxxxxxxxxxx>]

People,

I am trying to work out why there is such a large file increase when I 
edit a file and save it.  The background info:

Original file (from digital camera) - format, size, depth, geom:

JPEG   680590   8     2048x1536

After opening and saving original file with defaults (85% quality):

JPEG   646554   8     2048x1536

After opening and saving original file with defaults but with 100% quality:

JPEG   1618121   8     2048x1536

After opening, cropping and saving original file as a PNG file with 
defaults (compression 9):

PNG   4722953   8     2048x1536

After opening, cropping and saving original file with defaults but with 
100% quality:

JPEG   1631911   8     1590x1332

Questions:

- When saving as JPG with 85% quality am I losing information?

- How can saving as JPG with 100% quality increase information (file size)?

- Why is PNG so inefficient?

- imageinfo doesn't seem to be able to indicate information structure 
/compression information differences between the files - is there some 
way of doing this?

Thanks,

Phil.
-- 
Philip Rhoades

GPO Box 3411
Sydney NSW	2001
Australia
E-mail:  phil@xxxxxxxxxxxxx
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