No subject

Wed Apr 17 13:17:15 BST 2019

[TestDBThumb]$ du -c *-q100.jpg
68K     01-q100.jpg
52K     02-q100.jpg
124K    03-q100.jpg
56K     04-q100.jpg
72K     05-q100.jpg
56K     06-q100.jpg
88K     07-q100.jpg
84K     08-q100.jpg
84K     09-q100.jpg
116K    10-q100.jpg
800K    total

[TestDBThumb]$ du -c *-q85.jpg
16K     01-q85.jpg
12K     02-q85.jpg
36K     03-q85.jpg
12K     04-q85.jpg
16K     05-q85.jpg
16K     06-q85.jpg
28K     07-q85.jpg
20K     08-q85.jpg
24K     09-q85.jpg
36K     10-q85.jpg
216K    total

[TestDBThumb]$ du -c *.jp2
72K     01.jp2
52K     02.jp2
128K    03.jp2
72K     04.jp2
76K     05.jp2
64K     06.jp2
116K    07.jp2
84K     08.jp2
84K     09.jp2
148K    10.jp2
896K    total

[TestDBThumb]$ du -c *.pgf
76K     01.pgf
56K     02.pgf
132K    03.pgf
80K     04.pgf
76K     05.pgf
68K     06.pgf
104K    07.pgf
88K     08.pgf
88K     09.pgf
124K    10.pgf
892K    total

[TestDBThumb]$ du -c *.png
84K     01.png
60K     02.png
144K    03.png
84K     04.png
96K     05.png
76K     06.png
128K    07.png
108K    08.png
104K    09.png
168K    10.png
1,1M    total

Tests have been performed using 10 different photos from my
collections. Image sizes are 256x256 (a real rectangle with image
PNG files are generated with ImageMagick from bmp reference images.
There is _no_ metadata in PNG (pure image)
This point is important, because with my previous tests, i have use
PNG file generated from JPG with a lots of metadata. For small images,
this is not valid because metadata are large.

Files Generated are :

- JP2 (JPEG2000) in lossless
- PGF in lossless (quality=0)
- JPG with quality = 100 ("-q100" : not lossless but at least the best quallity)
- JPG with quality = 85 ("-q85" : the default value used everywhere
IM, gimp, photoshop, etc.)

JPG quality 85 is the best. Gain = 5
JPG quality 100, PGF and JP2 give the same size. Gain around 1.3.

Of course, we can use PGF and JP2 compression level not lossless. file
size will be decreased, but what will be the gain here against JPG in
this case ?

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