Philip Rhoades wrote:
Cristi,
On 2010-01-16 06:55, Cristian Secară wrote:
On Fri, 15 Jan 2010 21:56:40 +1100, Philip Rhoades wrote:
- When saving as JPG with 85% quality am I losing information?
Yes, but still with the same 85% quality you may obtain different
results by changing other parameters.
Just look at the following example. Note the file size for each, but
most of all, look at the color quality and the outline of objects
(the files are quite small; save them somewhere and look at them by
switching forth and back so you can notice the differences).
The JPEG were both saved with 85%, but one with subsample for best
quality and the other with subsample for minimum file size:
http://www.secarica.ro/misc/monopoly.bmp
http://www.secarica.ro/misc/monopoly.png
http://www.secarica.ro/misc/monopoly_gimp_hi_quality.jpg
http://www.secarica.ro/misc/monopoly_gimp_minim_size.jpg
Take the .bmp and do further tests with the save options.
Yep, the only one where I could see a difference was with the last one.
It still seems counter intuitive that opening a JPG (even if it is a
photo rather than a computer generated image) and immediately saving it
with 100% "quality" increases the size by 2.5 .
The exampe image is actually not well-suited for JPG. For this one,
indexed PNG would work much better. Som, this comparisonis actually
misleading. It would actually be better use a photo for this.
When I was still using Windows (I'm under Ubuntu "Karmic" now), I used
Ulead's SmartSaver, where one can view the original & the optimized image
at the same time and tweak the settings until one is satisfied with the
result.
I usually have compression set to '90%'. Due to quality reasons, I never go
below that. Additionally, for DCT (Discrete Cosinus Transformation), I am
using 'Fast Integer', not 'Floating Point' (further loss, AFAIK). ('DCT'
is part
of the JPG compression process, which works in several steps.)
Claus
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