On Fri, Jan 15, 2010 at 5:54 PM, David Hodson <hods...@ozemail.com.au> wrote:
> On Fri, 2010-01-15 at 13:32 -0600, Paul Hartman wrote:
>> On Fri, Jan 15, 2010 at 12:27 PM, Philip Rhoades <p...@pricom.com.au> wrote:
>> > - when the JPG is uncompressed by GIMP into RAM, there is no loss of
>> > information (?)
>> Since JPG is not lossless, there is always a loss of information. Or
>> more specifically the same JPG can be interpreted differently by
>> different software, so opening it in GIMP might look different than
>> another program perhaps.
> I'm fairly sure this is not true - there is only one way to uncompress a
> JPG file, so all programs should create the same uncompressed version.

>From an old JPEG FAQ:

"Another important aspect of JPEG is that decoders can trade off
decoding speed against image quality, by using fast but inaccurate
approximations to the required calculations.  Some viewers obtain
remarkable speedups in this way.  (Encoders can also trade accuracy
for speed, but there's usually less reason to make such a sacrifice
when writing a file.)"

Also, of course, things like color management and other kinds of
post-processing can cause differences when the same file is opened in
different programs.
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