Re: JPG file size increases with saving

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]




Philip Rhoades wrote:
> What still doesn't make sense is that if the original file is JPG and
> one simply opens it and then saves it as another JPG file with 100%
> quality - you are saying that introduced artifacts are adding about 150%
> to the file size? (681 KB to 1.618 MB) How could the compression
> algorithms be so different as to cause this sort of result?  - At worst
> I would have expected maybe a 10% increase in size . .

well firstly, 1.6MB are not that bad in comparison to 9MB of raw RGB data, right?
(just try saving to uncompressed BMP as Greg suggested).

Btw, 100% quality for JPG gives very little visible advantage over the
default 90% setting.

The relationship between quality value, file size and perceived image quality
is very delicate. Any assertion has to be made with a lot of weasel words.
So yes, compression artifacts have a tendency to hinder compression,
resulting in larger file sizes after re-compression to comparable quality.
A similar effect is caused by noise. So to get optimal JPG files, it's
best to use a RAW->XCF->JPG workflow where the JPG is created only once.

Just have a look at the advanced settings in the JPG save dialog to get
a first impression of what machinery is at work here. There also was a
very long thread on gimp.developer on that very quality setting...


How does image quality compare if you adjust the quality slider
such that the resulting file size is about 680KB?


regards,
peter

_______________________________________________
Gimp-user mailing list
Gimp-user@xxxxxxxxxxxxxxxxxxxxxx
https://lists.XCF.Berkeley.EDU/mailman/listinfo/gimp-user

[Gimp Announce]     [Gimp Images]     [GIMP Development]     [Video For Linux]     [Photo]     [Yosemite News]    [Yosemite Photos]    [gtk]     [KDE]     [Scanner]     [Gimp's Home]     [Gimp Docs]     [Gimp on Windows]     [Steve's Art]     [Webcams]     [Share Your Images]     [Free Online Dating]     [Photo Site]     [Script Fu]     [GIMP Software]     [GIMP Books]

Barnes&Noble.com

Add to Google Follow Gimp on Twitter