sallyanne wrote:
rich2005 wrote:
If the files are already compressed, jpegs, gimp xcfgz, there will not be much gain. .
Does that mean if I make the file smaller when saving it in gimp (png's), they will not compress much more?
New day,
finally got round to making some comparisons
Using the same image in different formats, and 7zip with best compression.
First a jpeg, which of course is already 'lossy' compressed,
jpg file size 417K 7zip 418K - this is the compressing an existing compressed file effect, the file is larger.
Next the png, but exported with a compression value = 0
png file size 1.4M 7 zip 1.1M - about 20% reduction
Then the png exported with Gimp default compression value = 9 (the maximum)
png file size 1.2M 7zip 1.2M - actually a 1% increase in size.
Where you get economies with these file formats, is archiving lots of small files, (late edit: into one single 7zip file) this is stored more economically on disk. Beware, if you rely on this for saving disk space, one day sooner or later you will make a mistake and lose the lot. Archive as a backup only, and keep two or three copies on different disks.