On 2/13/2009 8:08 PM, David W. Fenton wrote:
They don't display the information, but PSP, at least (which is what I use for all my graphics editing -- I can't stand the GIMP), does not continue to compress the file beyond its current compression ration.
Except that I don't think PSP has any way of actually determining a file's current compression ratio.
Try it in PSP. I just took a file and saved it 6 times with compression set at 15%. When I compare the version saved 6 times to the original it is absolutely indistinguishable.
Were you closing and opening the file, or just hitting Save 6 times? The latter won't do anything, because each time you hit Save, PSP just compresses and writes out the bitmap it has in memory. And in the former case, the sources I have read do say that saving in the same app with the same compression ratio produces virtually no artifacts. And that artifacts would really only appear in areas you've edited, so that repeated opening and saving wouldn't be expected to show any degradation. But this whole conversation has been about editing files.
It's only the save process that discards data, and if you're saving back to the same compression ratio as the source file, you won't see any difference at all.
If you're saving back with the same application, at the same compression ratio, with no edits, then I suppose you're right.
It says that if you're saving at the same ratio, any loss is very tiny. My experience says that for all practical purposes, there is no loss.
I'm not disagreeing with you here. But "practical purposes" vary from user to user. The fact is that there *is* further loss, and the loss may be noticeable depending on the size of the source file, the compression ratio applied, and the users' eye.
I do note that the JPGs that I saved don't have the same file size:
Well, that in itself indicates that the files are not *strictly* identical.
Of course, I didn't actually do any edits, just saved the file.
Right. And as the articles point out, edited areas of the photo will show greater loss.
I think your concerns are overblown.
Quite possibly. I'm just pointing out guidelines for best and safest practice: Always save your master in a non-lossy format.
Aaron. _______________________________________________ Finale mailing list Finale@shsu.edu http://lists.shsu.edu/mailman/listinfo/finale
