[Digikam-users] re JPEG lossiness, PNG

[Paul Verizzo]

"I'm not sure if that's a rhetorical question. Anyway, I was doing some

changes on the images, and didn't want to lose more info due to the
jpg-compression.
I think of it this way (maybe I'm wrong): every time I change a jpg
image, some info of the origional gets lost and the image cannot ever
be put in the original state by just reverting the changes, because it
drops the original info and adds in some new based on the changes.
But (that's what I think) when I change a png image, I can get the
original state back by reverting the changes.
I knew that png makes the files bigger, but I still do not understand
how the jpg can become 10 times bigger by converting it to png. Even
the raw images of the same picture are less than half the size of the
png file.
I'll probably never fully understand the mysteries behind this,
because I can't even see the difference. I'll probably stick to jpg
even though some information is not stored in the file. Why don't
camera manufacturers use a non-lossy format that produces smaller
images than the raw images? Or isn't that possible at all?

Regards

Martin"
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Martin, you are correct about changing and saving JPEG files.  Oh, I wish I had known that a dozen years ago!  I manipulated many of my 2.1mp (!!) files, not understanding the consequences.  It was all pretty new back then, not many good maps for us digital Conquistadors!

Now that hard drive space is so cheap, the solution to this problem is simple: Save your original (RAW and/or post-RAW or out-of-the-camera JPEG's) files in a subfolder, possibly named, um, "Originals". Mark them all "Read Only."  Now you can manipulate to your heart's content and you always have an original to fall back on. 

I also save all files with 100% quality level, or whatever the "no compression" setting is for whatever program you are using.  Again, disk space is so cheap. 

PNG certainly should not be ten times as large as a JPEG. If you took a picture of an all monotone color, that would be maximum JPEG compression.  Every pixel is just like the others.  But I still can't imagine what would cause your issue. PNG is a nifty format with lots of potential and uses, but the not-lossiness isn't an issue if you save your originals as I've suggested. JPEG rules the jungle still, there is no downside as long as you don't keep working on, and then saving a file repeatedly.

I hope this helps a bit in your quest.

-- 
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith