Saving anything as a JPEG is going to alter the data in the file from the original when the compression is executed.
For many purposes the visible change in image quality may be insignificant after one save. People have done tests, there are literally thousands of posts on this forum discussing this matter.
As a general rule your approach is best only save as a JPEG if it is necessary for the end use. And always keep a copy of the original in its uncompressed form.
PSDs and TIFFs are generally usable in most applications nowadays as they are.
Thanks, John. Ya, that’s what I figured… but could someone answer my specific questions? I’m actually very curious about it from a technical standpoint.
but could someone answer my specific questions?
As I hinted, many hours of typing have gone into investigating and promulgating answers to your questions. If you can’t find answers here in the forum maybe someone will come along and open up the whole can of worms again.
It won’t be me. B)
Jpeg is a lossy format. that means every save throws mor data out. the more compression the more data loss.
1. No
2. No. but if you resave as jpeg you will have more loss. save as non lossy format.
3. Yes. Its the save that throws out more data.
4. Yes.
5. No. PSD or Tiff are best used for work files.
I ALWAYS use a lossless file format and only convert at the end for the web.
For instance, Flickr states that they will accept uncompressed files up to a certain size (for a paid account). I was uploading tiff files and kept noticing artifacts on the images. Come to find out they were converting my tiff files to jpegs and that was the issue. Now I upload a copy of the original file in jpeg format at 100% quality and no problem.
Buko: Thanks for that! One question, though… For #4, you said yes, which seems to contradict what you said for #1. For #4, I was asking that if I have an uncompressed file loaded, and then save as a 100% quality Jpeg, will it lose quality (or does 100% quality make it so it just looks for patterns/repetitions, without actually averaging out colours to increase the occurrences of that)? Did you mean to say no then?
Also, I’m curious why you prefer Tiff files? Smaller file sizes compared to Targas? I’ve been using Targas for delivery of broadcast fx shots for my whole career, but am certainly open to any other formats if they are superior in some way.
Harold: Ya, see that’s part of the reason I’m curious and am asking… because I have a feeling that combination of certain formats/compressors may cause problems. In AfterEffects, for example, loading footage with certain types of compression already present in the file causes the imported file to go corrupt (flash frames, breakup, etc)… So, I’m just trying to gain a better understanding of how it all works. I understand the basic concepts of compression (finding repetition/patterns), with (as I understand it) quality settings controlling how much it averages out the colours with the intention of creating more repetition (since then more colours would be the same)…. but I wasn’t sure if 100% averaged or not.
4) JPG is lossy. No, saving at 100% quality will not just find repetition and eliminate it, instead it WILL average colors and WILL damage the image. But at 100% quality, this damage is very minimal, and will be fine for print (and web, of course).
RE: Buko’s answer to #1 and #4. If he answered the same for those questions, then there would be a contradiction. The answers to #1 and #4 cannot be the same.
See answer #3 for the key answer to all questions. Image degradation occurs when the file is saved (during compression).
If you only intend to save a file once, JPG is not bad. The problem is that we rarely know for certain if we are done working on a file. We might need to open, edit and re-save many more times. Experiment with saving a file several times with minor modifications at 100% quality. If the results are tolerable, you can stick with JPG. Compression is all about tolerance. We tolerate compression on DVD movies, our DVRs, and digital television. But these are all end-formats. The content creators for this media start out with the best possible data (most often uncompressed).
The ‘I Love Lucy’ television show is an excellent history lesson on why we should start and archive with the best quality we can. Lucy can now be distributed in HD thanks to the forward thinking many years ago.
JPEG is not good for all kinds of print. For flexographic printing, even the minute artifacts of max quality compression could give horrible results. Such artifacts always have to be cleaned up.
You never know what your images may be repurposed for, or what fool will open your JPEG down the line to make edits and then resave it, not knowing any better. JPEGs for the web may be fine, but for print, there’s no reason not to use lossless formats.
for print, there’s no reason not to use lossless formats
I can think of a few. 🙂
The PDF/X-1a spec for printing allows for JPG image compression so someone in the printing world seems to think compression is not evil.
Cool… All good stuff. Ya, I guess I was being too cautious about jpeg use. As you suggest, I too don’t use jpeg (except for delivery from the master version, which is usually a PSD (for layered work), or a Targa. I just wasn’t really sure how badly the resaving would affect it, or if it brought with it some other issue (stability, chances or weirdness/artifacting when imported into some editor). Just was curious after all these years of being so cautious, just how extreme the degradation was, and (specifically) the compression worked (in relation to the quality settings).
Okay, I understand it a bit better now. Excellent. Thanks guys.
