Sorry Jerry, I have to agree with some others that you are doing something wrong. JPEG compression does compound, and the image degrades further each time.
10D image, RAW to TIFF for editing and saved as JPEG one time, then "saved for web" at max quality (default of 80) :
 | HTTP response: NOT FOUND | MIME changed to 'image/gif' |
http://www.pbase.com/image/27017561
and 100% crop
| HTTP response: NOT FOUND | MIME changed to 'image/gif' |
http://www.pbase.com/image/27017562
(ooh, the scooter needs a dusting! but how 'bout that little star effect!)
Made an action to close the JPEG, reopen it, save as a JPEG with #12 quality in PS, close it, reopen it, lather, rinse, repeat 20 times, making this save #21:
| HTTP response: NOT FOUND | MIME changed to 'image/gif' |
http://www.pbase.com/image/27017564
Not bad, but you can already see compression artifacts, even at this size.
A 100% crop of #21:
| HTTP response: NOT FOUND | MIME changed to 'image/gif' |
http://www.pbase.com/image/27017566
The compression artifacts are pretty evident when zoomed in.
Now lets take a look at save #81:
| HTTP response: NOT FOUND | MIME changed to 'image/gif' |
http://www.pbase.com/image/27017567
Compression artifacts clearly visible. Looks bad.
A 100% crop of #81:
| HTTP response: NOT FOUND | MIME changed to 'image/gif' |
http://www.pbase.com/image/27017569
Honestly though, the result is better than I expected.
Also JPEG size DOES increase with repeated saves, as Jerry points out, but not by much. My #1 was 3365kb, my #81 was 3576kb. Something akin to high-ISO files being larger because of the added noise, I would guess. However, when one resizes for the web, the added "detail" (noise) makes a bigger difference, as my resized #1 was 101kb at maximum quality, while #81 ended up at 144kb.
