h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

A quick word to the wise. If your camera stores images in the JPEG format and you want to do some editing with your photo-editing software (like removing red eye or mean old aunt Edna or whatever), do not work on the image in it's original file format. First save it as a Tiff or another noncompressed format (.psd in photoshop for instance). Everytime you open, make a change and save a JPEG you lose more data. It will recompress your already compressed file everytime it is saved. After only a few of these recompressions the artifacting and banding will become very noticable. If you first take the JPEG, open it with your software and IMEDIATELY "save as" a tiff you can then work on that tiff file as much as you like and never introduce more compression problems. Once you're done you can then save a copy in jpeg or whatever format you like for emailing or uploading or whatever. You'll still have your original camera file for archiving and your edited tiff file as well.

p.s. You can use the LZW compression for tiff files since this is a "lossless" compression method. They'll just take a little longer to open.

CZ

But, if you save as a jpeg at maximum quality of 12 in photoshop, it won't make very much change to the original file, so you can keep your file sizes down. Also, always save a copy of the camera original as archive with out any changes.

Yes it does... Every save recompresses the file even at maximum quality. If you are working in photoshop you should have no problem with large files anyway. When you are finished editing the file you can save it back to jpeg to save disc space. But do your work in a lossless format like .psd or .tif. If you don't have room to do this buy a larger harddrive. Storage space is cheap today.

Another alternative is jpeg2000 which is a lossless method, you need a plugin for photoshop for it, whilst it is OK for archiving it is not a popular format so not everyone will be able to open if you distribute files to others.
Most cameras now have a RAW file facility which saves all the information when taking the image, this allows for greater control of the final image which has to be converted to either jpeg or tiff.

A quick resize and levels edit won't do much damage to the average (640x480) screen based image.
In the Save For Web option in Photoshop, you can preview a magnified version of the final file.