Several of the fairly popular digital cameras have used proprietary file formats as their default for saving the pictures, but .jpg is pretty much the accepted format among pro/am and professional users, and most cameras can be reset to save as .jpg. If you really want all the bits, the high-dollar cameras allow you to save as .bmp, but the files can be huge. Saving as .bmp is the only format that recovers and saves "everything that the camera recorded."

Many cameras allow you to choose a "normal" .jpg, with considerable compression, or a "hi-res" .jpg which has little compression. The difference with my wimpy little 2 MP camera is 32 KB for the normal and about 700 KB for the hi-res. The 32 KB should print quite nicely at snapshot size, 4" x 6" or so, and makes "passable" 5 x 7 prints without additional "workup," but you do need more pixels for larger prints. In theory, the hi-res 700 KB should make a "reasonably good" print (72 dpi on the paper) up to about 16 x 22 inches with no (or very little) editing. (With a little work, a 300 KB .jpg can usually be "worked up" to print at 600" x 900" or larger, but who needs that may billboards? Blowing up to this scale to extract a small detail is another matter, though.)

The .png file format is not the Kodak one that I'd had problems with, so I apologize for the misidentification. It's a format that was developed to replace the .gif compression, and is apparently a pretty good format with respect to picture fidelity, but does appear to have some problems with portability between programs. The only "living major" application that's really equipped to handle it (based on my look at the list at the PNG website) is CorelDraw!. Canvas and a couple of "PhotoDraw" (bundled editing programs) used it and died. Like .jpg, you can choose a compression level (in some programs) and if you choose to not recompress you could make repeated saves without losing addional pixels. If you recompress at each save, I would expect losses similar to those with .jpg, although that may not be quite a "true picture" of the format's abilities. The original conversion to .png may, or may not, truncate pixel information, depending on program and settings.

If you're starting with a digital photo or scan, the original conversion to .gif truncates the picture information, and discards a lot of it. Once converted, you don't lose additional information when you re-save, but it's not a good format to use during editing. Create a .gif from your final "good" file only when you need a .gif for a specific end use.

There are too many "kinds" of .tif files to make sweeping statements, but some .tif conversions discard data during the original conversion to .tif, but (usually) everything saved in the first .tif is saved through subsequent re-saves.

If you save at "hi-res" (no compression) levels, .jpg files can be re-saved repeatedly with very little, if any, loss; but the majority of "consumer level" graphic editing programs don't give you the choice. The advice to use a "lossless" format should stil be followed unless you know that the losses, with your program and settings, are acceptable for your purposes. For working in PS or PSE, one would use either the program's native .psd or .bmp while you want to keep all the image information intact.

John