Hi, I have a weird question. Someone recently told me that you could change a .tiff format to a .jpg format to "archive" the file, and then reopen the .jpg to unstuff it -- preserving all the original quality in the .tiff file.
This is pretty much the opposite of what I'd thought -- but the person who told me this is a graphics artist, so perhaps I have misunderstood what the .jpg format does to an image.
I had always thought that the .jpg format would continue to lose quality if reoptimized, etc - so it's best to utilize the 'high rez' (.tif) version of any image prior to saving as a .jpg.
Your understanding is correct - the current JPEG standard is "lossy" compression. Whenever you save as JPG, some quality is lost.
If storage space is a consideration (say, a location digital photo shoot) it is often worthwhile to save as low compression (high-quality) JPGs rather than TIFFs because of the enormous saving in storage space. But for most desktop use, stay with the TIFF or other lossless format as long as possible to save quality.
I work primarily in repro for magazine's, and with limited storage space if we were to keep every image as "raw" tif files we would soon run out of space. (ie we jpeg them).
It depends on the final destination of the image. Generally speaking you can take an A4 image (30+Mb as a tif) as wap it through a web-printing-press optimised as a jpeg on anything as low as 5 - depending on the colours of the image and paper-type / dot-gain.
It's reletively easy to pull an image back from extreme optimisation if ya know what your doing - but I would not recommend archiving anything below jpeg 5 if you want to keep shadow and midtone details and defintion between gradiants.
Oh yeah - I do all my optimising saving from Photoshop.
Yep, once you save it as a jpeg, you can never recover the data the jpg compressor "loses" when saving the file.
If you're low on storage space, you might consider saving groups of tif files together in compressed archives (.zip or .sit, etc.). You could group them by subject, or something like that, and then compress each group into one archive file, named by subject...
Or you could buy a CDRW drive and a couple spindles of CDR disks... they're getting cheaper all the time, and make a dandy archive format, as long as you store them carefully.
A tiff format can use LZW compression, which is lossless. Depending on the image involved, the savings in file size may be pretty good, or it may be minimal - but it's worth a try if you're saving a tiff for your archives.