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Digital Photo Processing
Resave Original JPGs as TIFs or PNGs
SUMMARY: If you are planning on editing a JPG photo, immediately resave it as a TIF or PNG file first.
As mentioned elsewhere on MalekTips, before editing digital photos, save the originals! This way if you overwrite the original file with your edits and decide later that you do not like the result, you can revert to the original.
Another important reason to save original photos, especially JPG files, is that JPG images use what is called "lossy" compression. To save space on disk, on a memory card, etc., JPG files are compressed, losing some detail in the process. While JPGs saved by a digital camera's "fine" or "ultra fine" mode may seem indistinguishable from RAW lossless images*, if you edit a JPG file and resave the result as a JPG, the file will be compressed again. Every successive save re-compresses the file, reducing more detail and thus the image quality. Sooner rather than later this loss of quality will seem very noticeable.
Before you edit a JPG image file, you should immediately save a copy of the file as a PNG, lossless TIF, or BMP file. This way if you edit the copy, you will be using an image format that does not remove any more data during the save, even though it may compress the file (PNG and TIF) to save space. No matter how many times you resave the file during the editing process, you should not lose detail based on the save itself.
Note that resaving a JPG as a PNG, lossless TIF, or BMP file will only maintain the quality of the original file - it will not replace any detail lost by the original JPG compression.
* RAW images, while most of the time being lossless, also provide other benefits such as being able to change the white balance after the actual photo shoot. However, due to their file size, cameras may take more time to store these images on a memory card, one of several reasons JPG shooting may be desired or even necessary for some photographers.
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