The quality of a JPEG image file (.jpg) may be substantially degraded by JPEG compression, especially if the file is saved repeatedly, since it is re-compressed each time it is saved.

A JPEG file is encoded using an adjustable "lossy" compression algorithm. Lossy compression methods reduce the filesize of images by removing and throwing away data that is considered relatively inessential to the integrity of the image.

As a greater degree of JPEG compression is applied to an image, the size of the image file becomes smaller. There is, however, and inherent tradeoff between image filesize and image quality. At relatively low compression ratios, JPEG compression can be very effective and efficient. Selecting a relatively high compression ratio, though, will result in files that are very small in size, at the expense of a substantial reduction in image quality, including the introduction of undesirable artifacts and other "noise" in the image.

Since the lossy JPEG compression method removes and discards image data, once an image has been compressed (or over-compressed), the effect is permanent. There is no way to "repair" an overly-compressed JPEG image. Converting the image to TIFF or any other format does nothing to restore the image data removed by the JPEG compression.

The best defense against the possibility of JPEG image quality loss is to always edit and save a copy of the image. Retain the original image so that you may easily revert to it, in case too much compression overly-degrades the working copy of it.

^{- jb/wa}