Saving a lossless JPEG

by cday (Posted Wed Mar 09, 2016 10:53 pm)

kliefoth wrote:I have a few JPEGs, 30-50MB each, that want to make alterations to, then save without losing too much data. Each time I save them after making minimal alterations (color, levels, no cropping), the file goes from very large to about 20-30% of its original size in MBs. Why is that? If the file is close the same quality as the original (these are hi-res film scans), shouldn't the size be approximately the same? They even seem to fail the eye test, though that's subject to doubt.

JPEG is a lossy file format but for photographic images which generally have continuous tones, as opposed to for example scans of text which has sharp edges, it is often possible to obtain a substantial reduction in file size with little or no perceptible loss of quality, although there is a limit, of course.

If you are opening the images in XnView Classic and then saving them, the compression used is set in the dialog displayed when the Options button in the save dialog is clicked:



There is quite a lot of information available online and from searching the forum on understanding and using the JPEG file format.

kliefoth wrote:I'm happy to save as a another type of file, but after trying a couple (JPEG 2000; RAW), they wouldn't open again after I saved them. Help!

That's a different question, but if you research JPEG compression a bit you will likely find that, suitable applied, it will meet your needs!

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