| The question of what happens with metadata probably depends on the software.
Programs that focus on metadata / cataloging are less likely to mess with the actual image data than those that are predominantly pixel editors.
I know that a program like Exiftools works because it doesn't touch the image data. That allows it to access Exif, IPTC, etc in as many formats as possible since those headers are in roughly the same format in all file formats (with the caveat that maker notes will vary).
Of course, if you are legitimately concerned with file degredation, why not test a file out for various situations. For instance, repeatedly change the metadata on a copy of a file. Compare the repeatedly tested file with the original. You could even use Photoshop to subtract the modified image from the original in two layers so that the differences become obvious (if there are any).
You could also test an image in photoshop by repeatedly saving it (i.e. purposely recompressing the jpg file). See how that differs from the original.
The one thing I'd wonder is what Lightroom might do. While it specializes in cataloging, it is also the type of program that might take the easy way out and just completely resave an image thus causing degradation. I haven't worked with it enough or know enough about it to know what it might do.
My own choice of cataloging software, IMatch, doesn't access the pixel data when it edits metadata according to the author, and I haven't found reason to doubt it... I have repeatedly changed some metadata on early jpgs as I learned to use that particular program, and I've never noticed any differences.
It will be interesting if anyone does do a test of some of the more mainstream programs and what happens when you either change metadata or even just continually save a jpg that is changing pixels.... i.e. how fast does image degradation occur, if it occurs given that nothing else really changes. I imagine that once you actually start editing pixels be it curves, sharpening, etc that degradation will go a lot faster in those cases. |