XnView Software

if i have a jpg from my canon 5d, and i crop it and do a save-as
to a new file, does the image get recompressed?

how about if i resize it?

are there ways to avoid recompressing data in these scenarios?

thanks,
BabaG

There's a short answer...

Olivier_G ([url=http://newsgroup.xnview.com/viewtopic.php?t=8069]Jpg compression after crop[/url]) wrote:Another idea to try: make a copy of the JPEG file, open it in XnView, make your selection and try from Menu: Tool>JPEG Lossless transformations>Crop.
It will crop the picture without any JPEG recompression (no loss of quality), directly in the file, although it does it with a 8x8 pixels accuracy only. I don't find this very straightforward, but it may be interesting in your situation.
Remember: try on a copy of your JPEG, as this "JPEG Crop" is applied & saved instantly without any confirmation.

... and a long one

Any time you save a JPG, if either the image data or the compression settings have changed at all, it will get recompressed. The only exceptions to this are the JPG lossless transformations (which are risky because they are applied directly to the image immediately, and in cases like cropping, can't be undone). You can minimize the ammount of additional data loss caused in the recompression by going into the options for saving JPGs and set the quality level extremely high & choose the "use estimated quality" setting, but you will still wind up with some additional loss. On the other hand, it's probably not something you need to worry about. Unless you use very high compression each time, it usually takes many recompressions before you'll notice visible quality loss.
What you should do is take an image, save a copy of it, then repeatedly recompress that copy until you can see an unacceptable quality loss. This will show you your threshold, and let you know how many times you can get away with recompressing a given image.

thanks for the info folks. how does the lossless jpeg apply to nconvert?
i suppose for safety's sake one would make a copy and apply lossless
crop to the copy. does that make sense. reason i ask about this is i have
projection images. while most recompression wouldn't be perceptible in
a print, i worry that projected at very large sizes recompression
artifacts may become more visible.

thanks again,
BabaG