JPG Image Sizes

[milest]

Transferred some hi-quality jpg files from my camera to my PC and then worked them in Adobe PS2, merely cropping them and resaving them (at the highest PS2 quality setting). Was surprised that the newly saved files were twice the size of the originals (2MB vs 1MB). Why so?

[chuckmoser]

Probably because the jpeg compression level was set lower when saving from Photoshop than the jpegs from the camera.

[another view]

I'm not sure I've got the answer but I'll make a guess at it. I think cropping has something to do with it. Here's why:

The amount of jpeg compression is set by the camera (and re-saving in photoshop). How big the file size has to do with this and also what's in the shot. If you shot a clear blue sky, and also a shot with a lot of detail to it, the shot of the sky would be a smaller file assuming both shot with the same settings on the camera (fine mode, etc). What happens is that there's a lot of redundant information in the sky shot (lots of the same color blue) so a lot more information can be discarded but still "read" correctly when viewing the image. A shot with more detail will have less redundant information, so less information can be discarded - more information equals larger file size.

Now by cropping the shot, if you cropped out areas that didn't have much detail (as in the sky above your subject) then overall the shot would have more detail to it. But this is assuming that you interpolated it back to the native file size (like 3024x2016 pixels or whatever).

Again, just a guess...