hendrikm opened this issue on Dec 31, 2002 ยท 24 posts
Misha883 posted Tue, 31 December 2002 at 2:30 PM
Attached Link: http://jpegclub.org/losslessapps.html
Such interesting questions on this forum! [And excuses for me not to fold the laundry...] I did a little research, and found this (unsubstantiated) quote: "There are a few specialized operations that can be done on a JPEG file without decompressing it, and thus without incurring the generational loss that you'd normally get from loading and re-saving the image in a regular image editor. In particular it is possible to do 90-degree rotations and flips losslessly, if the image dimensions are a multiple of the file's block size (typically 16x16, 16x8, or 8x8 pixels for color JPEGs). This fact used to be just an academic curiosity, but it has assumed practical importance recently because many users of digital cameras would like to be able to rotate their images from landscape to portrait format without incurring loss --- and practically all digicams that produce JPEG files produce images of the right dimensions for these operations to work. So software that can do lossless JPEG transforms has started to pop up. Bu tyou do need special software; rotating the image in a regular image editor won't be lossless." The link goes to a bunch of applications designed to do the rotation. But, (assuming Minolta knew what they were doing), Michelle's method should also work, as the rotation in the camera *should* be lossless. So, the next thing enquiring minds wanted to know, does Photoshop (v7) handle JPEG rotation correctly? I ran some experiments below: