DropMedia Flip & Rotate - 1.1

OK, I got off my lazy butt and tried out this app. The bottom line is, it does not do lossless conversions.

I took an image straight out of my 3 MP camera, with 1:19 JPEG compression ratio. Original file size: 640 KB. First I used GraphicConverter to rotate it 90. New file size: 636 KB. Still 1:19 ratio. Then I used this app to rotate it 90. New file size: 2.8 MB; 1:4 ratio. So it is clear to me that the image file was read in, uncompressed, rotated, then recompressed (albeit at a very high quality) and then written back out. There are 2 problems with this approach:

1. Despite your best efforts, any amount of compression will result in a generational loss of quality. This is an unavoidable fact. It's just the way lossy compression schemes like JPEG work. This generational loss could be avoided by either offering true lossless transformations, or by using a lossless format such as TIFF for saving the postprocessed images.
2. If the loss in quality is to be minimized, then the resulting file must end up being significantly larger than the original file. This is the approach currently taken by this app. The alternative is to output an image file that is roughly the same size as the original, but heavier compression is needed in such a case, which further degrades image quality. The point of this is that your image file size can increase by 4x (or more?) when using this app! Do that on a folder of 200 photos, and, wow, that's a huge amount of disk space you just ate up.

The solution: a command-line tool called jpegtran.

jpegtran simply manipulates the EXIF header to achieve the desired transformation. All the "real" image data is left untouched. Here are links to more info about jpegtran:

• a list of many many apps (mostly for windoze) that use jpegtran to do truly lossless transformations
• Independent JPEG Group -- the developers of jpegtran
• Google results for "jpegtran man" -- interesting reading

I hope this info helps...

Just a tip for anyone who cares....

I'll stick with Graphic Converter for rotation of my JPEG images. I haven't researched the subject to death, but there are only a few apps out there for the Mac that do lossless image rotation & mirroring. This is important because most tools that rotate/mirror your images will read in the JPEG, uncompress it, rotate, then recompress when saving to disk. Voila, 1 completely unnecessary generation of degradation. You have just lost information that can not be regained once you trash the original source file.