JPEGhack

Revision as of 19:05, 24 June 2011

Once upon a time, I was thinking about lossless jpeg editing. The sort that jpegtran can do.

jpegtran (1)         - lossless transformation of JPEG files

Specifically, jpegtran can (within limits) rotate/flip/mirror losslessly, and also crop - for values of "lossless" that only apply to the cropped image data.

And I wondered if the reverse could be true. If jpeg image data can be cropped losslessly, then it cannot rely on surrounding data. Thus surely paste is equally possible.

I researched, and found... http://www.imagemagick.org/Usage/formats/#jpg_lossless. Scroll down to the 'Mixed JPEG Quality' section where it's suggested

* use jpegtran to merge the q60 on top of the q100

So, jpegtran can do that, huh?

nope.

But an experimental version can. http://jpegclub.org/jpegtran/

That reads to me that the 'drop' option has been experimental since 2000 at least... but, let's take a look. There are helpful binaries and a sample script provided, but I had something a bit more fun in mind.

One download later, and some fiddling around... and here is this!