Flutterby™! : Hacking JPEG

Next unread comment / Catchup all unread comments User Account Info | Logout | XML/Pilot/etc versions | Long version (with comments) | Weblog archives | Site Map | | Browse Topics

Hacking JPEG

2011-02-07 18:14:55.049317+00 by Dan Lyke 1 comments

Oooh! Cool idea! JPEG canaries: exposing on-the-fly recompression.

Our algorithm works by adding a high-frequency pattern to the image with an amplitude carefully selected to cause maximum quantization error on recompression at a chosen target JPEG quality factor. The amplitude is modulated with a covert warning message, so that foreground message blocks experience maximum quantization error in the opposite direction to background message blocks. While the message is invisible in the marked original image, it becomes visible due to clipping in a recompressed copy.

What's also cool is how their sample images look as you scale 'em on the iPad.

Hat tip to MarkV.

comments in ascending chronological order (reverse):

#Comment Re: made: 2011-02-08 12:34:16.244948+00 by: DaveP

Spiffy! I had figured such a thing was possible, but had never figured out the math to make it happen.