Scott T: The Blog

Beating JPEG

Posted Wed, Jul 01, 2009 at 11:03pm by Scott
Tagged: games, programming, scummvm

One of the main sticking points for working on The 11th Hour recently (ignoring lack of time) has been the still frames within ROQ files. Although seemingly trivial within T7G, 11H uses more complex/advanced image compression for both video and stills. The video frames have been working for a while with some very minor glitches however the still frames use JPEG, and it's hard to find a decent documentation source. Never-the-less, some work had been done prior to now by clone2727 (for Mohawk) and jvprat which I obtained last week and then became rather obsessed with fixing =P

From rather simple beginnings, there were some rather critical issues to be fixed first (ie, missing functionality) which rapidly pushed towards a greyscale image.

Fiddling here and there resulted in a vast number of -ish improvements until a breakthrough resulted in the following:

All the AC components of the image seemed fine so after fixing an issue with the DC values, success was reached. Five minutes of tinkering to add JPEG to the 16bpp branch and we have the final image, rendered in RGB.

For those interested in the progress shots, the (semi-permanent) gallery has many ways of not to decode a JPEG.


Excellent work! You kept that one quiet ;-) Can't wait to try it when I get home!

Posted Thu, Jul 02, 2009 at 2:39am by spookypeanut

Well, I've been looking through the specs for the last month but I only really started serious fiddling a last week. I would have shared my progress but you haven't been on IRC recently a whole lot =P

Posted Thu, Jul 02, 2009 at 4:25pm by Scott

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