openjpeg is an open-source library for the encoding and decoding of JPEG2000 images.

This page offers some patches which improve its performance slightly.

How much?

I have one solitary test: it is a 1998x1080 pixel image which I am encoding. With the patches described here, on a i3 2.27GHz laptop, an encode of the test image takes 76% of the time that it takes with openjpeg 1.5. The result is bit-for-bit identical.

The patch in one lump

The patch against openjpeg 1.5 is here.

The patch in pieces

I have a repository on github that has the patches split up into steps.