Some french fellows mailed me that xcalib doesnt work with high-end video cards which use >8bit LUTs. Okay, I had to add interpolation.
Before this happened bleader and gl.tter sent me patches for multi-monitor support. Now ATI FGLRX users and Windows users should benefit from these patches and be able to set the LUTs per display (if the hardware supports this).
This resulted in a new xcalib version that you can download from