The FXScript Reference

There is a bug in ImageXor which will do something to corrupt the first source image passed to it. I've found it will taint the whole image buffer even affecting processes later on. The effect is unpredictable color, either on the desktop preview or the video monitor. This can sometimes look like a RGB in YUV color error, but doesn't seem to be correctable with PixelFormat functions.

A workaround I've found is to duplicate the intended source into a secondary image buffer and use that for the source. The wierdest addition to this workaround is that the temporary source buffer needs to be reset again after the ImageXor function. The following was working for me in FCP3.02 when I wrote this:

dest = src1;
    imagexor(dest, xbuffer, xbuffer2);
    dest = src1;

The second assignment of src1 into dest is essential to prevent the corruption from popping up when dest is used again later in the script.

There is (was?) a related bug with Blit where the source polygon would be altered by the function.