Doctor M is on the right lines, but has slightly misremembered the facts:

Doctor M said:

IIRC, the problem with DVD calibrations such as the THX Optimode is the method involved.

The Optimode calibration video/audio is intended to go through the same processing as the movie itself.

This is correct. Modern video card drivers have separate settings for the desktop and the video overlay. So if you use the THX Optimizer, DVE, etc. to set up your monitor for DVD playback in a media player, then look at a JPG on the internet, your monitor may give you different set of levels.

I would recommend you rip the calibration screens off the DVD and save them as BMPs. Also be careful because some MPEG-2 decoders don't give you accurate colours, ie avoid VirtualDubMod and use DGIndex or the latest VirtualDub w/MPEG-2 decoder plugin instead.

Once your monitor is calibrated for your desktop, leave the monitor settings as they are, then calibrate DVD playback by adjusting the video overlay settings in your graphics card drivers.

As a result the Optimode for a given DVD is so you can calibrate your home theater so it is accurate for that DVD only. It is not an absolute calibration for accuracy.

(At least this is what I remember reading way back when. I hope they've changed that.)

This is incorrect. The THX optimizer screens on the Star Wars discs are the same as the Indy discs, etc. (I've checked!)