I run windows XP, but the following probably applies to later versions too.

If you turn on Microsoft Cleartype, then they say it adjusts gamma and contrast. It does, you can see it happen. However, what I have not discovered (not bothered to look too much) is how that adjustment is carried out, whether it actually replaces the LUT with a modified version, or sort of has its own LUT before or after the primary one selected. I have found no information as to how this effects any specific monitor calibration software, but one thing is certain, if you have a calibrated monitor, and enable cleartype, then your monitor gamma and contrast appears to change.

I believe this may effect some of situations where folk are seeing differences between print results and monitor screen, since if you have set, for example, srgb icc profile for the screen, what they are seeing on screen will be srgb + cleartype mess up, whereas the printer will be working on the embedded srgb profile only.

Although cleartype does not work for all applications, I suspect that the gamma/contrast adjustment is screen wide, if cleartype is enabled.

Best wishes,

Ray

Hi Terry,

It is designed for anti aliasing of text, but if you read further, it adjusts monitor settings, as I have said - M$ states that and I can see the screen change when you turn it on or off. You can 'tune it', too. Try it and see. The gamma settings effects everything, not just the programs that can use cleartype, afaik. I believe in later os's it is on by default. I believe that it may cause problems with colour settings if it is on and you do the colorimeter thing, since it does not seem to be applied as a normal lut, which could be removed when you calibrate. It will, screw up the screen colours if you calibrate with it off, then turn it on. I'm not sure what happens if it is on, and then you calibrate. In effect, it is like having a double profile, but one of them does not appear in the normal list, afaik.

Best wishes,

Ray

Hi Terry,

It took me some time, searching back through my web history as best I can, and a few emails to someone I know, but I have found the misleading information here -

http://www.microsoft.com/typography/cleartypefaq.mspx

specifically under the Vista settings -


In fact, I've been informed that the last sentence is not true. I had assumed that since microsoft wrote it, and they also provided cleartype, that it was true - silly me.

My windows desktop is plain blue, with lots of icons with white text beneath them. I applied cleartype, and I saw the background colour change - my perception probably being encouraged by the fact that microsoft said that the contrast or gamma values would change. However, now I know that is incorrect, I will try again, with no pre-conceived ideas. I expect it was the effect of the text 'thickening up' on the white edges that gave an optical illusion effect of the gamma changing for the whole screen.

So, for the moment, ignore what I said previously based on what I had read - panic over.

Thanks for prompting me to dig further into this.

Best wishes,

Ray

I was wondering about that too after you brought it up. Tried turning ClearType ON and OFF while watching my desktop. Only thing I saw was the thickening of the type fonts when it was applied - no change in brightness or contrast that I could see. Glad that was cleared up - it was concerning me and how the monitor would calibrate.

Steve W.