Mike Chaney's Tech Corner

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

Ray,
As far as I can see from the MS information, Clear Type is merely Anti Aliasing on text, no more, no less.
http://www.microsoft.com/typography/WhatIsClearType.mspx
Terry.

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

I have read further and all I can see is this;
And all this is in the context of text and a description of anti-aliasing.

The other point is, I can mess about with the clear type settings and do not see any changes on screen other than with text, checked within Qimage therefore colour managed.
Just leave it on all the time if you are seeing differences.
I'm sure this would have come up long ago if clear type did really affect your calibration. Next time I calibrate and do a validation check, I'll try the check with clear type on and off. That should, I think, be reflected in the dE2000 errors.
Terry.

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

Glad to hear it, no worries  ;)
Terry.

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.

Hi Steve, everyone,

Sorry if it got you bothered. I have 216 folders and icons on my desktop, so the white text is a big proportion of the background. Afaik, the contrast adjustment is applied to the anti-aliasing pixels added to the edges of the characters, not to the whole screen. However, I've yet to test that out. I shall screen off the area where the icons are -most of the vdu - and carefully watch the remaining patch of blue as I turn cleartype on and off. I'll report back what I find here, for the sake of completeness.

Best wishes,

Ray

Update - It was an optical illusion for me. fwiw, I've left cleartype turned off.