Why Windows fonts have coloured antialiasing?

[Guillermo Luijk]

This is something I wondered many times: when you use fonts in Windows applications (such as MS Paint) with AA applied, blue and magenta casts appear on the edges even if pure black colour is chosen for the text. See here compared to 100% black fonts in Photoshop:




Does anyone know the reason for this? may it increase performance to render these texts more quickly in the OS?. I cannot imagine why this could mean any advantage in terms of image quality, after all B&W text is what we wanted. Is this kind of AA perceptually more pleasant?.

Regards

[hjulenissen]

https://en.wikipedia.org/wiki/Subpixel_rendering

They are exploiting the distributed nature of r/g/b subpixels on your display to push the limits for luminance resolution, much like how demosaicing algorithms tries to dig out luminance information from every CFA filtered sensel on your camera.

When Windows used to have a "font preference tuner", it seems that they used our sight to determine if the display was r-g-b type or b-g-r type, and if the gamma was way off.

It seems that this trick has gone out of fashion with recent Windows releases. Perhaps because we have retina displays now, perhaps because hand-held devices can be rotated 90 degrees.

-h

[Guillermo Luijk]

Very interesting, thanks! nice to see Windows was going a step beyond. I just need now Cortana listening to me when I raise a prayer to her

Regards

[biker]

In Windows 10 it's definitely still present. On a 24" screen @1920x1080 it's pretty annoying from distances shorter than 1m (3.3ft.) The coloured edges are clearly visible.
It's a help for hi-res (4K) displays or small devices though - making texts look really smooth.

[Simon Garrett]

I just need now Cortana listening to me when I raise a prayer to her

Regards

Careful!  Everything you say to Cortana, Microsoft's Satya Nadella gets a copy. 

[Peano]

It's chromatic aberration, same thing that's happening in the attached. WHY it happens in the windows applications I do not know, but that is WHAT is happening.

[TonyW]

It isn't CA as that is associated with lenses.  The answer was given earlier by -h as sub pixel sampling.
http://annystudio.com/misc/anti-aliased-fonts-hurt/

Strangely enough I just had a look in Win 10 and cannot see it.  What font are you using where you see the effect?

[Bart_van_der_Wolf]

It isn't CA as that is associated with lenses.  The answer was given earlier by -h as sub pixel sampling.
http://annystudio.com/misc/anti-aliased-fonts-hurt/

Strangely enough I just had a look in Win 10 and cannot see it.  What font are you using where you see the effect?

Hi Tony,

I don't know about Windows 10 (I've yet to upgrade), but on Windows 7 you need to turn on 'ClearType', and calibrate it for your particular display. Maybe searching for "ClearType" will give you something similar to the attached Win7 dialog, if that technology is still used in Win10.

Cheers,
Bart

P.S. A side-effect of this technology is that screen captures of text (like my attachment), may not look as good on all displays, depending on the specific R/G/B LED layout of one's display. It gets to be less of an issue if screen resolution approaches 300 PPI, but it does help apparent sharpness of anti-aliased text on lower resolution displays.

[TonyW]

Hi Tony,

I don't know about Windows 10 (I've yet to upgrade), but on Windows 7 you need to turn on 'ClearType', and calibrate it for your particular display. Maybe searching for "ClearType" will give you something similar to the attached Win7 dialog, if that technology is still used in Win10.

Cheers,
Bart

P.S. A side-effect of this technology is that screen captures of text (like my attachment), may not look as good on all displays, depending on the specific R/G/B LED layout of one's display. It get's to be less of an issue if screen resolution approaches 300 PPI, but it does help apparent sharpness of anti-aliased text on lower resolution displays.

Thanks Bart,
The reason I could not see it in Paint was due to viewing at 100%.  Increasing to 400% the coloured anti aliasing evident.  Photoshop handles this much better IMO showing grey shades rather than colour.  I think that it may be better or worse depending on choice of font family.

Adjust Clear Type Text is still part of Windows 10

[Bart_van_der_Wolf]

Here is some more technical background info about this Sub-pixel Font rendering, by Steve Gibson, from the early days of such attempts to improve anti-aliased font rendering resolution.

Cheers,
Bart

[hjulenissen]

The Gibson link is a great resource, Bart.

This post has a nice summary of Windows vs Mac font rendering philosophy (at the time):
http://www.joelonsoftware.com/items/2007/06/12.html

https://www.smashingmagazine.com/2012/04/a-closer-look-at-font-rendering/

http://alienryderflex.com/sub_pixel/

-h

[Guillermo Luijk]

The last link is greatly illustrative, including microscope pictures of the RGB array on LCD screens. The conclusion is that the final horizontal resolution improvement achieved could doubtfully be worth the effort, but the technique is very smart and interesting.

Regards!

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[razrblck]

As for why Photoshop does it differently, its implementation is more general purpose as it should look good both on electronic and physical media. Windows can get away with RGB anti aliasing because it only has (had?) to display on screens.

[Bart_van_der_Wolf]

As for why Photoshop does it differently, its implementation is more general purpose as it should look good both on electronic and physical media. Windows can get away with RGB anti aliasing because it only has (had?) to display on screens.

Yes, and since it requires an Operating System's support, there is little benefit for Photoshop to change the Font rendering mechanism, and it wouldn't know the order of the RGB lines, or other arrangement pattern (that's why it needs to be calibrated on the display one uses). Traditionally, Photoshop was used more for Pre-Press activities, and that would mean that Type is set at very high resolutions, where traditional anti-aliasing is enough if not already overkill.

Display resolutions were traditionally very low (1/4th or 1/3rd of visual acuity at reading distance), so they can/could use all the help they can/could get. But even with high resolution displays, there may be some benefit (still sharper and less stressful to read) for rendering very small fonts.

Cheers,
Bart

[Guillermo Luijk]

Hey! I have just realized my first picture shows an AA colour pattern that should work on a BGR LCD display rather than a RGB, since reddish AA is on the left and bluish to the right of the edges:



Later I configured Clear Type (Windows 10 allows for Callibrating through several 'choose the text you can read best' steps) but I cannot check now if the AA colour pattern has changed. I am not even sure if fonts were rendered more sharply after this configuration step. I have a Toshiba laptop.

CORRECTION: Ok my sample was black font over white background, so the pattern is correct. The opposite to:



Regards

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[biker]

There also is a SubLCD routine allowing you to do the same with pictures/photographs.
This way you can have for example a doubled resolution wallpaper on your screen if you don't mind possible slight edge colouring. But you must ensure displaying exactly 1:1 (picture pixel:scren pixel).