sub-pixel smoothing on retina: a bug?

[stewacide]

Recently acquired a 13" rMBP. I notice now that it defaults to using sub-pixel anti-aliasing when in "best for retina" mode, which seems excessive/pointless but does no harm (although I think text looks better with it turned off: sharper anyway). But I notice that it ALSO defaults to employing sub-pixel antialiasing when in supersampling scaled mode, which of course breaks the effect completely and results in blurry mis-formed 'fringed' text (you've just never noticed it because the resolution is so high).

IMO this is definitely a bug Apple should fix (if they haven't in the 10.8.3 betas?), probably by disabling the capability completely on Retina Macs (and at least removing it as the default). I'd advise to turn "Use LCD font smoothing when available" off in the General preference pane, especially if you run at non-Best for Retina resolution.

There may also be a performance advantage to this (I assume there's some overhead to doing sub-pixel anti-aliasing over pixel-level anti-aliasing). There's also an image quality improvement when zooming in/out text (e.g. in Mission Control, zooming pages in Safari and using Safari's view-all-tabs mode, etc. as there's no colour fringing)

 

[Ultra AleM]

It is not good looking because the scaled resolutions are not proportional.

The "Best for Retina" is 2x pixels, so everything is just doubled and mantains the ratio. The other ones are not.

 

[leman]

I completely agree. Furthermore, I believe that the biggest drawback of the Apple's (otherwise ingenious) supersampling implementation is that its impossible to do pixel-perfect rendering anymore, as the backing store pixel do not necessarily align to the physical pixels. Of course, one may ask whether pixel-perfect rendering is an outdated hack with the HiDPI displays, but I believe there are still practical usage cases. For instance, 'true' photo/video display independent of current resolution (so that the 1080p video maps to the physical pixels no matter the backing store settings, bypassing any scaling), that could be very useful for photo professionals. AFAIK, currently there is no way to pull this off in Cocoa (correct me if I am wrong).

 

[stewacide]

Two blown-up screengrabs. Both in virtual 1440x900 mode on a 13" Retina Macbook (i.e. both are rendered at 2880x1800 and downscaled to native 2560x1600. The top is with LCD smoothing on, the bottom with it off. While that colour fringing is normal and correct when rendered at native resolution (see: http://en.wikipedia.org/wiki/Subpixel_rendering), here it's obviously wrong, as shown clearly by the " character. Both apostrophe (') marks are identical and should be rendered identically, whether using sub-pixel anti-aliasing or not, but in the top shot they're different because it isn't sub-pixel smoothing you're seeing, just incorrect blurry fringing artifacts.

I don't think there's any way Apple could correctly implement sub-pixel AA on scaled resolutions even if they wanted to (which would be pointless IMO), given how they've chosen to do arbitrary scaling in OSX. They just need to remove it completely for HiDPI displays.

 

[leman]

It is not good looking because the scaled resolutions are not proportional.

The "Best for Retina" is 2x pixels, so everything is just doubled and mantains the ratio. The other ones are not.

I have no idea what you mean by this. The ratio is maintained no matter what resolution you select. And all available resolutions on the rMBP have the same ratio - 16:10

P.S. Its also not correct that everything is doubled. Only image data gets doubled, everything else is rendered at 4x resolution.

 

[stewacide]

...down-sampling traditionally smoothed text is also less than ideal (would be neat to see how it'd look with no anti-aliasing at all, but I don't know how to turn it off completely in OSX), but down-scaling sub-pixel anti-aliasing is just blatantly stupid. I'm surprised nobody in Apple's typography department has brought this up to the OS team yet.

 

[yakovlev]

You should file a bug report at https://bugreport.apple.com.