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Another pain point on text AA: Many renderers mix up colorspaces on antialiasing. For example freetype assumes a linear colorspace when calculating the antialia

Another pain point on text AA: Many renderers mix up colorspaces on antialiasing. For example freetype assumes a linear colorspace when calculating the antialiased bitmap but AFAIK both GTK and QT apply it directly on sRGB without any adjusting. The result is apparently thickened fonts when displayed black on white and thinned fonts when displayed white on black. Edit: Some background can be read on [0]. [0] https://www.freetype.org/freetype2/docs/text-rendering-general.html#background https://www.freetype.org/freetype2/docs/text-rendering-gener...

enqk 7y ago
I believe it's somewhat unavoidable as the fonts may also have co-evolved to work with renderers that work that way
- leni536 7y ago
  Sure, that's what stem-thickening is meant to compensate in the cited article.
- ahartmetz 7y ago
  Yes - fonts looked too thin and rather ugly when the color space "bug" was fixed in early Qt 5 (on Linux / more precisely, with FreeType glyph rendering) versions. The fix was reverted to fix the look of text.
z3t4 7y ago
With high density monitors on the rise we should get rid of LCD (RGB rainbows) anti alias as its really just a hack.
- leni536 7y ago
  I strongly disagree, also the way the article describes subpixel antialiasing is not entirely accurate. The thing is the boundaries between pixels don't actually exist, it's just a convention so we can address individual pixels and subpixels within them. But these subpixels are not at the same position within the pixels and this needs to be taken into account for antialiasing. Also regarding hiDPI: I know that you just want to get rid of subpixel antialiasing but you really don't want to get rid of antialiasing in general. It's not really an issue with typefaces, but non-antialiased high-frequency patterns can easily generate unwanted Moiré patterns on you display regardless how high is your display resolution.
  - ken 7y ago
    It’s pretty much arbitrary what we as an industry have decided “text” means (and this has changed over the years), and what features it ought to support. It’s largely “what our technology easily supports today”. For example, most people expect antialiasing (i.e., subsampling across space) but we seem to have written off the idea of motion blur (i.e., subsampling across time), except in some games. It’s be technically more accurate to draw a quickly-dragged mouse cursor with a (correctly computed) blur, but that’s not generally easy to render today. And motion blur of moving subpixel antialiased text sounds like a nightmare right now, but with the right abstractions it might not be.
    - leni536 7y ago
      Motion blur is only "accurate" if you assume that the viewer's eyeballs remain still and don't follow the moving object. Having said that not blurring isn't accurate either on current LCDs when the viewer follows the object. This is what black frame insertion is meant to correct.
    - SpaceManiac 7y ago
      Antialiasing (nominally) makes text easier to read. Motion blur makes everything it's applied to harder to see.
  - floatboth 7y ago
    Pretty much no one wants to get rid of antialiasing in general. I use only grayscale antialiasing, even on LoDPI screens. It looks great. Subpixel adds bad color fringes.
    - aibara 7y ago
      Doesn't it depend on the screen and user preference though? On my old Thinkpad's screen grayscale antialiasing looks awful (fuzzier and harder to read), to the point where I've filled bugs when some aspect of a program's UI doesn't obey my system settings.
  - jimbo1qaz 7y ago
- vardump 7y ago
  Addressing subpixels according to their spatial location is no way a hack.
- Const-me 7y ago
  New high-end PCs indeed use high DPI displays, but color LCD monitors are now used in cars, dishwashers and microwaves. These are not high-DPI, and they often lack CPU and GPU power to handle high DPI. Here's a library I've made for an embedded Linux device: https://github.com/Const-me/nanovg https://github.com/Const-me/nanovg At 5" 800x480, subpixel AA improved text a lot.
jjgod 7y ago
Qt does do gamma correction when it comes to text rendering.
- ahartmetz 7y ago
  Maybe for blending, white on black text and things like that - after calculating shades the "wrong" way for compatibility with fonts' built-in expectations. See my other comment about that.

enqk 7y ago

I believe it's somewhat unavoidable as the fonts may also have co-evolved to work with renderers that work that way

leni536 7y ago
Sure, that's what stem-thickening is meant to compensate in the cited article.
ahartmetz 7y ago
Yes - fonts looked too thin and rather ugly when the color space "bug" was fixed in early Qt 5 (on Linux / more precisely, with FreeType glyph rendering) versions. The fix was reverted to fix the look of text.

z3t4 7y ago

With high density monitors on the rise we should get rid of LCD (RGB rainbows) anti alias as its really just a hack.

leni536 7y ago
I strongly disagree, also the way the article describes subpixel antialiasing is not entirely accurate. The thing is the boundaries between pixels don't actually exist, it's just a convention so we can address individual pixels and subpixels within them. But these subpixels are not at the same position within the pixels and this needs to be taken into account for antialiasing. Also regarding hiDPI: I know that you just want to get rid of subpixel antialiasing but you really don't want to get rid of antialiasing in general. It's not really an issue with typefaces, but non-antialiased high-frequency patterns can easily generate unwanted Moiré patterns on you display regardless how high is your display resolution.
- ken 7y ago
  It’s pretty much arbitrary what we as an industry have decided “text” means (and this has changed over the years), and what features it ought to support. It’s largely “what our technology easily supports today”. For example, most people expect antialiasing (i.e., subsampling across space) but we seem to have written off the idea of motion blur (i.e., subsampling across time), except in some games. It’s be technically more accurate to draw a quickly-dragged mouse cursor with a (correctly computed) blur, but that’s not generally easy to render today. And motion blur of moving subpixel antialiased text sounds like a nightmare right now, but with the right abstractions it might not be.
  - leni536 7y ago
    Motion blur is only "accurate" if you assume that the viewer's eyeballs remain still and don't follow the moving object. Having said that not blurring isn't accurate either on current LCDs when the viewer follows the object. This is what black frame insertion is meant to correct.
  - SpaceManiac 7y ago
    Antialiasing (nominally) makes text easier to read. Motion blur makes everything it's applied to harder to see.
- floatboth 7y ago
  Pretty much no one wants to get rid of antialiasing in general. I use only grayscale antialiasing, even on LoDPI screens. It looks great. Subpixel adds bad color fringes.
  - aibara 7y ago
    Doesn't it depend on the screen and user preference though? On my old Thinkpad's screen grayscale antialiasing looks awful (fuzzier and harder to read), to the point where I've filled bugs when some aspect of a program's UI doesn't obey my system settings.
- jimbo1qaz 7y ago
vardump 7y ago
Addressing subpixels according to their spatial location is no way a hack.
Const-me 7y ago
New high-end PCs indeed use high DPI displays, but color LCD monitors are now used in cars, dishwashers and microwaves. These are not high-DPI, and they often lack CPU and GPU power to handle high DPI. Here's a library I've made for an embedded Linux device: https://github.com/Const-me/nanovg https://github.com/Const-me/nanovg At 5" 800x480, subpixel AA improved text a lot.

jjgod 7y ago

Qt does do gamma correction when it comes to text rendering.

ahartmetz 7y ago
Maybe for blending, white on black text and things like that - after calculating shades the "wrong" way for compatibility with fonts' built-in expectations. See my other comment about that.