Red Hat Bugzilla – Bug 857860
ligatures in Calibri appear bold
Last modified: 2013-08-01 01:09:33 EDT
Created attachment 613610 [details]
Description of problem:
With Calibri (11pt) ligatures are very noticeably visually different to surrounding text. They stand out as if bolded.
Version-Release number of selected component (if applicable):
rpm -q freetype fontconfig
Steps to Reproduce:
1. Install Calibri
2. Set font of gedit to Calibri 11pt
3. Type "anti off often little"
I suppose this is using the autohinter? I would be surprised if that's the case in fact, but that's the only way to explain the bug.
This is not a bug. The calibri font contains some bitmap strokes for small sizes (among them for 15ppem, which is your 11pt at 96dpi). However, they are incomplete and cover only the latin1 glyph set. Ligatures like `fi' or `ti' are not covered. Additionally, the glyphs from the bitmap strokes are noticeably thinner.
If you want a consistent appearance, you have to disable bitmap strokes.
Ah, so it's a font bug. I wonder what the rendering on Windows looks like then...
FWIW, we have had observed this same behavior with other, older, Microsoft fonts also. We should assess completely disabling bitmaps by default.
Created attachment 613895 [details]
Screenshot from Windows
Just out of interest, here is the rendering of Calibri in Firefox 3.6 on Windows XP with no font smoothing or ClearType. Somehow, it is getting consistent stroke widths.
Indeed, this is strange. I have 5.62, and its `gasp' table says to do anti-aliasing even in the range 9<ppem<=19. However, your image clearly shows that the font gets rendered in B/W mode, which is the only choice to get consistent results if you mix hinted glyphs with embedded bitmaps. So the gasp table of my version is incorrect, it seems.
What version of Calibri are you using? I can ask someone at Microsoft for clarification.
I have two versions of Calibri locally to test with, 1.02 and 5.62, but I get the same results with both.
Created attachment 613978 [details]
Windows "Standard" font smoothing
Calibri version 5.62 on Windows XP with "Standard" font smoothing. Seems that the bitmap strikes aren't used at all?
Created attachment 613979 [details]
Windows "ClearType" font smoothing
Calibri 5.62 on Windows XP with ClearType.
Ok, so what I think we need is to make FreeType / Fontconfig / Cairo etc implement these rules:
- Since bitmaps are binary images, only use embedded bitmaps if antialiasing is off.
- Respect gasp tables.
I like to see both be implemented at the FreeType's 'default' level, instead of apps having to worry about these.
Now, these may not fix this bug per se, but both sound like a step in the right direction.
Hmm. FreeType is completely unaware of `gasp'. Especially with the introduction of ClearType, handling of `gasp' has become non-trivial. I would really like to not add this.
To be more specific, handling of `gasp' belongs into the same category as handling OpenType tables, this is, one level higher.
Greg Hitchcock replied as follows:
The simple answer is that the gasp table was designed for and only applies when font smoothing is enabled.
The intention of the gasp table was to fine-tune the grayscale work. The Calibri font was initially only designed and hinted for ClearType, the gasp table settings and the sbit data was intended to *help* Calibri work better with either bi-level text or font smoothing.
(In reply to comment #11)
> Hmm. FreeType is completely unaware of `gasp'. Especially with the
> introduction of ClearType, handling of `gasp' has become non-trivial. I
> would really like to not add this.
This is where we disagree :). If it's non-trivial, it's even more non-trivial for FreeType-using pieces of the stack...
(In reply to comment #12)
> To be more specific, handling of `gasp' belongs into the same category as
> handling OpenType tables, this is, one level higher.
I wouldn't think so. It directly affects rasterization, and as we have established in other threads, rasterizing using bytecode hinting with disregard to gasp table can be problematic. Sure, we can force all FreeType users to implement gasp table handling, but I see it more fit in the library itself.
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