On 13 Jan 2014 17:13, "Dave Arnold" <
address@hidden> wrote:
Hi Mike,
I have reproduced your results with version 0.0.15 of Cantarell-Regular (CFF). I do not see any FreeType bugs, but have found some system integration and font issues. Here is what I have found.
1) The new CFF rasterizer automatically increases the weight of fonts at small sizes, in order to maintain contrast and improve readability. To do this, it assumes the system is adjusting gamma for text (as Werner mentioned earlier). In most displays, I find a compromise of gamma 1.8 is best, but anything down to 1.4 should look ok. Your screen shot shows that that linearized blending is not being used on the text. That is, gamma adjustment is not being done, and your gamma is 1.0. Using gamma 1.0 has several negative effects on anti-aliasing; one is to make black-on-white text look heavier. So, we are effectively darkening the text twice. I don't know if this is a Fedora issue or a LibreOffice issue. FreeType does have a control to disable darkening, and that might help work around the issue if you can't get the system to do gamma adjustment.
2) The hints in Cantarell-Regular are wrong for many glyphs. In CFF fonts, the hints describe where the important stems of the glyph are located. The rasterizer then works to align those hints to the pixel grid. Normally, this would align the stems as well. In Cantarell, the hints don't always match the stems. For example, the top of the 'c' has a hint at (408,481) while the stem is actually at (423,491). On the other hand, for the 'o', which has a very similar shape, both hint and stem are (426,490). As a result, the 'c' shows overshoot while the 'o' does not. This overshoot contributes to a general fuzziness apparent on most lowercase letters.
I have attached a screen shot comparing the rendering you are seeing with our expected rendering. This was prepared using FreeType's ftview program, 15 ppem Cantarell v0.0.15 and gamma 1.8. It addresses issue 1). Issue 2) is improved because the overshoot is lighter.
Please let me know if you have any questions. Thanks.
-Dave
On 1/13/2014 11:52 AM, Michael Cronenworth wrote:
Dave Arnold wrote:
Thanks for sending the screen shots. It gives me a better idea of what you are
seeing.
Are you finding any problems with Nimbus Sans or Sans, or just with Cantarell?
Cantarell is the only font that I have seen have negative effects. As shown in
the screenshots, other fonts appear normal, as do Monospace type fonts in terminals.
As Werner says, we expect rendering differences in CFF fonts for 2.5.0, so I
assume you are using a CFF version of Cantarell. I agree it is surprising how
much darker the 2.5.0 rendering of Cantarell is in your screen shot. Also, it is
showing overshoot at baseline and x-height. That would contribute to fuzziness.
I'd like to understand this better, but I have not been able to locate an
OpenType/CFF version of Cantarell; I can find only OpenType/TrueType versions.
Could you send me a copy of the font you are using for your test?
Fedora uses the font directly from upstream with no patches/features applied.
http://ftp.gnome.org/pub/GNOME/sources/cantarell-fonts/0.0/cantarell-fonts-0.0.15.tar.xz
Running "fc-query" on the file reports "fontformat: "CFF"(s)" so I assume the
latest upstream font generates an OpenType/CFF version, but I am not a font expert.
You can find the Fedora package on the Fedora build system. If you do not have a
system to extract the otf files I could place them somewhere.
http://koji.fedoraproject.org/koji/buildinfo?buildID=467138
Thanks.
Thank you for looking into this. There are many user reports of this issue so
my, subjective, opinion that the Cantarell font looks "worse" is not unique.
https://bugzilla.redhat.com/show_bug.cgi?id=995643
https://bugzilla.redhat.com/show_bug.cgi?id=1035486
https://bugzilla.redhat.com/show_bug.cgi?id=1051689
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