[ft] Accuracy of generated glyphs in smaller bitmaps

[Jordan Lehmiller]

Hi All,

 

We are having an issue with one of our TTF fonts, where the generated bitmaps look radically different between smaller and medium resolutions. 

 

I attached a screenshot of some bitmaps Freetype generates from our Assuan TTF font at 26x26, 36x36, and 52x52 (values plugged into FT_Set_Pixel_Sizes).  The bitmaps generated at 36x36 and above are acceptable, but at 26x26 and below, the font looks pretty bad (Note the 'RE' combination in the image).  It is very important for us to keep all font sizes below 32x32 since we have very limited amounts of memory to work with.  Also since some of the aesthetic detail is lost when generating the glyphs, the spacing metrics get slightly skewed as well.  As a temporary work-around, I am generating larger glyphs and manually applying a box filter to down-sample the bitmaps to make them look like they should; however, this is not an acceptable final solution since it increases the processing time a little too much, and it can severely affect the glyph metrics used for kerning and spacing.

 

We have 3 other fonts we have been using in different applications that do not suffer from this, so I'm curious if there is anything we can do to alleviate this internally in Freetype, or if this font is too "detailed" for lower resolution bitmap generation.   If it helps, here is a snippet of our glyph/bitmap generation:

 

FT_Load_Glyph(m_Face, glyph_index, FT_LOAD_DEFAULT);

FT_Render_Glyph(glyph, FT_RENDER_MODE_NORMAL);

 

Thanks in advance if anyone has any ideas for how to alleviate this.

 

-Jordan

assuan_issues.JPG
Description: assuan_issues.JPG