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mandy314 · 07-06-2014, 04:11 AM

Here some of my experiences with font's metrics and line-height:

Values for line-height computation are stored in different places within the font, mainly
-- WINAscent and WINDescent pair
-- hhea Ascender, hhea Descender and Line-Gap trio
-- Typo Ascender, Typo Descender and Typo Line-Gap trio

Afaik the Kindle (only ?) uses the hhea values but ignores the Line-Gap.

So for all practical purposes:
- check the EM Unit Size of your font (should be 1000 or 2048 - all other values are relative to the unit size)
- compare WINAscent/WINDescent with hhea Ascender/hhea Descender (should be identical in most cases but the hhea Descender must be a negative value)
- if your font has a Line-Gap>0 you may add the Line-Gap to the hhea Ascender and set the Line-Gap to zero

Font's metrics vary considerably - for example Times New Roman has a Caps-Height of 1341, Caecila of 1434 (both with 2048 EM Unit Size), so Caecilia is quite a bit larger than Times New Roman even with the same point size.
Concerning line-height some fonts (like Georgia or Droid) have "tight lines" (for example Georgia 2 with Asc=1878 and Desc=-449, which gives a line-height of 2327), other have "loose lines" (for example Caecilia with Asc=2183 and Desc=-559, which gives a line-height of 2742). To get some kind of comparison for the line-heights it may be feasible to compute the line-height/caps-height ratio: Georgia 2 has 1.64 / Caecila has 1.91.

If you want to edit the metrics of your font to look at the Kindle fonts may be a good starting point. Caecilia's Asc/Desc I've already mentioned, for Baskerville the values are 1907/-588.

Finally come caveats: I tried to fine-tune the line-height for some font lately and found there must be additional information (besides hhea values) used by the kindle as I lost a complete line on the page by reducing the asc by only 1 (some kind of threshold perhaps). Some fonts use the Y-Max/Y-Min for all glyphs as hhea values which may result in "large" line-heights (Charis with its extensive glyph set is an example for this). Some fonts may be converted from/to TTF/OTF etc and the values may be screwed up. But besides the Line-Gap thing I always would give the original font's metric a chance. All this has been tested on PW1 with FW 5.3.9.

07-06-2014, 04:11 AM	#216
mandy314 Connoisseur Posts: 71 Karma: 200092 Join Date: Mar 2014 Device: kindle pw1	Here some of my experiences with font's metrics and line-height: Values for line-height computation are stored in different places within the font, mainly -- WINAscent and WINDescent pair -- hhea Ascender, hhea Descender and Line-Gap trio -- Typo Ascender, Typo Descender and Typo Line-Gap trio Afaik the Kindle (only ?) uses the hhea values but ignores the Line-Gap. So for all practical purposes: - check the EM Unit Size of your font (should be 1000 or 2048 - all other values are relative to the unit size) - compare WINAscent/WINDescent with hhea Ascender/hhea Descender (should be identical in most cases but the hhea Descender must be a negative value) - if your font has a Line-Gap>0 you may add the Line-Gap to the hhea Ascender and set the Line-Gap to zero Font's metrics vary considerably - for example Times New Roman has a Caps-Height of 1341, Caecila of 1434 (both with 2048 EM Unit Size), so Caecilia is quite a bit larger than Times New Roman even with the same point size. Concerning line-height some fonts (like Georgia or Droid) have "tight lines" (for example Georgia 2 with Asc=1878 and Desc=-449, which gives a line-height of 2327), other have "loose lines" (for example Caecilia with Asc=2183 and Desc=-559, which gives a line-height of 2742). To get some kind of comparison for the line-heights it may be feasible to compute the line-height/caps-height ratio: Georgia 2 has 1.64 / Caecila has 1.91. If you want to edit the metrics of your font to look at the Kindle fonts may be a good starting point. Caecilia's Asc/Desc I've already mentioned, for Baskerville the values are 1907/-588. Finally come caveats: I tried to fine-tune the line-height for some font lately and found there must be additional information (besides hhea values) used by the kindle as I lost a complete line on the page by reducing the asc by only 1 (some kind of threshold perhaps). Some fonts use the Y-Max/Y-Min for all glyphs as hhea values which may result in "large" line-heights (Charis with its extensive glyph set is an example for this). Some fonts may be converted from/to TTF/OTF etc and the values may be screwed up. But besides the Line-Gap thing I always would give the original font's metric a chance. All this has been tested on PW1 with FW 5.3.9.