Autohint

Fontisan supports automatic hint generation for fonts without hints or when converting between formats.

Overview

Autohinting generates hint data automatically based on glyph outlines. This is useful when:

• Source font lacks hints
• Converting between incompatible hint systems
• Improving rendering quality

CLI Usage

# Enable autohinting during conversion
fontisan convert font.ttf --to otf --autohint --output font.otf

# With specific hinting mode
fontisan convert font.ttf --to otf --autohint --hinting-mode auto

API Usage

options = Fontisan::ConversionOptions.new(
  opening: { autohint: true },
  generating: { hinting_mode: "auto" }
)

converter = Fontisan::Converters::OutlineConverter.new
result = converter.convert(font, options: options)

Hinting Modes

Mode	Description	Use Case
preserve	Keep original hints	Same-format conversions
auto	Apply automatic hinting	Cross-format, missing hints
none	Remove all hints	Smallest file size
full	Full hint conversion	Maximum quality

When to Use Autohint

Use Autohint When:

• Converting TTF to OTF (different hint systems)
• Converting OTF to TTF (different hint systems)
• Source font has no hints
• Source hints are corrupt or incomplete

Don't Use Autohint When:

• Converting same format (TTF → TTF, OTF → OTF)
• Source has good TrueType instructions
• Source has good PostScript hints
• Target application doesn't use hints

Autohint Process

For TrueType Output

1. Analyze glyph outlines
2. Detect stem widths and positions
3. Generate CVT table with common values
4. Create prep program with basic setup
5. Leave fpgm empty (no glyph programs)

For OpenType Output

1. Analyze glyph outlines
2. Detect blue zones (baseline, x-height, cap height)
3. Detect stem widths
4. Generate Private DICT parameters
5. Create stem hints in CharStrings

Quality

Autohint Limitations

• No glyph-specific instructions — Only global hints
• May not match hand-tuned hints — Quality varies
• Better than no hints — Generally improves rendering

Comparison

Source	Autohint	Hand-Tuned
Quality	Good	Best
Consistency	High	Varies
Time	Fast	Slow
Cost	Free	Expensive

Examples

Convert with Autohint

# Type 1 to OTF with autohint
fontisan convert font.pfb --to otf --autohint --output font.otf

Remove and Regenerate Hints

# Remove existing hints, add autohints
fontisan convert font.ttf --to ttf --hinting-mode none --autohint --output font-rehinted.ttf

Batch Processing

Dir.glob('fonts/*.ttf').each do |input|
  output = input.sub('.ttf', '-hinted.ttf')
  options = Fontisan::ConversionOptions.new(
    opening: { autohint: true },
    generating: { hinting_mode: "auto" }
  )

  font = Fontisan::FontLoader.load(input)
  converter = Fontisan::Converters::OutlineConverter.new
  result = converter.convert(font, options: options)
  Fontisan::FontWriter.write(result, output)
end

Testing Hints

After autohinting, test rendering quality:

# Generate sample images at small sizes
fontisan render font-hinted.ttf --size 8 --output sample-8pt.png
fontisan render font-hinted.ttf --size 10 --output sample-10pt.png
fontisan render font-hinted.ttf --size 12 --output sample-12pt.png