Fix FontForge Rendering Artifacts at Small Sizes

Rendering artifacts at small point sizes usually occur when a font's vector paths are improperly aligned to the pixel grid, suffer from winding order errors, or lack proper hinting instructions. This guide outlines how to identify and resolve rasterization glitches in FontForge by fixing outline geometry, standardizing grid coordinates, configuring alignment zones, and generating clean TrueType or PostScript hints to ensure sharp legibility on screens.

1. Correct Contour Direction

Incorrect winding directions cause the rasterizer to invert fills, creating missing holes or unexpected solid blocks at low resolutions.

  • Select all glyphs (Ctrl + A or Cmd + A).
  • Navigate to Element > Correct Direction.
  • FontForge will ensure outer contours run counter-clockwise and inner cutouts run clockwise (for TrueType) or vice versa (for PostScript).

2. Snap Points to the Integer Grid

Fractional coordinates force rasterizers to interpolate positions across pixels, resulting in blurry edges, uneven stem weights, and smudged counters at low point sizes.

  • Select your glyphs.
  • Go to Element > Round to Int.
  • Ensure that control points and off-curve handles snap to whole integer units to prevent fractional coordinate ambiguity during rasterization.

3. Remove Overlapping Paths and Redundant Nodes

Overlapping shapes might render fine at 72pt, but at 10pt or 12pt, the scan-conversion engine can miscalculate edge boundaries.

  • Select the affected glyphs.
  • Choose Element > Overlap > Remove Overlap (Ctrl + Shift + O).
  • Run Element > Simplify > Simplify to eliminate microscopic segments, duplicate nodes, or colinear points that destabilize rasterization algorithms.

4. Configure PostScript Alignment Zones (BlueValues)

For consistent heights across characters at small sizes, rasterizers rely on baseline, x-height, and cap-height alignment zones to snap horizontal edges to exact pixel boundaries.

  • Open Element > Font Info.
  • Navigate to PS Private Dictionary.
  • Define the BlueValues and OtherBlues arrays. Ensure alignment zones do not overlap and that each pair covers the flat tops and overshoot curves of corresponding character sets (e.g., flat top of 'x' versus curved top of 'o').

5. Generate and Refine Stem Hints

Without hinting, small-point rendering engines guess which vector lines represent prominent stems, leading to uneven vertical lines or missing strokes.

  • Autohinting: Select all glyphs and choose Hints > AutoHint. This automatically defines major horizontal and vertical stem widths.
  • Review Hints: Open a glyph in the outline view and enable View > Show > Hints. Ensure hints only cover structural stems, not decorative flourishes.
  • Hint Substitution: For complex glyphs where stems change across the shape, check Hints > AutoHint with Hints > Hint Substitution Pts enabled.

6. Address TrueType Instructions (TTF Hinting)

If exporting as TrueType (.ttf), PostScript hints must be converted to native TrueType instructions:

  • FontForge includes an internal TrueType instruction generator under Hints > Auto-Instruct.
  • For superior rendering in Windows environments (DirectWrite/ClearType), consider exporting an unhinted TrueType font and post-processing it with the external tool ttfautohint, which applies automated, high-quality grid-fitting instructions designed specifically for low-resolution displays.

7. Preview and Validate

Test the fixes directly inside FontForge before compiling:

  • Open the Metrics Window (Window > New Metrics Window).
  • Set the point size to the target low resolution (e.g., 9pt, 11pt, 14pt).
  • Toggle between rasterizer modes via View > Display Size or view rendered bitmaps to verify that stem thicknesses remain uniform and counter spaces remain open.