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Font hinting guides the adjustment of a scaled outline font to the target pixel grid before rasterization. In TrueType, instructions can control how outline points move at a particular size and resolution. Grid fitting can preserve important strokes when faithful geometric scaling would leave them awkwardly positioned between pixels.^[ref]

For an idealized example, two equal-width vertical strokes can overlap different fractions of neighboring pixels after scaling. Their rasterized darkness can then differ despite equal geometric widths. Coordinating the adjusted stroke positions and widths can make their displayed weights more consistent. The target depends on the requested size: a correction suitable for a small glyph need not be appropriate when many more pixels resolve its outline.

Font hinting changes the geometry used for rendering, rather than the underlying Unicode text or its grapheme clusters. Glyph substitution, glyph positioning and font hinting solve different parts of the path from encoded text to a visible image.

Grid fitting adjusts scaled glyph geometry relative to a target pixel grid before rasterization. TrueType font hinting can move outline points to preserve important strokes and alignment at small sizes. The result depends on the requested resolution and transformation.^[ref]

A simple area-coverage antialiasing model shows the problem. A vertical stroke from horizontal coordinate 0.4 to 1.6 covers 60 percent of each of two neighboring pixel columns. An equal-width stroke from 3.9 to 5.1 covers 10 percent, 100 percent and 10 percent of three columns. Both geometries have width 1.2 pixels, yet their darkest columns differ. Snapping their boundaries to give each stroke one full column changes the outlines but gives consistent displayed stroke weights.

This is a tradeoff between geometric fidelity and small-size legibility, rather than a change to the stored Unicode text. Grid fitting operates on the geometry supplied to the rasterization step; glyph substitution and glyph positioning address the forms and layout that precede it.

OpenType is a table-based computer font format separating glyph representations, character mapping, measurements, naming metadata and optional layout rules. Its cmap table selects default glyph indices for encoded text characters; substitution and positioning tables support more elaborate text shaping.

An OpenType computer font can contain TrueType outlines or Compact Font Format outlines, and the specification also provides for bitmap and other glyph representations. The file format therefore does not prescribe a single kind of outline geometry. Extensions such as .ttf and .otf are useful conventions, but the actual table contents determine the available representation.^[ref]

This organization lets one system answer separate questions: which glyph represents this text, how much space should it occupy, and how should it be drawn at this size? A language's contextual forms can change the first answer without changing the original Unicode text.

An outline font stores glyph shapes as geometric boundaries that can be scaled before drawing. Bézier curves provide editable segments of these boundaries. TrueType outlines use quadratic Bézier curves; Type 2 charstrings used in Compact Font Format outlines use cubic Bézier curves. ^{[ref] [ref]}

Scaling the boundary and choosing output pixels are separate operations. The rasterization step turns the scaled glyph geometry into a displayed image, so the same outline font can serve different output sizes without storing a separate image for every size.

TrueType is a computer font technology whose glyph outlines use quadratic Bézier curves and straight segments. The stored coordinates describe a scalable design in font units. Rendering scales that geometry to the requested size and applies rasterization to obtain pixels.

At small display sizes, geometrically accurate scaling can place important strokes between pixels. Font hinting supplies instructions that adjust the scaled outline relative to the output grid, helping preserve recognizable strokes and spacing. A small capital letter can therefore require more than shrinking a large image: the useful result depends on the relation between its geometry and the pixel grid.^[ref]

TrueType outlines can be stored in an OpenType computer font. The outline technology and the larger table-based file format describe different layers of the same rendering system.