Resolution
Fax resolution: what each mode actually changes
Three definitions have coexisted since the 1980s. The choice is rarely made by hand, but it explains most documents that arrive unreadable.
Short answer
A fax is sent in one of three standardised definitions: standard, fine and superfine. They share the same horizontal fineness and differ only vertically. Doubling the vertical definition doubles the number of lines to transmit, and therefore roughly the length of the call.
Why only the vertical changes
Horizontal fineness is fixed by the sampling of the line: about eight points per millimetre, giving 1,728 points across a standardised width. The vertical figure depends on the paper advance step — the only parameter manufacturers ever varied. Hence definitions that always start with the same first number.
What the mode will never make up for
Definition does not compensate for a badly prepared document. A fax carries only black or white: grey text, a pale stamp or a colour photograph disappear at the thresholding stage, whatever fineness is chosen. Raising the definition of a document without contrast lengthens the call and improves nothing.
The three standardised definitions
| Standard — ordinary printed text | 204 × 98 ppp |
|---|---|
| Fine — the mode used here, by default | 204 × 196 ppp |
| Superfine — drawings, small type | 204 × 391 ppp |
Frequently asked questions
- Which definition should be used?
- Fine suits almost any printed document and remains the best compromise between legibility and duration. Superfine is justified only for very small type or fine linework, and not every machine accepts it.
- Does the definition degrade a crisp PDF?
- It constrains it. A vector PDF is reduced to a grid of pure black and white points: shades disappear, very fine strokes can break. A document designed in hard black on white passes through that step undamaged.
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