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font-match v2: fingerprint the comp lettering and pick candidates from a Google Fonts catalog index

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lib/font-fingerprint.mjs replaces the three-number fingerprint with
size-invariant shape features (x-height ratio, stroke contrast, stem width,
run-length quantiles, roundness, serif signal, width spread) and a
noise-normalized distance; family recall on a held-out self-test rose from
13% to 72% top-5. data/font-index.json carries the whole Google Fonts
catalog (3,092 faces at two cap sizes, 707 KB); font-match --rank fingerprints
the comp crop, takes the 25 nearest faces from the index (plus the model's
own names), renders them at the comp's cap height, ranks by the same
distance, and prints a proof sheet and the CSS to use. scripts/build-font-
index.mjs rebuilds the index at release time.

AI-assisted (Claude).

Co-Authored-By: Claude <noreply@anthropic.com>
This commit is contained in:
Paul Bakaus
2026-08-28 06:13:59 +05:00
committed by Abdul Wahab
co-authored by Claude
parent cacb2868ac
commit 95294e464a
6 changed files with 330 additions and 7 deletions
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skill/scripts/lib/font-fingerprint.mjs
+10 -5
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@@ -62,8 +62,11 @@ const mean = (a) => (a.length ? a.reduce((s, x) => s + x, 0) / a.length : null);
/** Binarize; returns { W, H, ink: Uint8Array, inkIsDark }. */
function binarize(img) {
const g = toGray(img);
const thr = otsu(g);
let thr = otsu(g);
let dark = 0; for (let i = 0; i < g.data.length; i++) if (g.data[i] < thr) dark++;
// a two-level raster (no antialiasing) puts the Otsu threshold on the dark
// level itself; step it up so that level counts as ink
if (!dark) { thr += 1; for (let i = 0; i < g.data.length; i++) if (g.data[i] < thr) dark++; }
const inkIsDark = dark <= g.data.length / 2;
const ink = new Uint8Array(g.data.length);
let sI = 0, nI = 0, sG = 0, nG = 0;
@@ -319,15 +322,17 @@ function measure(bin, lines) {
}
/**
* fingerprint(img) -> features or null. Upsamples 2x (bilinear) when the
* fingerprint(img) -> features, or null when no lettering is found. Upsamples (bilinear) when the
* cap height is under 24px so runs and edges are measured on finer pixels.
*/
export function fingerprint(img, { minCap = 24 } = {}) {
export function fingerprint(img, { minCap = 24, minGlyphs = 3 } = {}) {
let bin = binarize(img);
let { lines } = findLines(bin);
if (!lines.length) return null;
let f = measure(bin, lines);
if (!f) return null;
// fewer than minGlyphs separable glyphs is not lettering (a rule, a solid
// bar, one letterform): callers read null as "no separable lettering"
if (!f || f.glyphs < minGlyphs) return null;
let scale = 1;
if (f.capHeightPx < minCap && f.capHeightPx >= 4) {
scale = Math.min(4, Math.ceil(minCap / f.capHeightPx));
@@ -338,7 +343,7 @@ export function fingerprint(img, { minCap = 24 } = {}) {
if (f2) f = f2;
else scale = 1;
}
const r = { lines: lines.length, glyphs: f.glyphs, capHeightPx: +(f.capHeightPx / scale).toFixed(1), inkIsDark: bin.inkIsDark, upsampled: scale > 1, allCaps: f.allCaps, weight: f.densTall ?? f.densX };
const r = { lines: lines.length, glyphs: f.glyphs, capHeightPx: +(f.capHeightPx / scale).toFixed(1), inkIsDark: bin.inkIsDark, upsampled: scale > 1, allCaps: f.allCaps, weight: f.densTall == null && f.densX == null ? null : +(f.densTall ?? f.densX).toFixed(4) };
for (const k of FEATURES) r[k] = f[k] == null ? null : +f[k].toFixed(4);
return r;
}