fix: drop glare holes before the margin and never auto-pick specks

Filtering holes after the margin let -2 mm grow 1 mm specks past the
3 mm cutoff, and could drop real holes shrunk by a positive margin.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/lib/app-state.svelte.ts

@@ -9,6 +9,7 @@ import type { Point, RasterImage, Shape } from './types';
 export type Tool = 'none' | 'scale' | 'seed' | 'draw';
 
 const DEFAULT_THRESHOLD = 128;
+const MIN_HOLE_MM = 3;
 
 export class AppState {
   // Raw: the cv module and pixel buffers must never be wrapped in reactive proxies.
@@ -43,7 +44,10 @@ export class AppState {
     if (this.mode === 'manual') {
       return shapeFromPolygons(cv, image.width, image.height, { outer: this.manualOuter, holes: this.manualHoles }, this.marginPx);
     }
-    return detect(cv, image, { threshold: this.threshold, invert: this.invert, seed: this.seed, marginPx: this.marginPx });
+    return detect(cv, image, {
+      threshold: this.threshold, invert: this.invert, seed: this.seed, marginPx: this.marginPx,
+      minHolePx: this.pxPerMm ? MIN_HOLE_MM * this.pxPerMm : 0,
+    });
   });
 
   exportShape = $derived(this.shapePx && this.pxPerMm ? prepareForExport(this.shapePx, this.pxPerMm) : null);

src/lib/detect.ts

@@ -100,6 +100,7 @@ export function detect(cv: CV, image: RasterImage, params: DetectParams): Shape
     const lab = labels.data32S;
     const m = mask.data;
     for (let i = 0; i < lab.length; i++) m[i] = lab[i] === label ? 255 : 0;
+    fillSmallHoles(cv, mask, params.minHolePx);
     return traceMask(cv, mask, params.marginPx);
   } finally {
     gray.delete();
@@ -134,16 +135,41 @@ function pickComponent(
     }
   }
 
+  // Without a click, specks (dust, grain) must never pass as the piece.
+  const minArea = 0.01 * width * height;
   let best: number | null = null;
   let bestArea = 0;
   for (let label = 1; label < count; label++) {
     const b = box(label);
     if (b.left === 0 || b.top === 0 || b.right === width || b.bottom === height) continue;
     const area = stat(label, cv.CC_STAT_AREA);
-    if (area > bestArea) {
+    if (area >= minArea && area > bestArea) {
       bestArea = area;
       best = label;
     }
   }
   return best;
 }
+
+/** Fill holes under minHolePx in both directions, before the margin can grow them. */
+function fillSmallHoles(cv: CV, mask: Mat, minHolePx: number) {
+  if (minHolePx <= 0) return;
+  const contours = new cv.MatVector();
+  const hierarchy = new cv.Mat();
+  try {
+    cv.findContours(mask, contours, hierarchy, cv.RETR_CCOMP, cv.CHAIN_APPROX_SIMPLE);
+    const h = hierarchy.data32S;
+    for (let i = 0; i < contours.size(); i++) {
+      if (h[i * 4 + 3] === -1) continue;
+      const c = contours.get(i);
+      const rect = cv.boundingRect(c);
+      c.delete();
+      if (rect.width < minHolePx && rect.height < minHolePx) {
+        cv.drawContours(mask, contours, i, new cv.Scalar(255), cv.FILLED);
+      }
+    }
+  } finally {
+    contours.delete();
+    hierarchy.delete();
+  }
+}

src/lib/geometry.ts

@@ -2,8 +2,6 @@ import type { Point, Shape } from './types';
 
 export type Bounds = { minX: number; minY: number; maxX: number; maxY: number };
 
-const MIN_HOLE_MM = 3;
-
 export function bounds(points: Point[]): Bounds {
   let minX = Infinity, minY = Infinity, maxX = -Infinity, maxY = -Infinity;
   for (const p of points) {
@@ -70,11 +68,7 @@ export function prepareForExport(shapePx: Shape, pxPerMm: number, toleranceMm =
     simplifyRing(ring.map((p) => ({ x: p.x / pxPerMm, y: p.y / pxPerMm })), toleranceMm);
   const outer = toMm(shapePx.outer);
   if (outer.length < 3) return null;
-  const holes = shapePx.holes.map(toMm).filter((hole) => {
+  const holes = shapePx.holes.map(toMm).filter((hole) => hole.length >= 3);
-    if (hole.length < 3) return false;
-    const { width, height } = shapeSize({ outer: hole, holes: [] });
-    return width >= MIN_HOLE_MM || height >= MIN_HOLE_MM;
-  });
   const { minX, minY } = bounds(outer);
   const shift = (ring: Point[]) => ring.map((p) => ({ x: p.x - minX, y: p.y - minY }));
   return { outer: shift(outer), holes: holes.map(shift) };

src/lib/types.ts

@@ -12,4 +12,6 @@ export type DetectParams = {
   seed: Point | null;
   /** Negative shrinks the piece (and grows holes). */
   marginPx: number;
+  /** Holes smaller than this in both directions are treated as glare and filled. */
+  minHolePx: number;
 };

tests/detect.test.ts

@@ -11,7 +11,7 @@ beforeAll(async () => {
 });
 
 const params = (overrides: Partial<DetectParams> = {}): DetectParams => ({
-  threshold: 128, invert: false, seed: null, marginPx: 0, ...overrides,
+  threshold: 128, invert: false, seed: null, marginPx: 0, minHolePx: 0, ...overrides,
 });
 
 /** Light plate x 40..159, y 30..129 with hole r=15 at (100,80), plus a small light blob, on dark ground. */
@@ -84,4 +84,23 @@ describe('detect', () => {
     });
     expect(detect(cv, speckled, params())!.holes).toHaveLength(0);
   });
+
+  it('fills specks smaller than minHolePx before the margin can grow them', () => {
+    const glare = grayImage(200, 160, (x, y) => {
+      const plate = inRect(x, y, 40, 30, 160, 130) && !inCircle(x, y, 100, 80, 15) && !inCircle(x, y, 60, 50, 3);
+      return plate ? 220 : 30;
+    });
+    expect(detect(cv, glare, params({ marginPx: -6 }))!.holes).toHaveLength(2);
+    expect(detect(cv, glare, params({ marginPx: -6, minHolePx: 10 }))!.holes).toHaveLength(1);
+  });
+
+  it('keeps a long thin hole that is under minHolePx in only one direction', () => {
+    const slotted = grayImage(200, 160, (x, y) => (inRect(x, y, 40, 30, 160, 130) && !inRect(x, y, 60, 60, 120, 66) ? 220 : 30));
+    expect(detect(cv, slotted, params({ minHolePx: 10 }))!.holes).toHaveLength(1);
+  });
+
+  it('does not auto-pick a speck when the real piece touches the border', () => {
+    const framed = grayImage(400, 300, (x, y) => (inRect(x, y, 0, 60, 240, 260) || inRect(x, y, 330, 100, 340, 110) ? 220 : 30));
+    expect(detect(cv, framed, params())).toBeNull();
+  });
 });

tests/fixtures.test.ts

@@ -34,7 +34,7 @@ describe.skipIf(cases.length === 0)('detect on real photos', () => {
   it.each(cases)('$file', (c) => {
     const image = readJpeg(dir + c.file);
     const threshold = c.threshold ?? otsuThreshold(cv, image);
-    const shape = detect(cv, image, { threshold, invert: c.invert, seed: c.seed, marginPx: 0 });
+    const shape = detect(cv, image, { threshold, invert: c.invert, seed: c.seed, marginPx: 0, minHolePx: 3 * c.pxPerMm });
     expect(shape).not.toBeNull();
     const mm = prepareForExport(shape!, c.pxPerMm)!;
     const size = shapeSize(mm);

tests/geometry.test.ts

@@ -53,20 +53,9 @@ describe('prepareForExport', () => {
     expect(mm.outer).toHaveLength(4);
   });
 
-  it('drops holes smaller than 3 mm in both directions (glare/speckle)', () => {
+  it('keeps every hole, however small (speck filtering happens before the margin)', () => {
-    const shapePx = {
+    const shapePx = { outer: denseSquare(0, 0, 400), holes: [denseSquare(100, 100, 8), denseSquare(200, 200, 40)] };
-      outer: denseSquare(0, 0, 400),
+    expect(prepareForExport(shapePx, 4)!.holes).toHaveLength(2);
-      holes: [denseSquare(100, 100, 8), denseSquare(200, 200, 40)], // 2 mm and 10 mm at 4 px/mm
-    };
-    const mm = prepareForExport(shapePx, 4)!;
-    expect(mm.holes).toHaveLength(1);
-    expect(shapeSize({ outer: mm.holes[0], holes: [] }).width).toBeCloseTo(10);
-  });
-
-  it('keeps a long thin hole that is under 3 mm in only one direction', () => {
-    const slot: Point[] = [{ x: 100, y: 100 }, { x: 300, y: 100 }, { x: 300, y: 104 }, { x: 100, y: 104 }];
-    const mm = prepareForExport({ outer: denseSquare(0, 0, 400), holes: [slot] }, 4)!;
-    expect(mm.holes).toHaveLength(1);
   });
 
   it('returns null when the outer ring degenerates', () => {