Release Scan Tools v0.1.0

tests/scan/pixels.test.ts

@@ -0,0 +1,61 @@
+import { describe, expect, it } from "vitest";
+import {
+  adjustPixels,
+  estimateDeskew,
+  luminance,
+  otsuThreshold,
+} from "../../src/scan/pixels";
+
+function rgba(values: number[]) {
+  return new Uint8ClampedArray(
+    values.flatMap((value) => [value, value, value, 255]),
+  );
+}
+
+describe("document pixels", () => {
+  it("uses perceptual luminance", () => {
+    expect(luminance(255, 0, 0)).toBe(54);
+    expect(luminance(0, 255, 0)).toBe(182);
+    expect(luminance(0, 0, 255)).toBe(18);
+  });
+
+  it("finds a separating Otsu threshold", () => {
+    const threshold = otsuThreshold(rgba([5, 10, 15, 230, 240, 250]));
+    expect(threshold).toBeGreaterThanOrEqual(15);
+    expect(threshold).toBeLessThan(230);
+  });
+
+  it("creates an opaque black-and-white page", () => {
+    expect([
+      ...adjustPixels(rgba([20, 220]), {
+        colourMode: "threshold",
+        threshold: 100,
+        brightness: 0,
+        contrast: 0,
+      }),
+    ]).toEqual([0, 0, 0, 255, 255, 255, 255, 255]);
+  });
+
+  it("does not invent skew in an empty page", () => {
+    expect(estimateDeskew(rgba(new Array(20 * 20).fill(255)), 20, 20)).toBe(0);
+  });
+
+  it("returns the corrective angle for tilted text lines", () => {
+    const width = 120;
+    const height = 90;
+    const data = rgba(new Array(width * height).fill(255));
+    const slope = Math.tan((3 * Math.PI) / 180);
+    for (const baseline of [24, 44, 64]) {
+      for (let x = 8; x < width - 8; x += 1) {
+        const y = Math.round(baseline + (x - width / 2) * slope);
+        for (let thickness = -1; thickness <= 1; thickness += 1) {
+          const index = ((y + thickness) * width + x) * 4;
+          data[index] = 0;
+          data[index + 1] = 0;
+          data[index + 2] = 0;
+        }
+      }
+    }
+    expect(estimateDeskew(data, width, height)).toBeCloseTo(-3, 0);
+  });
+});