similarity (#396)

* feat: alignMinDifference returns the similarity

* feat: add getNbNonZeroPixels method in Mask

Author: lpatiny

src/Mask.ts

@@ -327,6 +327,20 @@ export class Mask {
     this.data[index * this.channels] = result;
   }
 
+  /**
+   * Get the number of pixels that do not have the value 0.
+   * @returns
+   */
+  public getNbNonZeroPixels(): number {
+    let count = 0;
+    for (const datum of this.data) {
+      if (datum) {
+        count++;
+      }
+    }
+    return count;
+  }
+
   /**
    * Get the value of a bit. Function exists for compatibility with Image.
    * @param column - Column index.

src/__tests__/Mask.test.ts

@@ -62,6 +62,7 @@ describe('get and set bit', () => {
     expect(mask.getValueByPoint(point)).toBe(0);
     mask.setValueByPoint(point, 1);
     expect(mask.getValueByPoint(point)).toBe(1);
+    expect(mask.getNbNonZeroPixels()).toBe(1);
   });
 });
 
@@ -109,6 +110,7 @@ test('fill with a value', () => {
     [1, 1],
     [1, 1],
   ]);
+  expect(mask.getNbNonZeroPixels()).toBe(4);
 });
 
 test('createFrom', () => {

src/align/__tests__/alignMinDifference.test.ts

@@ -10,7 +10,7 @@ test('1 pixel source', () => {
   ]);
 
   const result = alignMinDifference(source, destination);
-  expect(result).toStrictEqual({ row: 2, column: 1 });
+  expect(result).toStrictEqual({ row: 2, column: 1, similarity: 1 });
 });
 
 test('4 pixels source', () => {
@@ -25,7 +25,11 @@ test('4 pixels source', () => {
   ]);
 
   const result = alignMinDifference(source, destination);
-  expect(result).toStrictEqual({ row: 1, column: 1 });
+  expect(result).toStrictEqual({
+    row: 1,
+    column: 1,
+    similarity: 0.8235294117647058,
+  });
 });
 
 test('twice same image', () => {
@@ -34,7 +38,7 @@ test('twice same image', () => {
   const destination = testUtils.load('opencv/test.png').grey();
 
   const result = alignMinDifference(source, destination);
-  expect(result).toStrictEqual({ row: 0, column: 0 });
+  expect(result).toStrictEqual({ row: 0, column: 0, similarity: 1 });
 });
 
 test('source too big', () => {
@@ -61,7 +65,7 @@ test('larger image and crop', () => {
 
   const result = alignMinDifference(source, destination);
 
-  expect(result).toStrictEqual(origin);
+  expect(result).toStrictEqual({ ...origin, similarity: 1 });
 });
 
 test('larger image and crop 2', () => {
@@ -72,7 +76,7 @@ test('larger image and crop 2', () => {
 
   const result = alignMinDifference(source, destination);
 
-  expect(result).toStrictEqual(origin);
+  expect(result).toStrictEqual({ ...origin, similarity: 1 });
 });
 
 test('id crops', () => {

src/align/alignMinDifference.ts

@@ -1,4 +1,4 @@
-import { Image, Mask, Point } from '..';
+import { Image, Mask } from '..';
 import checkProcessable from '../utils/validators/checkProcessable';
 
 export interface AlignMinDifferenceOptions {
@@ -23,7 +23,7 @@ export function alignMinDifference(
   source: Image,
   destination: Image,
   options: AlignMinDifferenceOptions = {},
-): Point {
+) {
   checkProcessable(source, { components: 1, bitDepth: [8, 16], alpha: false });
 
   const xSpan = destination.width - source.width;
@@ -51,6 +51,13 @@ export function alignMinDifference(
   let startY = 0;
   let endX = xSpan;
   let endY = ySpan;
+
+  if (mask && mask.size !== source.size) {
+    throw new Error('Mask size must be equal to source size');
+  }
+
+  const nbPixelsToCheck = mask ? mask.getNbNonZeroPixels() : source.size;
+
   while (step >= 1) {
     step = Math.round(step);
 
@@ -94,5 +101,9 @@ export function alignMinDifference(
     endY = Math.round(Math.min(ySpan, bestShiftY + step));
   }
 
-  return { row: bestShiftY, column: bestShiftX };
+  return {
+    row: bestShiftY,
+    column: bestShiftX,
+    similarity: 1 - bestDifference / (nbPixelsToCheck * source.maxValue),
+  };
 }