Added optimizeTransparency to MagickImageCollection.

src/magick-image-collection.ts

@@ -242,6 +242,13 @@ export interface IMagickImageCollection extends Array<IMagickImage>, IDisposable
      * optimizePlus is exactly as optimize, but may also add or even remove extra frames in the
      * animation, if it improves the total number of pixels in the resulting GIF animation.
      */
+    optimizePlus(): void;
+
+    /**
+     * Compares each image the GIF disposed forms of the previous image in the sequence. Any
+     * pixel that does not change the displayed result is replaced with transparency.
+     */
+    optimizeTransparency(): void;
 
     /**
      * Read all image frames.
@@ -484,6 +491,16 @@ export class MagickImageCollection extends Array<MagickImage> implements IMagick
         });
     }
 
+    optimizeTransparency(): void {
+        this.throwIfEmpty();
+
+        this.attachImages(instance => {
+            Exception.usePointer(exception => {
+                ImageMagick._api._MagickImageCollection_OptimizeTransparency(instance, exception);
+            });
+        });
+    }
+
     read(fileName: string, settings?: MagickReadSettings): void;
     read(array: ByteArray, settings?: MagickReadSettings): void;
     read(fileNameOrArray: string | ByteArray, settings?: MagickReadSettings): void {

tests/magick-image-collection/optimize-transparency.spec.ts

@@ -0,0 +1,48 @@
+/*
+  Copyright Dirk Lemstra https://github.com/dlemstra/magick-wasm.
+  Licensed under the Apache License, Version 2.0.
+*/
+
+import { MagickColors } from '@src/magick-colors';
+import { MagickImage } from '@src/magick-image';
+import { TestImages } from '@test/test-images';
+
+describe('MagickImageCollection#optimizePlus', () => {
+    it('should throw exception when collection is empty', () => {
+        TestImages.emptyCollection.use((images) => {
+            expect(() => {
+                images.optimizeTransparency();
+            }).toThrowError('operation requires at least one image');
+        });
+    });
+
+    it('should make part of the images transparent', () => {
+        TestImages.emptyCollection.use((images) => {
+
+            images.push(MagickImage.create(MagickColors.Red, 1, 2));
+            images.push(MagickImage.create(MagickColors.Red, 1, 2));
+
+            const second = MagickImage.create(MagickColors.Red, 1, 1);
+            second.extent(1, 2, MagickColors.Green);
+            images.push(second);
+
+            images.optimizeTransparency();
+
+            expect(images.length).toBe(3);
+            expect(images[0].width).toBe(1);
+            expect(images[0].height).toBe(2);
+            expect(images[0]).toHavePixelWithColor(0, 0, '#ff0000ff');
+            expect(images[0]).toHavePixelWithColor(0, 1, '#ff0000ff');
+
+            expect(images[1].width).toBe(1);
+            expect(images[1].height).toBe(2);
+            expect(images[1]).toHavePixelWithColor(0, 0, '#ff000000');
+            expect(images[1]).toHavePixelWithColor(0, 1, '#ff000000');
+
+            expect(images[2].width).toBe(1);
+            expect(images[2].height).toBe(2);
+            expect(images[2]).toHavePixelWithColor(0, 0, '#ff000000');
+            expect(images[2]).toHavePixelWithColor(0, 1, '#008000ff');
+        });
+    });
+});