Improve performance and accuracy of multi-image composite #2286

docs/changelog.md

@@ -4,6 +4,11 @@
 
 Requires libvips v8.12.2
 
+### v0.30.2 - TBD
+
+* Improve performance and accuracy when compositing multiple images.
+  [#2286](https://github.com/lovell/sharp/issues/2286)
+
 ### v0.30.1 - 9th February 2022
 
 * Allow use of `toBuffer` and `toFile` on the same instance.

lib/composite.js

@@ -162,7 +162,6 @@ function composite (images) {
         throw is.invalidParameterError('premultiplied', 'boolean', image.premultiplied);
       }
     }
-
     return composite;
   });
   return this;

src/pipeline.cc

@@ -581,6 +581,8 @@ class PipelineWorker : public Napi::AsyncWorker {
 
       // Composite
       if (shouldComposite) {
+        std::vector<VImage> images = { image };
+        std::vector<int> modes, xs, ys;
         for (Composite *composite : baton->composite) {
           VImage compositeImage;
           sharp::ImageType compositeImageType = sharp::ImageType::UNKNOWN;
@@ -626,12 +628,12 @@ class PipelineWorker : public Napi::AsyncWorker {
             // gravity was used for extract_area, set it back to its default value of 0
             composite->gravity = 0;
           }
-          // Ensure image to composite is sRGB with premultiplied alpha
+          // Ensure image to composite is sRGB with unpremultiplied alpha
           compositeImage = compositeImage.colourspace(VIPS_INTERPRETATION_sRGB);
           if (!sharp::HasAlpha(compositeImage)) {
             compositeImage = sharp::EnsureAlpha(compositeImage, 1);
           }
-          if (!composite->premultiplied) compositeImage = compositeImage.premultiply();
+          if (composite->premultiplied) compositeImage = compositeImage.unpremultiply();
           // Calculate position
           int left;
           int top;
@@ -649,12 +651,12 @@ class PipelineWorker : public Napi::AsyncWorker {
             std::tie(left, top) = sharp::CalculateCrop(image.width(), image.height(),
               compositeImage.width(), compositeImage.height(), composite->gravity);
           }
-          // Composite
-          image = image.composite2(compositeImage, composite->mode, VImage::option()
-            ->set("premultiplied", TRUE)
-            ->set("x", left)
-            ->set("y", top));
+          images.push_back(compositeImage);
+          modes.push_back(composite->mode);
+          xs.push_back(left);
+          ys.push_back(top);
         }
+        image = image.composite(images, modes, VImage::option()->set("x", xs)->set("y", ys));
       }
 
       // Reverse premultiplication after all transformations:

test/unit/composite.js

@@ -45,22 +45,20 @@ const blends = [
 
 // Test
 describe('composite', () => {
-  it('blend', () => Promise.all(
-    blends.map(blend => {
+  blends.forEach(blend => {
+    it(`blend ${blend}`, async () => {
       const filename = `composite.blend.${blend}.png`;
       const actual = fixtures.path(`output.${filename}`);
       const expected = fixtures.expected(filename);
-      return sharp(redRect)
+      await sharp(redRect)
         .composite([{
           input: blueRect,
           blend
         }])
-        .toFile(actual)
-        .then(() => {
-          fixtures.assertMaxColourDistance(actual, expected);
-        });
-    })
-  ));
+        .toFile(actual);
+      fixtures.assertMaxColourDistance(actual, expected);
+    });
+  });
 
   it('premultiplied true', () => {
     const filename = 'composite.premultiplied.png';
@@ -121,22 +119,20 @@ describe('composite', () => {
       });
   });
 
-  it('multiple', () => {
+  it('multiple', async () => {
     const filename = 'composite-multiple.png';
     const actual = fixtures.path(`output.${filename}`);
     const expected = fixtures.expected(filename);
-    return sharp(redRect)
+    await sharp(redRect)
       .composite([{
         input: blueRect,
         gravity: 'northeast'
       }, {
         input: greenRect,
         gravity: 'southwest'
       }])
-      .toFile(actual)
-      .then(() => {
-        fixtures.assertMaxColourDistance(actual, expected);
-      });
+      .toFile(actual);
+    fixtures.assertMaxColourDistance(actual, expected);
   });
 
   it('zero offset', done => {

test/unit/extend.js

@@ -140,7 +140,7 @@ describe('Extend', function () {
   });
 
   it('Premultiply background when compositing', async () => {
-    const background = '#bf1942cc';
+    const background = { r: 191, g: 25, b: 66, alpha: 0.8 };
     const data = await sharp({
       create: {
         width: 1, height: 1, channels: 4, background: '#fff0'
@@ -158,10 +158,6 @@ describe('Extend', function () {
       })
       .raw()
       .toBuffer();
-    const [r1, g1, b1, a1, r2, g2, b2, a2] = data;
-    assert.strictEqual(true, Math.abs(r2 - r1) < 2);
-    assert.strictEqual(true, Math.abs(g2 - g1) < 2);
-    assert.strictEqual(true, Math.abs(b2 - b1) < 2);
-    assert.strictEqual(true, Math.abs(a2 - a1) < 2);
+    assert.deepStrictEqual(Array.from(data), [191, 25, 65, 204, 238, 31, 82, 204]);
   });
 });