Allow non-RGB input to embed/extend onto bg with alpha #646

docs/api-colour.md

@@ -3,7 +3,7 @@
 # background
 
 Set the background for the `embed`, `flatten` and `extend` operations.
-The default background is `{r: 0, g: 0, b: 0, a: 1}`, black without transparency.
+The default background is `{r: 0, g: 0, b: 0, alpha: 1}`, black without transparency.
 
 Delegates to the _color_ module, which can throw an Error
 but is liberal in what it accepts, clipping values to sensible min/max.

docs/changelog.md

@@ -37,6 +37,10 @@ Requires libvips v8.4.2.
   [#623](https://github.com/lovell/sharp/pull/623)
   [@ppaskaris](https://github.com/ppaskaris)
 
+* Allow non-RGB input to embed/extend onto background with an alpha channel.
+  [#646](https://github.com/lovell/sharp/issues/646)
+  [@DaGaMs](https://github.com/DaGaMs)
+
 ### v0.16 - "*pencil*"
 
 Requires libvips v8.3.3

lib/colour.js

@@ -29,7 +29,12 @@ const colourspace = {
  */
 const background = function background (rgba) {
   const colour = color(rgba);
-  this.options.background = colour.rgb().array().concat(colour.alpha() * 255);
+  this.options.background = [
+    colour.red(),
+    colour.green(),
+    colour.blue(),
+    Math.round(colour.alpha() * 255)
+  ];
   return this;
 };
 

package.json

@@ -61,7 +61,7 @@
   ],
   "dependencies": {
     "caw": "^2.0.0",
-    "color": "^1.0.1",
+    "color": "^1.0.2",
     "got": "^6.6.3",
     "nan": "^2.4.0",
     "semver": "^5.3.0",
@@ -71,7 +71,7 @@
     "async": "^2.1.4",
     "bufferutil": "^1.3.0",
     "cross-env": "^3.1.3",
-    "documentation": "^4.0.0-beta15",
+    "documentation": "^4.0.0-beta16",
     "exif-reader": "^1.0.1",
     "icc": "^0.0.2",
     "mocha": "^3.2.0",

src/common.cc

@@ -434,4 +434,20 @@ namespace sharp {
     );
   }
 
+  /*
+    Convert RGBA value to another colourspace
+  */
+  std::vector<double> GetRgbaAsColourspace(std::vector<double> const rgba, VipsInterpretation const interpretation) {
+    int const bands = static_cast<int>(rgba.size());
+    if (bands < 3 || interpretation == VIPS_INTERPRETATION_sRGB || interpretation == VIPS_INTERPRETATION_RGB) {
+      return rgba;
+    } else {
+      VImage pixel = VImage::new_matrix(1, 1);
+      pixel.set("bands", bands);
+      pixel = pixel.new_from_image(rgba);
+      pixel = pixel.colourspace(interpretation, VImage::option()->set("source_space", VIPS_INTERPRETATION_sRGB));
+      return pixel(0, 0);
+    }
+  }
+
 }  // namespace sharp

src/common.h

@@ -199,6 +199,11 @@ namespace sharp {
   */
   VipsInterpretation GetInterpretation(std::string const typeStr);
 
+  /*
+    Convert RGBA value to another colourspace
+  */
+  std::vector<double> GetRgbaAsColourspace(std::vector<double> const rgba, VipsInterpretation const interpretation);
+
 }  // namespace sharp
 
 #endif  // SRC_COMMON_H_

src/pipeline.cc

@@ -470,6 +470,8 @@ class PipelineWorker : public Nan::AsyncWorker {
           if (baton->background[3] < 255.0 || HasAlpha(image)) {
             background.push_back(baton->background[3] * multiplier);
           }
+          // Ensure background colour uses correct colourspace
+          background = sharp::GetRgbaAsColourspace(background, image.interpretation());
           // Add non-transparent alpha channel, if required
           if (baton->background[3] < 255.0 && !HasAlpha(image)) {
             image = image.bandjoin(
@@ -538,6 +540,8 @@ class PipelineWorker : public Nan::AsyncWorker {
         if (baton->background[3] < 255.0 || HasAlpha(image)) {
           background.push_back(baton->background[3] * multiplier);
         }
+        // Ensure background colour uses correct colourspace
+        background = sharp::GetRgbaAsColourspace(background, image.interpretation());
         // Add non-transparent alpha channel, if required
         if (baton->background[3] < 255.0 && !HasAlpha(image)) {
           image = image.bandjoin(
@@ -689,14 +693,13 @@ class PipelineWorker : public Nan::AsyncWorker {
         }
         image = image.extract_band(baton->extractChannel);
       }
-
       // Convert image to sRGB, if not already
       if (sharp::Is16Bit(image.interpretation())) {
         image = image.cast(VIPS_FORMAT_USHORT);
       }
       if (image.interpretation() != baton->colourspace) {
-        // Need to convert image
-        image = image.colourspace(baton->colourspace);
+        // Convert colourspace, pass the current known interpretation so libvips doesn't have to guess
+        image = image.colourspace(baton->colourspace, VImage::option()->set("source_space", image.interpretation()));
         // Transform colours from embedded profile to output profile
         if (baton->withMetadata &&
             sharp::HasProfile(image) &&

test/fixtures/index.js

@@ -83,6 +83,7 @@ module.exports = {
   inputWebP: getPath('4.webp'), // http://www.gstatic.com/webp/gallery/4.webp
   inputWebPWithTransparency: getPath('5_webp_a.webp'), // http://www.gstatic.com/webp/gallery3/5_webp_a.webp
   inputTiff: getPath('G31D.TIF'), // http://www.fileformat.info/format/tiff/sample/e6c9a6e5253348f4aef6d17b534360ab/index.htm
+  inputTiffCielab: getPath('cielab-dagams.tiff'), // https://github.com/lovell/sharp/issues/646
   inputGif: getPath('Crash_test.gif'), // http://upload.wikimedia.org/wikipedia/commons/e/e3/Crash_test.gif
   inputGifGreyPlusAlpha: getPath('grey-plus-alpha.gif'), // http://i.imgur.com/gZ5jlmE.gif
   inputSvg: getPath('check.svg'), // http://dev.w3.org/SVG/tools/svgweb/samples/svg-files/check.svg

test/unit/embed.js

@@ -22,7 +22,6 @@ describe('Embed', function () {
       });
   });
 
-  if (sharp.format.webp.output.buffer) {
   it('JPEG within WebP, to include alpha channel', function (done) {
     sharp(fixtures.inputJpg)
       .resize(320, 240)
@@ -39,7 +38,6 @@ describe('Embed', function () {
         fixtures.assertSimilar(fixtures.expected('embed-3-into-4.webp'), data, done);
       });
   });
-  }
 
   it('PNG with alpha channel', function (done) {
     sharp(fixtures.inputPngWithTransparency)
@@ -103,6 +101,23 @@ describe('Embed', function () {
       });
   });
 
+  it('embed TIFF in LAB colourspace onto RGBA background', function (done) {
+    sharp(fixtures.inputTiffCielab)
+      .resize(64, 128)
+      .embed()
+      .background({r: 255, g: 102, b: 0, alpha: 0.5})
+      .png()
+      .toBuffer(function (err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(true, data.length > 0);
+        assert.strictEqual('png', info.format);
+        assert.strictEqual(64, info.width);
+        assert.strictEqual(128, info.height);
+        assert.strictEqual(4, info.channels);
+        fixtures.assertSimilar(fixtures.expected('embed-lab-into-rgba.png'), data, done);
+      });
+  });
+
   it('Enlarge and embed', function (done) {
     sharp(fixtures.inputPngWithOneColor)
       .embed()