Add support for greyscale conversion #43

README.md

@@ -283,7 +283,7 @@ This is equivalent to GraphicsMagick's `>` geometry option: "change the dimensio
 
 #### sharpen()
 
-Perform a mild sharpen of the resultant image. This typically reduces performance by 30%.
+Perform a mild sharpen of the output image. This typically reduces performance by 10%.
 
 #### interpolateWith(interpolator)
 
@@ -308,6 +308,14 @@ This can improve the perceived brightness of a resized image in non-linear colou
 
 JPEG input images will not take advantage of the shrink-on-load performance optimisation when applying a gamma correction.
 
+#### grayscale() / greyscale()
+
+Convert to 8-bit greyscale; 256 shades of grey.
+
+This is a linear operation. If the input image is in a non-linear colourspace such as sRGB, use `gamma()` with `greyscale()` for the best results.
+
+The output image will still be web-friendly sRGB and contain three (identical) channels.
+
 ### Output options
 
 #### jpeg()
@@ -332,7 +340,7 @@ The output quality to use for lossy JPEG, WebP and TIFF output formats. The defa
 
 Use progressive (interlace) scan for JPEG and PNG output. This typically reduces compression performance by 30% but results in an image that can be rendered sooner when decompressed.
 
-#### withMetadata([boolean])
+#### withMetadata()
 
 Include all metadata (ICC, EXIF, XMP) from the input image in the output image. The default behaviour is to strip all metadata.
 

index.js

@@ -21,6 +21,7 @@ var Sharp = function(input) {
     sharpen: false,
     interpolator: 'bilinear',
     gamma: 0,
+    greyscale: false,
     progressive: false,
     sequentialRead: false,
     quality: 80,
@@ -181,6 +182,15 @@ Sharp.prototype.gamma = function(gamma) {
   return this;
 };
 
+/*
+  Convert to greyscale
+*/
+Sharp.prototype.greyscale = function(greyscale) {
+  this.options.greyscale = (typeof greyscale === 'boolean') ? greyscale : true;
+  return this;
+};
+Sharp.prototype.grayscale = Sharp.prototype.greyscale;
+
 Sharp.prototype.progressive = function(progressive) {
   this.options.progressive = (typeof progressive === 'boolean') ? progressive : true;
   return this;

src/sharp.cc

@@ -28,6 +28,7 @@ struct resize_baton {
   bool sharpen;
   std::string interpolator;
   double gamma;
+  bool greyscale;
   bool progressive;
   bool without_enlargement;
   VipsAccess access_method;
@@ -483,6 +484,16 @@ class ResizeWorker : public NanAsyncWorker {
       shrunk_on_load = gamma_encoded;
     }
 
+    // Convert to greyscale (linear, therefore after gamma encoding, if any)
+    if (baton->greyscale) {
+      VipsImage *greyscale = vips_image_new();
+      if (vips_colourspace(shrunk_on_load, &greyscale, VIPS_INTERPRETATION_B_W, NULL)) {
+        return resize_error(baton, shrunk_on_load);
+      }
+      g_object_unref(shrunk_on_load);
+      shrunk_on_load = greyscale;
+    }
+
     VipsImage *shrunk = vips_image_new();
     if (shrink > 1) {
       // Use vips_shrink with the integral reduction
@@ -750,6 +761,7 @@ NAN_METHOD(resize) {
   baton->sharpen = options->Get(NanNew<String>("sharpen"))->BooleanValue();
   baton->interpolator = *String::Utf8Value(options->Get(NanNew<String>("interpolator"))->ToString());
   baton->gamma = options->Get(NanNew<String>("gamma"))->NumberValue();
+  baton->greyscale = options->Get(NanNew<String>("greyscale"))->BooleanValue();
   baton->progressive = options->Get(NanNew<String>("progressive"))->BooleanValue();
   baton->without_enlargement = options->Get(NanNew<String>("withoutEnlargement"))->BooleanValue();
   baton->access_method = options->Get(NanNew<String>("sequentialRead"))->BooleanValue() ? VIPS_ACCESS_SEQUENTIAL : VIPS_ACCESS_RANDOM;

tests/perf.js

@@ -257,6 +257,30 @@ async.series({
           }
         });
       }
+    }).add("sharp-file-buffer-greyscale", {
+      defer: true,
+      fn: function(deferred) {
+        sharp(inputJpg).resize(width, height).greyscale().toBuffer(function(err, buffer) {
+          if (err) {
+            throw err;
+          } else {
+            assert.notStrictEqual(null, buffer);
+            deferred.resolve();
+          }
+        });
+      }
+    }).add("sharp-file-buffer-greyscale-gamma", {
+      defer: true,
+      fn: function(deferred) {
+        sharp(inputJpg).resize(width, height).gamma().greyscale().toBuffer(function(err, buffer) {
+          if (err) {
+            throw err;
+          } else {
+            assert.notStrictEqual(null, buffer);
+            deferred.resolve();
+          }
+        });
+      }
     }).add("sharp-file-buffer-progressive", {
       defer: true,
       fn: function(deferred) {

tests/unit.js

@@ -24,6 +24,8 @@ var inputPng = path.join(fixturesPath, "50020484-00001.png"); // http://c.searsp
 var inputWebP = path.join(fixturesPath, "4.webp"); // http://www.gstatic.com/webp/gallery/4.webp
 var inputGif = path.join(fixturesPath, "Crash_test.gif"); // http://upload.wikimedia.org/wikipedia/commons/e/e3/Crash_test.gif
 
+var outputZoinks = path.join(fixturesPath, 'output.zoinks'); // an "unknown" file extension
+
 // Ensure cache limits can be set
 sharp.cache(0); // Disable
 sharp.cache(50, 500); // 50MB, 500 items
@@ -425,6 +427,7 @@ async.series([
       anErrorWasEmitted = !!err;
     }).on('end', function() {
       assert(anErrorWasEmitted);
+      fs.unlinkSync(outputJpg);
       done();
     });
     var readableButNotAnImage = fs.createReadStream(__filename);
@@ -439,6 +442,7 @@ async.series([
       anErrorWasEmitted = !!err;
     }).on('end', function() {
       assert(anErrorWasEmitted);
+      fs.unlinkSync(outputJpg);
       done();
     });
     var writable = fs.createWriteStream(outputJpg);
@@ -522,44 +526,49 @@ async.series([
   },
   // Output filename without extension should mirror input format
   function(done) {
-    sharp(inputJpg).resize(320, 80).toFile(path.join(fixturesPath, 'output.zoinks'), function(err, info) {
+    sharp(inputJpg).resize(320, 80).toFile(outputZoinks, function(err, info) {
       if (err) throw err;
       assert.strictEqual('jpeg', info.format);
       assert.strictEqual(320, info.width);
       assert.strictEqual(80, info.height);
+      fs.unlinkSync(outputZoinks);
       done();
     });
   },
   function(done) {
-    sharp(inputPng).resize(320, 80).toFile(path.join(fixturesPath, 'output.zoinks'), function(err, info) {
+    sharp(inputPng).resize(320, 80).toFile(outputZoinks, function(err, info) {
       if (err) throw err;
       assert.strictEqual('png', info.format);
       assert.strictEqual(320, info.width);
       assert.strictEqual(80, info.height);
+      fs.unlinkSync(outputZoinks);
       done();
     });
   },
   function(done) {
-    sharp(inputWebP).resize(320, 80).toFile(path.join(fixturesPath, 'output.zoinks'), function(err, info) {
+    sharp(inputWebP).resize(320, 80).toFile(outputZoinks, function(err, info) {
       if (err) throw err;
       assert.strictEqual('webp', info.format);
       assert.strictEqual(320, info.width);
       assert.strictEqual(80, info.height);
+      fs.unlinkSync(outputZoinks);
       done();
     });
   },
   function(done) {
-    sharp(inputTiff).resize(320, 80).toFile(path.join(fixturesPath, 'output.zoinks'), function(err, info) {
+    sharp(inputTiff).resize(320, 80).toFile(outputZoinks, function(err, info) {
       if (err) throw err;
       assert.strictEqual('tiff', info.format);
       assert.strictEqual(320, info.width);
       assert.strictEqual(80, info.height);
+      fs.unlinkSync(outputZoinks);
       done();
     });
   },
   function(done) {
-    sharp(inputGif).resize(320, 80).toFile(path.join(fixturesPath, 'output.zoinks'), function(err, info) {
+    sharp(inputGif).resize(320, 80).toFile(outputZoinks, function(err, info) {
       assert(!!err);
+      done();
     });
   },
   // Metadata - JPEG
@@ -681,7 +690,7 @@ async.series([
   },
   // Gamma correction
   function(done) {
-    sharp(inputJpgWithGammaHoliness).resize(129, 111).toFile(path.join(fixturesPath, 'output.gamma-0.0.jpg'), function(err) {
+    sharp(inputJpgWithGammaHoliness).resize(129, 111).toFile(path.join(fixturesPath, 'output.gamma-0.0.jpg'), function(err, info) {
       if (err) throw err;
       done();
     });
@@ -698,6 +707,19 @@ async.series([
       done();
     });
   },
+  // Greyscale conversion
+  function(done) {
+    sharp(inputJpg).resize(320, 240).greyscale().toFile(path.join(fixturesPath, 'output.greyscale-gamma-0.0.jpg'), function(err, info) {
+      if (err) throw err;
+      done();
+    });
+  },
+  function(done) {
+    sharp(inputJpg).resize(320, 240).gamma().greyscale().toFile(path.join(fixturesPath, 'output.greyscale-gamma-2.2.jpg'), function(err) {
+      if (err) throw err;
+      done();
+    });
+  },
   // Verify internal counters
   function(done) {
     var counters = sharp.counters();