Add chroma subsampling options for JPEG output

README.md

@@ -438,6 +438,15 @@ Include all metadata (EXIF, XMP, IPTC) from the input image in the output image.
 
 The default behaviour is to strip all metadata and convert to the device-independent sRGB colour space.
 
+#### withoutChromaSubsampling()
+
+Disable the use of [chroma subsampling](http://en.wikipedia.org/wiki/Chroma_subsampling) with JPEG output (4:4:4).
+
+This can improve colour representation at higher quality settings (90+),
+but usually increases output file size and typically reduces performance by 25%.
+
+The default behaviour is to use chroma subsampling (4:2:0).
+
 #### compressionLevel(compressionLevel)
 
 An advanced setting for the _zlib_ compression level of the lossless PNG output format. The default level is `6`.

index.js

@@ -64,6 +64,7 @@ var Sharp = function(input) {
     quality: 80,
     compressionLevel: 6,
     withoutAdaptiveFiltering: false,
+    withoutChromaSubsampling: false,
     streamOut: false,
     withMetadata: false
   };
@@ -368,6 +369,14 @@ Sharp.prototype.withoutAdaptiveFiltering = function(withoutAdaptiveFiltering) {
   return this;
 };
 
+/*
+  Disable the use of chroma subsampling for JPEG output
+*/
+Sharp.prototype.withoutChromaSubsampling = function(withoutChromaSubsampling) {
+  this.options.withoutChromaSubsampling = (typeof withoutChromaSubsampling === 'boolean') ? withoutChromaSubsampling : true;
+  return this;
+};
+
 Sharp.prototype.withMetadata = function(withMetadata) {
   this.options.withMetadata = (typeof withMetadata === 'boolean') ? withMetadata : true;
   return this;

package.json

@@ -34,10 +34,10 @@
     "vips"
   ],
   "dependencies": {
-    "bluebird": "^2.9.8",
+    "bluebird": "^2.9.9",
     "color": "^0.7.3",
     "nan": "^1.6.2",
-    "semver": "^4.2.2"
+    "semver": "^4.3.0"
   },
   "devDependencies": {
     "mocha": "^2.1.0",

src/resize.cc

@@ -90,6 +90,7 @@ struct ResizeBaton {
   int quality;
   int compressionLevel;
   bool withoutAdaptiveFiltering;
+  bool withoutChromaSubsampling;
   std::string err;
   bool withMetadata;
 
@@ -117,6 +118,7 @@ struct ResizeBaton {
     quality(80),
     compressionLevel(6),
     withoutAdaptiveFiltering(false),
+    withoutChromaSubsampling(false),
     withMetadata(false) {
       background[0] = 0.0;
       background[1] = 0.0;
@@ -675,7 +677,8 @@ class ResizeWorker : public NanAsyncWorker {
     if (baton->output == "__jpeg" || (baton->output == "__input" && inputImageType == ImageType::JPEG)) {
       // Write JPEG to buffer
       if (vips_jpegsave_buffer(image, &baton->bufferOut, &baton->bufferOutLength, "strip", !baton->withMetadata,
-        "Q", baton->quality, "optimize_coding", TRUE, "interlace", baton->progressive, NULL)) {
+        "Q", baton->quality, "optimize_coding", TRUE, "no_subsample", baton->withoutChromaSubsampling,
+        "interlace", baton->progressive, NULL)) {
         return Error(baton, hook);
       }
       baton->outputFormat = "jpeg";
@@ -741,7 +744,8 @@ class ResizeWorker : public NanAsyncWorker {
       if (outputJpeg || (matchInput && inputImageType == ImageType::JPEG)) {
         // Write JPEG to file
         if (vips_jpegsave(image, baton->output.c_str(), "strip", !baton->withMetadata,
-          "Q", baton->quality, "optimize_coding", TRUE, "interlace", baton->progressive, NULL)) {
+          "Q", baton->quality, "optimize_coding", TRUE, "no_subsample", baton->withoutChromaSubsampling,
+          "interlace", baton->progressive, NULL)) {
           return Error(baton, hook);
         }
         baton->outputFormat = "jpeg";
@@ -992,6 +996,7 @@ NAN_METHOD(resize) {
   baton->quality = options->Get(NanNew<String>("quality"))->Int32Value();
   baton->compressionLevel = options->Get(NanNew<String>("compressionLevel"))->Int32Value();
   baton->withoutAdaptiveFiltering = options->Get(NanNew<String>("withoutAdaptiveFiltering"))->BooleanValue();
+  baton->withoutChromaSubsampling = options->Get(NanNew<String>("withoutChromaSubsampling"))->BooleanValue();
   baton->withMetadata = options->Get(NanNew<String>("withMetadata"))->BooleanValue();
   // Output filename or __format for Buffer
   baton->output = *String::Utf8Value(options->Get(NanNew<String>("output"))->ToString());

test/bench/package.json

@@ -12,7 +12,7 @@
     "imagemagick-native": "^1.7.0",
     "gm": "^1.17.0",
     "async": "^0.9.0",
-    "semver": "^4.2.0",
+    "semver": "^4.3.0",
     "benchmark": "^1.0.0"
   },
   "license": "Apache 2.0",

test/bench/perf.js

@@ -347,6 +347,18 @@ async.series({
           }
         });
       }
+    }).add('sharp-without-chroma-subsampling', {
+      defer: true,
+      fn: function(deferred) {
+        sharp(inputJpgBuffer).resize(width, height).withoutChromaSubsampling().toBuffer(function(err, buffer) {
+          if (err) {
+            throw err;
+          } else {
+            assert.notStrictEqual(null, buffer);
+            deferred.resolve();
+          }
+        });
+      }
     }).add('sharp-rotate', {
       defer: true,
       fn: function(deferred) {

test/unit/io.js

@@ -459,6 +459,35 @@ describe('Input/output', function() {
 
   });
 
+  it('Without chroma subsampling generates larger file', function(done) {
+    // First generate with chroma subsampling (default)
+    sharp(fixtures.inputJpg)
+      .resize(320, 240)
+      .withoutChromaSubsampling(false)
+      .toBuffer(function(err, withChromaSubsamplingData, withChromaSubsamplingInfo) {
+        if (err) throw err;
+        assert.strictEqual(true, withChromaSubsamplingData.length > 0);
+        assert.strictEqual(withChromaSubsamplingData.length, withChromaSubsamplingInfo.size);
+        assert.strictEqual('jpeg', withChromaSubsamplingInfo.format);
+        assert.strictEqual(320, withChromaSubsamplingInfo.width);
+        assert.strictEqual(240, withChromaSubsamplingInfo.height);
+        // Then generate without
+        sharp(fixtures.inputJpg)
+          .resize(320, 240)
+          .withoutChromaSubsampling()
+          .toBuffer(function(err, withoutChromaSubsamplingData, withoutChromaSubsamplingInfo) {
+            if (err) throw err;
+            assert.strictEqual(true, withoutChromaSubsamplingData.length > 0);
+            assert.strictEqual(withoutChromaSubsamplingData.length, withoutChromaSubsamplingInfo.size);
+            assert.strictEqual('jpeg', withoutChromaSubsamplingInfo.format);
+            assert.strictEqual(320, withoutChromaSubsamplingInfo.width);
+            assert.strictEqual(240, withoutChromaSubsamplingInfo.height);
+            assert.strictEqual(true, withChromaSubsamplingData.length < withoutChromaSubsamplingData.length);
+            done();
+          });
+      });
+  });
+
   it('Convert SVG, if supported, to PNG', function(done) {
     sharp(fixtures.inputSvg)
       .resize(100, 100)