Add tint operation to set image chroma

Rik Heywood · lovell · commit dbac4b9a634e · 2018-04-11T20:05:48.000+01:00
diff --git a/docs/api-colour.md b/docs/api-colour.md
@@ -3,10 +3,11 @@
 ### Table of Contents
 
 -   [background][1]
--   [greyscale][2]
--   [grayscale][3]
--   [toColourspace][4]
--   [toColorspace][5]
+-   [tint][2]
+-   [greyscale][3]
+-   [grayscale][4]
+-   [toColourspace][5]
+-   [toColorspace][6]
 
 ## background
 
@@ -19,10 +20,24 @@ The alpha value is a float between `0` (transparent) and `1` (opaque).
 
 **Parameters**
 
--   `rgba` **([String][6] \| [Object][7])** parsed by the [color][8] module to extract values for red, green, blue and alpha.
+-   `rgba` **([String][7] \| [Object][8])** parsed by the [color][9] module to extract values for red, green, blue and alpha.
 
 
--   Throws **[Error][9]** Invalid parameter
+-   Throws **[Error][10]** Invalid parameter
+
+Returns **Sharp** 
+
+## tint
+
+Tint the image using the provided chroma while preserving the image luminance.
+An alpha channel may be present and will be unchanged by the operation.
+
+**Parameters**
+
+-   `rgb` **([String][7] \| [Object][8])** parsed by the [color][9] module to extract chroma values.
+
+
+-   Throws **[Error][10]** Invalid parameter
 
 Returns **Sharp** 
 
@@ -37,7 +52,7 @@ An alpha channel may be present, and will be unchanged by the operation.
 
 **Parameters**
 
--   `greyscale` **[Boolean][10]**  (optional, default `true`)
+-   `greyscale` **[Boolean][11]**  (optional, default `true`)
 
 Returns **Sharp** 
 
@@ -47,7 +62,7 @@ Alternative spelling of `greyscale`.
 
 **Parameters**
 
--   `grayscale` **[Boolean][10]**  (optional, default `true`)
+-   `grayscale` **[Boolean][11]**  (optional, default `true`)
 
 Returns **Sharp** 
 
@@ -58,10 +73,10 @@ By default output image will be web-friendly sRGB, with additional channels inte
 
 **Parameters**
 
--   `colourspace` **[String][6]?** output colourspace e.g. `srgb`, `rgb`, `cmyk`, `lab`, `b-w` [...][11]
+-   `colourspace` **[String][7]?** output colourspace e.g. `srgb`, `rgb`, `cmyk`, `lab`, `b-w` [...][12]
 
 
--   Throws **[Error][9]** Invalid parameters
+-   Throws **[Error][10]** Invalid parameters
 
 Returns **Sharp** 
 
@@ -71,31 +86,33 @@ Alternative spelling of `toColourspace`.
 
 **Parameters**
 
--   `colorspace` **[String][6]?** output colorspace.
+-   `colorspace` **[String][7]?** output colorspace.
 
 
--   Throws **[Error][9]** Invalid parameters
+-   Throws **[Error][10]** Invalid parameters
 
 Returns **Sharp** 
 
 [1]: #background
 
-[2]: #greyscale
+[2]: #tint
+
+[3]: #greyscale
 
-[3]: #grayscale
+[4]: #grayscale
 
-[4]: #tocolourspace
+[5]: #tocolourspace
 
-[5]: #tocolorspace
+[6]: #tocolorspace
 
-[6]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String
+[7]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/String
 
-[7]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
+[8]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object
 
-[8]: https://www.npmjs.org/package/color
+[9]: https://www.npmjs.org/package/color
 
-[9]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Error
+[10]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Error
 
-[10]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean
+[11]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Boolean
 
-[11]: https://github.com/jcupitt/libvips/blob/master/libvips/iofuncs/enumtypes.c#L568
+[12]: https://github.com/jcupitt/libvips/blob/master/libvips/iofuncs/enumtypes.c#L568
diff --git a/docs/changelog.md b/docs/changelog.md
@@ -4,6 +4,12 @@
 
 Requires libvips v8.6.1.
 
+#### v0.20.2 - TBD
+
+* Add tint operation to set image chroma.
+  [#825](https://github.com/lovell/sharp/pull/825)
+  [@rikh42](https://github.com/rikh42)
+
 #### v0.20.1 - 17<sup>th</sup> March 2018
 
 * Improve installation experience when a globally-installed libvips below the minimum required version is found.
diff --git a/lib/colour.js b/lib/colour.js
@@ -38,6 +38,21 @@ function background (rgba) {
   return this;
 }
 
+/**
+ * Tint the image using the provided chroma while preserving the image luminance.
+ * An alpha channel may be present and will be unchanged by the operation.
+ *
+ * @param {String|Object} rgb - parsed by the [color](https://www.npmjs.org/package/color) module to extract chroma values.
+ * @returns {Sharp}
+ * @throws {Error} Invalid parameter
+ */
+function tint (rgb) {
+  const colour = color(rgb);
+  this.options.tintA = colour.a();
+  this.options.tintB = colour.b();
+  return this;
+}
+
 /**
  * Convert to 8-bit greyscale; 256 shades of grey.
  * This is a linear operation. If the input image is in a non-linear colour space such as sRGB, use `gamma()` with `greyscale()` for the best results.
@@ -95,6 +110,7 @@ module.exports = function (Sharp) {
   // Public instance functions
   [
     background,
+    tint,
     greyscale,
     grayscale,
     toColourspace,
diff --git a/lib/constructor.js b/lib/constructor.js
@@ -151,6 +151,8 @@ const Sharp = function (input, options) {
     fastShrinkOnLoad: true,
     // operations
     background: [0, 0, 0, 255],
+    tintA: 0,
+    tintB: 0,
     flatten: false,
     negate: false,
     medianSize: 0,
diff --git a/package.json b/package.json
@@ -45,7 +45,8 @@
     "Kenric D'Souza <kenric.dsouza@gmail.com>",
     "Oleh Aleinyk <oleg.aleynik@gmail.com>",
     "Marcel Bretschneider <marcel.bretschneider@gmail.com>",
-    "Andrea Bianco <andrea.bianco@unibas.ch>"
+    "Andrea Bianco <andrea.bianco@unibas.ch>",
+    "Rik Heywood <rik@rik.org>"
   ],
   "scripts": {
     "install": "(node install/libvips && node install/dll-copy && prebuild-install) || (node-gyp rebuild && node install/dll-copy)",
diff --git a/src/operations.cc b/src/operations.cc
@@ -152,6 +152,32 @@ namespace sharp {
     return dst.bandjoin(mask.cast(dst.format()));
   }
 
+  /*
+   * Tint an image using the specified chroma, preserving the original image luminance
+   */
+  VImage Tint(VImage image, double const a, double const b) {
+    // Get original colourspace
+    VipsInterpretation typeBeforeTint = image.interpretation();
+    if (typeBeforeTint == VIPS_INTERPRETATION_RGB) {
+      typeBeforeTint = VIPS_INTERPRETATION_sRGB;
+    }
+    // Create 2 band image with every pixel set to the tint chroma
+    std::vector<double> chromaPixel {a, b};
+    VImage chroma = image.new_from_image(chromaPixel);
+    // Extract luminance
+    VImage luminance = image.colourspace(VIPS_INTERPRETATION_LAB)[0];
+    // Create the tinted version by combining the L from the original and the chroma from the tint
+    VImage tinted = luminance.bandjoin(chroma).colourspace(typeBeforeTint);
+    // Attach original alpha channel, if any
+    if (HasAlpha(image)) {
+      // Extract original alpha channel
+      VImage alpha = image[image.bands() - 1];
+      // Join alpha channel to normalised image
+      tinted = tinted.bandjoin(alpha);
+    }
+    return tinted;
+  }
+
   /*
    * Stretch luminance to cover full dynamic range.
    */
diff --git a/src/operations.h b/src/operations.h
@@ -46,6 +46,11 @@ namespace sharp {
   */
   VImage Cutout(VImage src, VImage dst, const int gravity);
 
+  /*
+   * Tint an image using the specified chroma, preserving the original image luminance
+   */
+  VImage Tint(VImage image, double const a, double const b);
+
   /*
    * Stretch luminance to cover full dynamic range.
    */
diff --git a/src/pipeline.cc b/src/pipeline.cc
@@ -682,6 +682,11 @@ class PipelineWorker : public Nan::AsyncWorker {
         image = sharp::Bandbool(image, baton->bandBoolOp);
       }
 
+      // Tint the image
+      if (baton->tintA > 0 || baton->tintB > 0) {
+        image = sharp::Tint(image, baton->tintA, baton->tintB);
+      }
+
       // Extract an image channel (aka vips band)
       if (baton->extractChannel > -1) {
         if (baton->extractChannel >= image.bands()) {
@@ -1167,6 +1172,9 @@ NAN_METHOD(pipeline) {
   for (unsigned int i = 0; i < 4; i++) {
     baton->background[i] = AttrTo<double>(background, i);
   }
+  // Tint chroma
+  baton->tintA = AttrTo<double>(options, "tintA");
+  baton->tintB = AttrTo<double>(options, "tintB");
   // Overlay options
   if (HasAttr(options, "overlay")) {
     baton->overlay = CreateInputDescriptor(AttrAs<v8::Object>(options, "overlay"), buffersToPersist);
diff --git a/src/pipeline.h b/src/pipeline.h
@@ -70,6 +70,8 @@ struct PipelineBaton {
   std::string kernel;
   bool fastShrinkOnLoad;
   double background[4];
+  double tintA;
+  double tintB;
   bool flatten;
   bool negate;
   double blurSigma;
@@ -155,6 +157,8 @@ struct PipelineBaton {
     cropOffsetLeft(0),
     cropOffsetTop(0),
     premultiplied(false),
+    tintA(0.0),
+    tintB(0.0),
     flatten(false),
     negate(false),
     blurSigma(0.0),
diff --git a/test/fixtures/2569067123_aca715a2ee_o.png b/test/fixtures/2569067123_aca715a2ee_o.png
diff --git a/test/fixtures/expected/tint-alpha.png b/test/fixtures/expected/tint-alpha.png
diff --git a/test/fixtures/expected/tint-red.jpg b/test/fixtures/expected/tint-red.jpg
diff --git a/test/fixtures/expected/tint-sepia.jpg b/test/fixtures/expected/tint-sepia.jpg
diff --git a/test/fixtures/index.js b/test/fixtures/index.js
@@ -89,6 +89,7 @@ module.exports = {
   inputPngTestJoinChannel: getPath('testJoinChannel.png'),
   inputPngTruncated: getPath('truncated.png'), // gm convert 2569067123_aca715a2ee_o.jpg -resize 320x240 saw.png ; head -c 10000 saw.png > truncated.png
   inputPngEmbed: getPath('embedgravitybird.png'), // Released to sharp under a CC BY 4.0
+  inputPngRGBWithAlpha: getPath('2569067123_aca715a2ee_o.png'), // http://www.flickr.com/photos/grizdave/2569067123/ (same as inputJpg)
 
   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
diff --git a/test/unit/tint.js b/test/unit/tint.js
@@ -0,0 +1,63 @@
+'use strict';
+
+const assert = require('assert');
+
+const sharp = require('../../');
+const fixtures = require('../fixtures');
+
+describe('Tint', function () {
+  it('tints rgb image red', function (done) {
+    const output = fixtures.path('output.tint-red.jpg');
+    sharp(fixtures.inputJpg)
+      .resize(320, 240)
+      .tint('#FF0000')
+      .toFile(output, function (err, info) {
+        if (err) throw err;
+        assert.strictEqual(true, info.size > 0);
+        fixtures.assertMaxColourDistance(output, fixtures.expected('tint-red.jpg'), 10);
+        done();
+      });
+  });
+
+  it('tints rgb image with sepia tone', function (done) {
+    const output = fixtures.path('output.tint-sepia.jpg');
+    sharp(fixtures.inputJpg)
+      .resize(320, 240)
+      .tint('#704214')
+      .toFile(output, function (err, info) {
+        if (err) throw err;
+        assert.strictEqual(320, info.width);
+        assert.strictEqual(240, info.height);
+        fixtures.assertMaxColourDistance(output, fixtures.expected('tint-sepia.jpg'), 10);
+        done();
+      });
+  });
+
+  it('tints rgb image with sepia tone with rgb colour', function (done) {
+    const output = fixtures.path('output.tint-sepia.jpg');
+    sharp(fixtures.inputJpg)
+      .resize(320, 240)
+      .tint([112, 66, 20])
+      .toFile(output, function (err, info) {
+        if (err) throw err;
+        assert.strictEqual(320, info.width);
+        assert.strictEqual(240, info.height);
+        fixtures.assertMaxColourDistance(output, fixtures.expected('tint-sepia.jpg'), 10);
+        done();
+      });
+  });
+
+  it('tints rgb image with alpha channel', function (done) {
+    const output = fixtures.path('output.tint-alpha.png');
+    sharp(fixtures.inputPngRGBWithAlpha)
+      .resize(320, 240)
+      .tint('#704214')
+      .toFile(output, function (err, info) {
+        if (err) throw err;
+        assert.strictEqual(320, info.width);
+        assert.strictEqual(240, info.height);
+        fixtures.assertMaxColourDistance(output, fixtures.expected('tint-alpha.png'), 10);
+        done();
+      });
+  });
+});
