Fix tint op by ensuring LAB and allowing negative values #1235

Add test cases for more tint colours and input interpretations

docs/changelog.md

@@ -4,6 +4,12 @@
 
 Requires libvips v8.6.1.
 
+#### v0.20.3 - TBD
+
+* Fix tint operation by ensuring LAB interpretation and allowing negative values.
+  [#1235](https://github.com/lovell/sharp/issues/1235)
+  [@wezside](https://github.com/wezside)
+
 #### v0.20.2 - 28<sup>th</sup> April 2018
 
 * Add tint operation to set image chroma.

lib/constructor.js

@@ -152,8 +152,8 @@ const Sharp = function (input, options) {
     fastShrinkOnLoad: true,
     // operations
     background: [0, 0, 0, 255],
-    tintA: 0,
-    tintB: 0,
+    tintA: 128,
+    tintB: 128,
     flatten: false,
     negate: false,
     medianSize: 0,

src/operations.cc

@@ -161,13 +161,14 @@ namespace sharp {
     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);
+    std::vector<double> chroma {a, b};
+    VImage tinted = luminance
+      .bandjoin(chroma)
+      .copy(VImage::option()->set("interpretation", VIPS_INTERPRETATION_LAB))
+      .colourspace(typeBeforeTint);
     // Attach original alpha channel, if any
     if (HasAlpha(image)) {
       // Extract original alpha channel

src/pipeline.cc

@@ -683,7 +683,7 @@ class PipelineWorker : public Nan::AsyncWorker {
       }
 
       // Tint the image
-      if (baton->tintA > 0 || baton->tintB > 0) {
+      if (baton->tintA < 128.0 || baton->tintB < 128.0) {
         image = sharp::Tint(image, baton->tintA, baton->tintB);
       }
 

src/pipeline.h

@@ -157,8 +157,8 @@ struct PipelineBaton {
     cropOffsetLeft(0),
     cropOffsetTop(0),
     premultiplied(false),
-    tintA(0.0),
-    tintB(0.0),
+    tintA(128.0),
+    tintB(128.0),
     flatten(false),
     negate(false),
     blurSigma(0.0),

test/unit/tint.js

@@ -19,6 +19,32 @@ describe('Tint', function () {
       });
   });
 
+  it('tints rgb image green', function (done) {
+    const output = fixtures.path('output.tint-green.jpg');
+    sharp(fixtures.inputJpg)
+      .resize(320, 240)
+      .tint('#00FF00')
+      .toFile(output, function (err, info) {
+        if (err) throw err;
+        assert.strictEqual(true, info.size > 0);
+        fixtures.assertMaxColourDistance(output, fixtures.expected('tint-green.jpg'), 10);
+        done();
+      });
+  });
+
+  it('tints rgb image blue', function (done) {
+    const output = fixtures.path('output.tint-blue.jpg');
+    sharp(fixtures.inputJpg)
+      .resize(320, 240)
+      .tint('#0000FF')
+      .toFile(output, function (err, info) {
+        if (err) throw err;
+        assert.strictEqual(true, info.size > 0);
+        fixtures.assertMaxColourDistance(output, fixtures.expected('tint-blue.jpg'), 10);
+        done();
+      });
+  });
+
   it('tints rgb image with sepia tone', function (done) {
     const output = fixtures.path('output.tint-sepia.jpg');
     sharp(fixtures.inputJpg)
@@ -60,4 +86,17 @@ describe('Tint', function () {
         done();
       });
   });
+
+  it('tints cmyk image red', function (done) {
+    const output = fixtures.path('output.tint-cmyk.jpg');
+    sharp(fixtures.inputJpgWithCmykProfile)
+      .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-cmyk.jpg'), 10);
+        done();
+      });
+  });
 });