From e0d58266be05da72c1072c5c7048637113b172c0 Mon Sep 17 00:00:00 2001
From: Lovell Fuller <github@lovell.info>
Date: Thu, 14 Apr 2016 21:39:17 +0100
Subject: [PATCH] Allow use of embed with 1 and 2 channel images #411

---
 docs/changelog.md                         |   4 ++++
 src/pipeline.cc                           |  20 +++++++++++++++-----
 test/fixtures/expected/embed-2channel.png | Bin 0 -> 703 bytes
 test/unit/embed.js                        |  16 ++++++++++++++++
 test/unit/gamma.js                        |   4 ++--
 5 files changed, 37 insertions(+), 7 deletions(-)
 create mode 100644 test/fixtures/expected/embed-2channel.png

diff --git a/docs/changelog.md b/docs/changelog.md
index fd0c2d44..a0704ce9 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -12,6 +12,10 @@ Requires libvips v8.2.3
   [@anandthakker](https://github.com/anandthakker)
   [@kentongray](https://github.com/kentongray)
 
+* Allow use of embed with 1 and 2 channel images.
+  [#411](https://github.com/lovell/sharp/issues/411)
+  [@janaz](https://github.com/janaz)
+
 #### v0.14.0 - 2<sup>nd</sup> April 2016
 
 * Add ability to extend (pad) the edges of an image.
diff --git a/src/pipeline.cc b/src/pipeline.cc
index 43def594..35e23a49 100644
--- a/src/pipeline.cc
+++ b/src/pipeline.cc
@@ -496,11 +496,21 @@ class PipelineWorker : public AsyncWorker {
           // Scale up 8-bit values to match 16-bit input image
           double multiplier = (image.interpretation() == VIPS_INTERPRETATION_RGB16) ? 256.0 : 1.0;
           // Create background colour
-          std::vector<double> background {
-            baton->background[0] * multiplier,
-            baton->background[1] * multiplier,
-            baton->background[2] * multiplier
-          };
+          std::vector<double> background;
+          if (image.bands() > 2) {
+            background = {
+              multiplier * baton->background[0],
+              multiplier * baton->background[1],
+              multiplier * baton->background[2]
+            };
+          } else {
+            // Convert sRGB to greyscale
+            background = { multiplier * (
+              0.2126 * baton->background[0] +
+              0.7152 * baton->background[1] +
+              0.0722 * baton->background[2]
+            )};
+          }
           // Add alpha channel to background colour
           if (baton->background[3] < 255.0 || HasAlpha(image)) {
             background.push_back(baton->background[3] * multiplier);
diff --git a/test/fixtures/expected/embed-2channel.png b/test/fixtures/expected/embed-2channel.png
new file mode 100644
index 0000000000000000000000000000000000000000..ca6f220aef4133bf2f5c2e7b67af6eb5d9668291
GIT binary patch
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diff --git a/test/unit/embed.js b/test/unit/embed.js
index c459eb3f..32d91fad 100644
--- a/test/unit/embed.js
+++ b/test/unit/embed.js
@@ -88,6 +88,22 @@ describe('Embed', function() {
       });
   });
 
+  it('PNG with 2 channels', function(done) {
+    sharp(fixtures.inputPngWithGreyAlpha)
+      .resize(32, 16)
+      .embed()
+      .background({r: 0, g: 0, b: 0, a: 0})
+      .toBuffer(function(err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(true, data.length > 0);
+        assert.strictEqual('png', info.format);
+        assert.strictEqual(32, info.width);
+        assert.strictEqual(16, info.height);
+        assert.strictEqual(4, info.channels);
+        fixtures.assertSimilar(fixtures.expected('embed-2channel.png'), data, done);
+      });
+  });
+
   it('Enlarge and embed', function(done) {
     sharp(fixtures.inputPngWithOneColor)
       .embed()
diff --git a/test/unit/gamma.js b/test/unit/gamma.js
index 2779ad6e..252dce65 100644
--- a/test/unit/gamma.js
+++ b/test/unit/gamma.js
@@ -38,7 +38,7 @@ describe('Gamma correction', function() {
         assert.strictEqual('jpeg', info.format);
         assert.strictEqual(129, info.width);
         assert.strictEqual(111, info.height);
-        fixtures.assertSimilar(fixtures.expected('gamma-3.0.jpg'), data, done);
+        fixtures.assertSimilar(fixtures.expected('gamma-3.0.jpg'), data, { threshold: 6 }, done);
       });
   });
 
@@ -49,7 +49,7 @@ describe('Gamma correction', function() {
       .toBuffer(function(err, data, info) {
         assert.strictEqual('png', info.format);
         assert.strictEqual(320, info.width);
-        fixtures.assertSimilar(fixtures.expected('gamma-alpha.jpg'), data, done);
+        fixtures.assertSimilar(fixtures.expected('gamma-alpha.jpg'), data, { threshold: 11 }, done);
       });
   });