Add convolve operation for kernel-based convolution (#479)

test/fixtures/index.js

@@ -91,6 +91,9 @@ module.exports = {
 
   inputJPGBig: getPath('flowers.jpeg'),
 
+  inputPngStripesV: getPath('stripesV.png'),
+  inputPngStripesH: getPath('stripesH.png'),
+
   outputJpg: getPath('output.jpg'),
   outputPng: getPath('output.png'),
   outputWebP: getPath('output.webp'),

test/unit/convolve.js

@@ -0,0 +1,82 @@
+'use strict';
+
+var assert = require('assert');
+
+var sharp = require('../../index');
+var fixtures = require('../fixtures');
+
+describe('Convolve', function() {
+
+  it('specific convolution kernel 1', function(done) {
+    sharp(fixtures.inputPngStripesV)
+      .resize(320, 240)
+      .convolve(
+        {
+          'width': 3,
+          'height': 3,
+          'scale': 50,
+          'offset': 0,
+          'kernel': [ 10, 20, 10,
+                      0,   0,  0,
+                      10, 20, 10 ]
+        })
+      .toBuffer(function(err, data, info) {
+        assert.strictEqual('png', info.format);
+        assert.strictEqual(320, info.width);
+        assert.strictEqual(240, info.height);
+        fixtures.assertSimilar(fixtures.expected('conv-1.png'), data, done);
+      });
+  });
+
+  it('specific convolution kernel 2', function(done) {
+    sharp(fixtures.inputPngStripesH)
+      .resize(320, 240)
+      .convolve(
+        {
+          'width': 3,
+          'height': 3,
+          'kernel': [ 1, 0, 1,
+                      2, 0, 2,
+                      1, 0, 1 ]
+        })
+      .toBuffer(function(err, data, info) {
+        assert.strictEqual('png', info.format);
+        assert.strictEqual(320, info.width);
+        assert.strictEqual(240, info.height);
+        fixtures.assertSimilar(fixtures.expected('conv-2.png'), data, done);
+      });
+  });
+
+  it('invalid kernel specification: no data', function() {
+    assert.throws(function() {
+      sharp(fixtures.inputJpg).convolve(
+        {
+          'width': 3,
+          'height': 3,
+          'kernel': []
+        });
+    });
+  });
+
+  it('invalid kernel specification: bad data format', function() {
+    assert.throws(function() {
+      sharp(fixtures.inputJpg).convolve(
+        {
+          'width': 3,
+          'height': 3,
+          'kernel': [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
+        });
+    });
+  });
+  
+  it('invalid kernel specification: wrong width', function() {
+    assert.throws(function() {
+      sharp(fixtures.inputJpg).convolve(
+        {
+          'width': 3,
+          'height': 4,
+          'kernel': [1, 2, 3, 4, 5, 6, 7, 8, 9]
+        });
+    });
+  });
+});