Ensure 16-bit+alpha input images work with vips_premultiply #301

Improves SVG support as *magick serves these as 16-bit

Add automated tests for SVG and 16-bit+alpha PNG inputs

test/fixtures/index.js

@@ -71,6 +71,7 @@ module.exports = {
   inputPngWithTransparency: getPath('blackbug.png'), // public domain
   inputPngWithGreyAlpha: getPath('grey-8bit-alpha.png'),
   inputPngWithOneColor: getPath('2x2_fdcce6.png'),
+  inputPngWithTransparency16bit: getPath('tbgn2c16.png'), // http://www.schaik.com/pngsuite/tbgn2c16.png
   inputPngOverlayLayer0: getPath('alpha-layer-0-background.png'),
   inputPngOverlayLayer1: getPath('alpha-layer-1-fill.png'),
   inputPngOverlayLayer2: getPath('alpha-layer-2-ink.png'),

test/unit/alpha.js

@@ -46,6 +46,19 @@ describe('Alpha transparency', function() {
       });
   });
 
+  it('Flatten 16-bit PNG with transparency to orange', function(done) {
+    sharp(fixtures.inputPngWithTransparency16bit)
+      .flatten()
+      .background({r: 255, g: 102, b: 0})
+      .toBuffer(function(err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(true, info.size > 0);
+        assert.strictEqual(32, info.width);
+        assert.strictEqual(32, info.height);
+        fixtures.assertSimilar(fixtures.expected('flatten-rgb16-orange.jpg'), data, done);
+      });
+  });
+
   it('Do not flatten', function(done) {
     sharp(fixtures.inputPngWithTransparency)
       .flatten(false)

test/unit/io.js

@@ -638,16 +638,17 @@ describe('Input/output', function() {
       sharp(fixtures.inputSvg)
         .resize(100, 100)
         .toFormat('png')
-        .toFile(fixtures.path('output.svg.png'), function(err, info) {
+        .toBuffer(function(err, data, info) {
           if (err) {
             assert.strictEqual(0, err.message.indexOf('Input file is of an unsupported image format'));
+            done();
           } else {
             assert.strictEqual(true, info.size > 0);
             assert.strictEqual('png', info.format);
             assert.strictEqual(100, info.width);
             assert.strictEqual(100, info.height);
+            fixtures.assertSimilar(fixtures.expected('svg.png'), data, done);
           }
-          done();
         });
     });
   }