Switch default interpolator to bicubic #289

Only use gaussian blur for non-linear interpolators

Improves performance of bilinear by ~15%

Add liborc to the packaged build to improve bicubic perf

Add examples of the various interpolation methods

Add bilinear vs bicubic to perf tests

test/interpolators/README.md

@@ -0,0 +1,48 @@
+# Interpolators
+
+[Photo](https://www.flickr.com/photos/aotaro/21978966091) by
+[aotaro](https://www.flickr.com/photos/aotaro/) is licensed under
+[CC BY 2.0](https://creativecommons.org/licenses/by/2.0/).
+
+The following examples take the 4608x3072px original image
+and resize to 480x320px using various interpolators.
+
+To fetch the original 4608x3072px image and
+generate the interpolator sample images:
+
+```sh
+curl -O https://farm6.staticflickr.com/5682/21978966091_b421afe866_o.jpg
+node generate.js
+```
+
+## Nearest neighbour
+
+![Nearest neighbour interpolation](nearest.jpg)
+
+## Bilinear
+
+![Bilinear interpolation](bilinear.jpg)
+
+## Bicubic
+
+![Bicubic interpolation](bicubic.jpg)
+
+## Locally bounded bicubic
+
+![Locally bounded bicubic interpolation](lbb.jpg)
+
+## Vertex-split quadratic b-splines (VSQBS)
+
+![Vertex-split quadratic b-splines interpolation](vsqbs.jpg)
+
+## Nohalo
+
+![Nohalo interpolation](nohalo.jpg)
+
+## GraphicsMagick
+
+![GraphicsMagick](gm.jpg)
+
+```sh
+gm convert 21978966091_b421afe866_o.jpg -resize 480x320^ -gravity center -extent 480x320 -quality 95 -strip -define jpeg:optimize-coding=true gm.jpg
+```

test/interpolators/generate.js

@@ -0,0 +1,11 @@
+'use strict';
+
+['nearest', 'bilinear', 'bicubic', 'vsqbs', 'lbb', 'nohalo'].forEach(function(interpolator) {
+  require('../../')('21978966091_b421afe866_o.jpg')
+    .resize(480, 320)
+    .interpolateWith(interpolator)
+    .quality(95)
+    .toFile(interpolator + '.jpg', function(err) {
+      if (err) throw err;
+    });
+});

test/unit/gamma.js

@@ -16,7 +16,7 @@ describe('Gamma correction', function() {
         assert.strictEqual('jpeg', info.format);
         assert.strictEqual(129, info.width);
         assert.strictEqual(111, info.height);
-        fixtures.assertSimilar(fixtures.expected('gamma-0.0.jpg'), data, {threshold: 12}, done);
+        fixtures.assertSimilar(fixtures.expected('gamma-0.0.jpg'), data, done);
       });
   });