Add nearest neighbour interpolation

Suitable for image enlargement

README.md

@@ -272,9 +272,10 @@ Use the given interpolator for image resizing, where `interpolator` is an attrib
 
 Possible interpolators, in order of performance, are:
 
-* `bilinear`: Use [bilinear interpolation](http://en.wikipedia.org/wiki/Bilinear_interpolation), the default (and fastest) interpolation.
+* `nearest`: Use [nearest neighbour interpolation](http://en.wikipedia.org/wiki/Nearest-neighbor_interpolation), suitable for image enlargement only.
+* `bilinear`: Use [bilinear interpolation](http://en.wikipedia.org/wiki/Bilinear_interpolation), the default and fastest image reduction interpolation.
 * `bicubic`: Use [bicubic interpolation](http://en.wikipedia.org/wiki/Bicubic_interpolation), which typically reduces performance by 5%.
-* `vertexSplitQuadraticBasisSpline`: Use [VSQBS interpolation](https://github.com/jcupitt/libvips/blob/master/libvips/resample/vsqbs.cpp#L48), which prevents "staircasing" when enlarging and typically reduces performance by 5%.
+* `vertexSplitQuadraticBasisSpline`: Use [VSQBS interpolation](https://github.com/jcupitt/libvips/blob/master/libvips/resample/vsqbs.cpp#L48), which prevents "staircasing" and typically reduces performance by 5%.
 * `locallyBoundedBicubic`: Use [LBB interpolation](https://github.com/jcupitt/libvips/blob/master/libvips/resample/lbb.cpp#L100), which prevents some "[acutance](http://en.wikipedia.org/wiki/Acutance)" and typically reduces performance by a factor of 2.
 * `nohalo`: Use [Nohalo interpolation](http://eprints.soton.ac.uk/268086/), which prevents acutance and typically reduces performance by a factor of 3.
 

index.js

@@ -139,6 +139,7 @@ Sharp.prototype.sharpen = function(sharpen) {
   Set the interpolator to use for the affine transformation
 */
 module.exports.interpolator = {
+  nearest: 'nearest',
   bilinear: 'bilinear',
   bicubic: 'bicubic',
   nohalo: 'nohalo',

package.json

@@ -1,6 +1,6 @@
 {
   "name": "sharp",
-  "version": "0.6.1",
+  "version": "0.6.2",
   "author": "Lovell Fuller <npm@lovell.info>",
   "contributors": [
     "Pierre Inglebert <pierre.inglebert@gmail.com>",
@@ -36,7 +36,7 @@
   ],
   "dependencies": {
     "nan": "^1.3.0",
-    "bluebird": "^2.3.1"
+    "bluebird": "^2.3.2"
   },
   "devDependencies": {
     "imagemagick": "^0.1.3",

tests/perf.js

@@ -185,6 +185,18 @@ async.series({
           }
         });
       }
+    }).add("sharp-file-buffer-nearest-neighbour", {
+      defer: true,
+      fn: function(deferred) {
+        sharp(inputJpg).resize(width, height).interpolateWith(sharp.interpolator.nearest).toBuffer(function(err, buffer) {
+          if (err) {
+            throw err;
+          } else {
+            assert.notStrictEqual(null, buffer);
+            deferred.resolve();
+          }
+        });
+      }
     }).add("sharp-file-buffer-bicubic", {
       defer: true,
       fn: function(deferred) {

tests/unit.js

@@ -247,6 +247,16 @@ async.series([
       done();
     });
   },
+  // Interpolation: nearest neighbour
+  function(done) {
+    sharp(inputJpg).resize(320, 240).interpolateWith(sharp.interpolator.nearest).toBuffer(function(err, data, info) {
+      if (err) throw err;
+      assert.strictEqual(true, data.length > 0);
+      assert.strictEqual(320, info.width);
+      assert.strictEqual(240, info.height);
+      done();
+    });
+  },
   // Interpolation: bilinear
   function(done) {
     sharp(inputJpg).resize(320, 240).interpolateWith(sharp.interpolator.bilinear).toBuffer(function(err, data, info) {