Add support for PNG format. Close #2.

README.md

@@ -7,9 +7,9 @@ _adj_
 3. shrewd or astute: a sharp bargainer. 
 4. (Informal.) very stylish: a sharp dresser; a sharp jacket. 
 
-The typical use case for this high speed Node.js module is to convert a large JPEG image to smaller JPEG images of varying dimensions.
+The typical use case for this high speed Node.js module is to convert large JPEG and PNG images to smaller JPEG and PNG images of varying dimensions.
 
-It is somewhat opinionated in that it only deals with JPEG images, always obeys the requested dimensions by either cropping or embedding and insists on a mild sharpen of the resulting image.
+It is somewhat opinionated in that it only deals with JPEG and PNG images, always obeys the requested dimensions by either cropping or embedding and insists on a mild sharpen of the resulting image.
 
 Under the hood you'll find the blazingly fast [libvips](https://github.com/jcupitt/libvips) image processing library, originally created in 1989 at Birkbeck College and currently maintained by the University of Southampton.
 
@@ -19,7 +19,7 @@ Performance is 4x-8x faster than ImageMagick and 2x-4x faster than GraphicsMagic
 
 * Node.js v0.8+
 * node-gyp
-* libvips-dev 7.28+
+* libvips-dev 7.28+ (7.36+ for optimal JPEG Huffman coding)
 
 ```
 sudo npm install -g node-gyp
@@ -40,7 +40,7 @@ When installed as a package, please symlink `vips-7.28.pc` (or later, installed
 
 ### crop(inputPath, outputPath, width, height, callback)
 
-Scale and crop JPEG `inputPath` to `width` x `height` and write JPEG to `outputPath` calling `callback` when complete.
+Scale and crop `inputPath` to `width` x `height` and write to `outputPath` calling `callback` when complete.
 
 Example:
 
@@ -56,29 +56,29 @@ sharp.crop("input.jpg", "output.jpg", 300, 200, function(err) {
 
 ### embedWhite(inputPath, outputPath, width, height, callback)
 
-Scale and embed JPEG `inputPath` to `width` x `height` using a white canvas and write JPEG to `outputPath` calling `callback` when complete.
+Scale and embed `inputPath` to `width` x `height` using a white canvas and write to `outputPath` calling `callback` when complete.
 
 ```javascript
-sharp.embedWhite("input.jpg", "output.jpg", 200, 300, function(err) {
+sharp.embedWhite("input.jpg", "output.png", 200, 300, function(err) {
   if (err) {
     throw err;
   }
   // output.jpg is a 200 pixels wide and 300 pixels high image
-  // containing a scaled version of input.jpg embedded on a white canvas
+  // containing a scaled version of input.png embedded on a white canvas
 });
 ```
 
 ### embedBlack(inputPath, outputPath, width, height, callback)
 
-Scale and embed JPEG `inputPath` to `width` x `height` using a black canvas and write JPEG to `outputPath` calling `callback` when complete.
+Scale and embed `inputPath` to `width` x `height` using a black canvas and write to `outputPath` calling `callback` when complete.
 
 ```javascript
-sharp.embedBlack("input.jpg", "output.jpg", 200, 300, function(err) {
+sharp.embedBlack("input.png", "output.png", 200, 300, function(err) {
   if (err) {
     throw err;
   }
-  // output.jpg is a 200 pixels wide and 300 pixels high image
-  // containing a scaled version of input.jpg embedded on a black canvas
+  // output.png is a 200 pixels wide and 300 pixels high image
+  // containing a scaled version of input.png embedded on a black canvas
 });
 ```
 
@@ -89,29 +89,37 @@ sharp.embedBlack("input.jpg", "output.jpg", 200, 300, function(err) {
 
 ## Performance
 
-### AMD Athlon 4x core 3.3GHz 512KB L2
+Test environment:
 
-* imagemagick x 5.55 ops/sec ±0.45% (31 runs sampled)
-* gm x 10.31 ops/sec ±3.57% (53 runs sampled)
-* epeg x 27.79 ops/sec ±0.12% (69 runs sampled)
-* sharp x 31.52 ops/sec ±8.74% (80 runs sampled)
+* AMD Athlon 4 core 3.3GHz 512KB L2 CPU 1333 DDR3
+* libvips 7.36
+* libjpeg-turbo8 1.2.1
+* libpng 1.6.6
+* zlib1g 1.2.7
 
-### AWS t1.micro
+#### JPEG
 
-* imagemagick x 1.36 ops/sec ±0.96% (11 runs sampled)
-* sharp x 12.42 ops/sec ±5.84% (64 runs sampled)
+* imagemagick x 5.53 ops/sec ±0.55% (31 runs sampled)
+* gm x 10.86 ops/sec ±0.43% (56 runs sampled)
+* epeg x 28.07 ops/sec ±0.07% (70 runs sampled)
+* sharp x 31.60 ops/sec ±8.80% (80 runs sampled)
 
-### AWS m1.medium
+#### PNG
 
-* imagemagick x 1.38 ops/sec ±0.45% (11 runs sampled)
-* sharp x 12.66 ops/sec ±5.54% (65 runs sampled)
+* imagemagick x 4.65 ops/sec ±0.37% (27 runs sampled)
+* gm x 21.65 ops/sec ±0.18% (56 runs sampled)
+* sharp x 39.47 ops/sec ±6.78% (68 runs sampled)
 
-### AWS c1.medium
+## Licence
 
-* imagemagick x 2.10 ops/sec ±0.67% (15 runs sampled)
-* sharp x 18.97 ops/sec ±10.54% (52 runs sampled)
+Copyright 2013 Lovell Fuller
 
-### AWS m3.xlarge
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at [http://www.apache.org/licenses/LICENSE-2.0](http://www.apache.org/licenses/LICENSE-2.0.html)
 
-* imagemagick x 4.46 ops/sec ±0.33% (26 runs sampled)
-* sharp x 28.89 ops/sec ±7.75% (74 runs sampled)
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.