Added support for encoding 8-bit grayscale images (colorType = 0 and 4) (#76)

* Added support for encoding 8-bit grayscale images (colorType = 4)

* Fixed unit tests, updated README

* [README.md] Added Browserify and TOC

README.md

@@ -11,15 +11,25 @@ Based on the original [pngjs](https://github.com/niegowski/node-pngjs) with the
   * Support for reading 1,2,4 & 16 bit files
   * Support for reading interlace files
   * Support for reading `tTRNS` transparent colours
-  * Support for writing colortype 2 (RGB) and colortype 6 (RGBA)
+  * Support for writing colortype 0 (grayscale), colortype 2 (RGB), colortype 4 (grayscale alpha) and colortype 6 (RGBA)
   * Sync interface as well as async
   * API compatible with pngjs and node-pngjs
 
 Known lack of support for:
 
   * Extended PNG e.g. Animation
-  * Writing in different formats, colortype 0 (greyscale), colortype 3 (indexed color), colortype 4 (greyscale with alpha)
-  * Synchronous write
+  * Writing in colortype 3 (indexed color)
+  
+# Table of Contents
+* [Requirements](#requirements)
+* [Comparison Table](#comparison-table)
+* [Tests](#tests)
+* [Installation](#installation)
+* [Browserify](#browserify)
+* [Example](#example)
+* [Async API](#async-api)
+* [Sync API](#sync-api)
+* [Changelog](#changelog)
 
 Requirements
 ============
@@ -63,6 +73,14 @@ Installation
 $ npm install pngjs  --save
 ```
 
+Browserify
+===========
+Use [Browserify](browserify.org) to build a version of library that can run client-side:
+```
+$ browserify lib/png.js --standalone png > bundle.js
+```
+Then depending on your module system you can either `require('bundle.js')` or if you're not using module loader you can use plain old `<script src="bundle.js"></script>` tag and the library will be available under `window.PNG` or just `PNG`.
+
 Example
 ==========
 ```js
@@ -112,7 +130,7 @@ As input any color type is accepted (grayscale, rgb, palette, grayscale with alp
 - `deflateStrategy` - compression strategy for delate (default: 3)
 - `deflateFactory` - deflate stream factory (default: `zlib.createDeflate`)
 - `filterType` - png filtering method for scanlines (default: -1 => auto, accepts array of numbers 0-4)
-- `colorType` - the output colorType - see constants. 2 = color, no alpha, 6 = color & alpha. Default currently 6, but in the future may calculate best mode.
+- `colorType` - the output colorType - see constants. 0 = grayscale, no alpha, 2 = color, no alpha, 4 = grayscale & alpha, 6 = color & alpha. Default currently 6, but in the future may calculate best mode.
 - `inputHasAlpha` - whether the input bitmap has 4 bits per pixel (rgb and alpha) or 3 (rgb - no alpha).
 - `bgColor` - an object containing red, green, and blue values between 0 and 255
 that is used when packing a PNG if alpha is not to be included (default: 255,255,255)
@@ -251,7 +269,8 @@ Take a PNG image and returns a buffer. The properties on the image include the m
 ```
 var data = fs.readFileSync('in.png');
 var png = PNG.sync.read(data);
-var buffer = PNG.sync.write(png);
+var options = { colorType: 6 };
+var buffer = PNG.sync.write(png, options);
 fs.writeFileSync('out.png', buffer);
 ```
 

lib/bitpacker.js

@@ -3,15 +3,19 @@
 var constants = require('./constants');
 
 module.exports = function(data, width, height, options) {
-  var outHasAlpha = options.colorType === constants.COLORTYPE_COLOR_ALPHA;
-  if (options.inputHasAlpha && outHasAlpha) {
-    return data;
-  }
-  if (!options.inputHasAlpha && !outHasAlpha) {
-    return data;
+  var outHasAlpha = [constants.COLORTYPE_COLOR_ALPHA, constants.COLORTYPE_ALPHA].indexOf(options.colorType) !== -1;
+
+  if ([constants.COLORTYPE_GRAYSCALE, constants.COLORTYPE_ALPHA].indexOf(options.colorType) === -1) {
+    // If no need to convert to grayscale and alpha is present/absent in both, take a fast route
+    if (options.inputHasAlpha && outHasAlpha) {
+      return data;
+    }
+    if (!options.inputHasAlpha && !outHasAlpha) {
+      return data;
+    }
   }
 
-  var outBpp = outHasAlpha ? 4 : 3;
+  var outBpp = constants.COLORTYPE_TO_BPP_MAP[options.colorType];
   var outData = new Buffer(width * height * outBpp);
   var inBpp = options.inputHasAlpha ? 4 : 3;
   var inIndex = 0;
@@ -48,11 +52,25 @@ module.exports = function(data, width, height, options) {
         alpha = 255;
       }
 
-      outData[outIndex] = red;
-      outData[outIndex + 1] = green;
-      outData[outIndex + 2] = blue;
-      if (outHasAlpha) {
-        outData[outIndex + 3] = alpha;
+      switch (options.colorType) {
+        case constants.COLORTYPE_COLOR_ALPHA:
+        case constants.COLORTYPE_COLOR:
+          outData[outIndex] = red;
+          outData[outIndex + 1] = green;
+          outData[outIndex + 2] = blue;
+          if (outHasAlpha) {
+            outData[outIndex + 3] = alpha;
+          }
+          break;
+        case constants.COLORTYPE_ALPHA:
+        case constants.COLORTYPE_GRAYSCALE:
+          // Convert to grayscale and alpha
+          var grayscale = (red + green + blue) / 3;
+          outData[outIndex] = grayscale;
+          if (outHasAlpha) {
+            outData[outIndex + 1] = alpha;
+          }
+          break;
       }
 
       inIndex += inBpp;

lib/packer.js

@@ -15,9 +15,16 @@ var Packer = module.exports = function(options) {
   options.inputHasAlpha = options.inputHasAlpha != null ? options.inputHasAlpha : true;
   options.deflateFactory = options.deflateFactory || zlib.createDeflate;
   options.bitDepth = options.bitDepth || 8;
+  // This is outputColorType
   options.colorType = (typeof options.colorType === 'number') ? options.colorType : constants.COLORTYPE_COLOR_ALPHA;
+  options.inputColorType = options.inputColorType || constants.COLORTYPE_COLOR_ALPHA;
 
-  if (options.colorType !== constants.COLORTYPE_COLOR && options.colorType !== constants.COLORTYPE_COLOR_ALPHA) {
+  if ([
+    constants.COLORTYPE_GRAYSCALE,
+    constants.COLORTYPE_COLOR,
+    constants.COLORTYPE_COLOR_ALPHA,
+    constants.COLORTYPE_ALPHA
+  ].indexOf(options.colorType) === -1) {
     throw new Error('option color type:' + options.colorType + ' is not supported at present');
   }
   if (options.bitDepth !== 8) {
@@ -74,7 +81,7 @@ Packer.prototype.packIHDR = function(width, height) {
   var buf = new Buffer(13);
   buf.writeUInt32BE(width, 0);
   buf.writeUInt32BE(height, 4);
-  buf[8] = this._options.bitDepth;  // Bit depth
+  buf[8] = this._options.bitDepth; // Bit depth
   buf[9] = this._options.colorType; // colorType
   buf[10] = 0; // compression
   buf[11] = 0; // filter
@@ -89,4 +96,4 @@ Packer.prototype.packIDAT = function(data) {
 
 Packer.prototype.packIEND = function() {
   return this._packChunk(constants.TYPE_IEND, null);
-};
+};

lib/png-sync.js

@@ -10,7 +10,7 @@ exports.read = function(buffer, options) {
   return parse(buffer, options || {});
 };
 
-exports.write = function(png) {
+exports.write = function(png, options) {
 
-  return pack(png);
+  return pack(png, options);
 };