Adding support for grayscale JPEG.

examples/grayscale-image.js

@@ -0,0 +1,22 @@
+/**
+ * Passing grayscale image through canvas.  Image should remain a gray square.
+ * If image is distorted with lines, then grayscale images are being distorted.
+ */
+var Canvas = require('../lib/canvas')
+  , Image = Canvas.Image
+  , canvas = new Canvas(288, 288)
+  , ctx = canvas.getContext('2d')
+  , fs = require('fs');
+
+var grayScaleImage = fs.readFileSync(__dirname + '/images/grayscaleImage.jpg');
+img = new Image;
+img.src = grayScaleImage;
+
+ctx.drawImage(img, 0, 0);
+
+var out = fs.createWriteStream(__dirname + '/passedThroughGrayscale.jpg')
+  , stream = canvas.createJPEGStream();
+
+stream.on('data', function(chunk){
+  out.write(chunk);
+});

src/Image.cc

@@ -692,12 +692,20 @@ Image::decodeJPEGIntoSurface(jpeg_decompress_struct *info) {
     jpeg_read_scanlines(info, &src, 1);
     uint32_t *row = (uint32_t *)(data + stride * y);
     for (int x = 0; x < width; ++x) {
-      int bx = 3 * x;
+      if (info->jpeg_color_space == 1) {
-      uint32_t *pixel = row + x;
+        uint32_t *pixel = row + x;
-      *pixel = 255 << 24
+        *pixel = 255 << 24
-        | src[bx + 0] << 16
+          | src[x] << 16
-        | src[bx + 1] << 8
+          | src[x] << 8
-        | src[bx + 2];
+          | src[x];
+      } else {
+        int bx = 3 * x;
+        uint32_t *pixel = row + x;
+        *pixel = 255 << 24
+          | src[bx + 0] << 16
+          | src[bx + 1] << 8
+          | src[bx + 2];	
+      }
     }
   }