Use sync version of zlib deflate method to compress png images

Author: blikblum

lib/image/png.js

@@ -114,7 +114,7 @@ class PNGImage {
       const imgData = new Buffer(pixelCount * colorByteSize);
       const alphaChannel = new Buffer(pixelCount);
 
-      let i = (p = (a = 0));
+      let i = p = a = 0;
       const len = pixels.length;
       while (i < len) {
         imgData[p++] = pixels[i++];
@@ -123,22 +123,13 @@ class PNGImage {
         alphaChannel[a++] = pixels[i++];
       }
 
-      let done = 0;
-      zlib.deflate(imgData, (err, imgData1) => {
-        this.imgData = imgData1;
-        if (err) { throw err; }
-        if (++done === 2) { return this.finalize(); }
-      });
-
-      return zlib.deflate(alphaChannel, (err, alphaChannel1) => {
-        this.alphaChannel = alphaChannel1;
-        if (err) { throw err; }
-        if (++done === 2) { return this.finalize(); }
-      });
+      this.imgData = zlib.deflateSync(imgData);
+      this.alphaChannel = zlib.deflateSync(alphaChannel);
+      return this.finalize();
     });
   }
 
-  loadIndexedAlphaChannel(fn) {
+  loadIndexedAlphaChannel() {
     const transparency = this.image.transparency.indexed;
     return this.image.decodePixels(pixels => {
       const alphaChannel = new Buffer(this.width * this.height);
@@ -148,11 +139,8 @@ class PNGImage {
         alphaChannel[i++] = transparency[pixels[j]];
       }
 
-      return zlib.deflate(alphaChannel, (err, alphaChannel1) => {
-        this.alphaChannel = alphaChannel1;
-        if (err) { throw err; }
-        return this.finalize();
-      });
+      this.alphaChannel = zlib.deflateSync(alphaChannel);
+      return this.finalize();
     });
   }
 }