Use sync version of zlib deflate method to compress png images

demo/png-benchmark.js

@@ -0,0 +1,33 @@
+const PDFDocument = require('../');
+const fs = require('fs');
+
+const doc = new PDFDocument();
+
+// files with alpha channel -> uses zlib.deflate
+const files = [  
+  'test.png',
+  'test3.png'
+];
+
+const filesData = files.map(fileName => {
+  return fs.readFileSync(`images/${fileName}`);
+});
+
+const iterationCount = 100;
+
+console.time('png-bench')
+
+for (let i = 0; i < iterationCount; i++) {  
+  filesData.forEach(data => {
+    doc.image(data)
+    doc.addPage()
+  })
+}
+
+doc.on('data', () => {})
+
+doc.on('end', () => {  
+  console.timeEnd('png-bench');
+});
+
+doc.end();

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();
     });
   }
 }

tests/unit/png.spec.js

@@ -0,0 +1,170 @@
+const PDFDocument = require("../../lib/document").default;
+const PDFReference = require("../../lib/reference").default;
+const PNGImage = require("../../lib/image/png").default;
+const fs = require("fs");
+
+describe("PNGImage", () => {
+  let document;
+
+  const createImage = fileName => {
+    const img = new PNGImage(fs.readFileSync(fileName), "I1");
+    // noop data manipulation methods
+    img.loadIndexedAlphaChannel = () => {
+      if (img.image.hasAlphaChannel) {
+        img.alphaChannel = {};
+      }
+    };
+    img.splitAlphaChannel = () => {
+      if (img.image.hasAlphaChannel) {
+        img.alphaChannel = {};
+      }
+    };
+    img.embed(document);
+    img.finalize();
+    return img;
+  };
+
+  beforeEach(() => {
+    document = new PDFDocument();
+  });
+
+  test("RGB", () => {
+    // ImageWidth = 400
+    // ImageHeight = 533
+    // BitDepth = 8
+    // ColorType = 2 (RGB)
+    // Compression = 0
+    // Filter = 0
+    // Interlace = 0
+
+    const img = createImage("./demo/images/test2.png");
+
+    expect(img.obj.data).toMatchObject({
+      BitsPerComponent: 8,
+      ColorSpace: "DeviceRGB",
+      Filter: "FlateDecode",
+      Height: 533,
+      Length: 397011,
+      Subtype: "Image",
+      Type: "XObject",
+      Width: 400,
+      DecodeParms: expect.any(PDFReference)
+    });
+
+    expect(img.obj.data.DecodeParms.data).toMatchObject({
+      BitsPerComponent: 8,
+      Colors: 3,
+      Columns: 400,
+      Predictor: 15
+    });
+  });
+
+  test("RGB with Alpha", () => {
+    // ImageWidth = 409
+    // ImageHeight = 400
+    // BitDepth = 8
+    // ColorType = 6 (RGB with Alpha)
+    // Compression = 0
+    // Filter = 0
+    // Interlace = 0
+
+    const img = createImage("./tests/images/bee.png");
+
+    expect(img.obj.data).toMatchObject({
+      BitsPerComponent: 8,
+      ColorSpace: "DeviceRGB",
+      Filter: "FlateDecode",
+      Height: 400,
+      Length: 47715,
+      Subtype: "Image",
+      Type: "XObject",
+      Width: 409,
+      SMask: expect.any(PDFReference)
+    });
+
+    expect(img.obj.data.SMask.data).toMatchObject({
+      BitsPerComponent: 8,
+      ColorSpace: "DeviceGray",
+      Decode: [
+        0,
+        1
+      ],
+      Filter: "FlateDecode",
+      Height: 400,
+      Length: 16,
+      Subtype: "Image",
+      Type: "XObject",
+      Width: 409,
+    });
+  });
+
+  test("Pallete", () => {
+    // ImageWidth = 980
+    // ImageHeight = 540
+    // BitDepth = 8
+    // ColorType = 3 (Pallete)
+    // Compression = 0
+    // Filter = 0
+    // Interlace = 0
+
+    const img = createImage("./demo/images/test3.png");
+
+    expect(img.obj.data).toMatchObject({
+      BitsPerComponent: 8,
+      ColorSpace: ["Indexed", "DeviceRGB", 255, expect.any(PDFReference)],
+      Filter: "FlateDecode",
+      Height: 540,
+      Length: 56682,
+      Subtype: "Image",
+      Type: "XObject",
+      Width: 980,
+      DecodeParms: expect.any(PDFReference)
+    });
+
+    expect(img.obj.data.DecodeParms.data).toMatchObject({
+      BitsPerComponent: 8,
+      Colors: 1,
+      Columns: 980,
+      Predictor: 15
+    });
+  });
+
+  test("Grayscale with Alpha", () => {
+    // ImageWidth = 112
+    // ImageHeight = 112
+    // BitDepth = 8
+    // ColorType = 4 (Grayscale with Alpha)
+    // Compression = 0
+    // Filter = 0
+    // Interlace = 0
+
+    const img = createImage("./tests/images/fish.png");
+
+    expect(img.obj.data).toMatchObject({
+      BitsPerComponent: 8,
+      ColorSpace: "DeviceGray",
+      Filter: "FlateDecode",
+      Height: 112,
+      Length: 9922,
+      Subtype: "Image",
+      Type: "XObject",
+      Width: 112,
+      SMask: expect.any(PDFReference)
+    });
+
+    expect(img.obj.data.SMask.data).toMatchObject({
+      BitsPerComponent: 8,
+      ColorSpace: "DeviceGray",
+      Decode: [
+        0,
+        1
+      ],
+      Filter: "FlateDecode",
+      Height: 112,
+      Length: 16,
+      Subtype: "Image",
+      Type: "XObject",
+      Width: 112,
+    });
+  });
+});