Fix embedded CMYK image (#415)

* Fix embedded CMYK image rendering blank

* Fix embedded CMYK image rendering inverted

* Add test for CMYK embedding

src/core/embedders/JpegEmbedder.ts

@@ -13,19 +13,19 @@ const MARKERS = [
 enum ColorSpace {
   DeviceGray = 'DeviceGray',
   DeviceRGB = 'DeviceRGB',
-  DeviceCYMK = 'DeviceCYMK',
+  DeviceCMYK = 'DeviceCMYK',
 }
 
 const ChannelToColorSpace: { [idx: number]: ColorSpace | undefined } = {
   1: ColorSpace.DeviceGray,
   3: ColorSpace.DeviceRGB,
-  4: ColorSpace.DeviceCYMK,
+  4: ColorSpace.DeviceCMYK,
 };
 
 /**
  * A note of thanks to the developers of https://github.com/foliojs/pdfkit, as
  * this class borrows from:
- *   https://github.com/devongovett/pdfkit/blob/e71edab0dd4657b5a767804ba86c94c58d01fbca/lib/image/jpeg.coffee
+ *   https://github.com/foliojs/pdfkit/blob/a6af76467ce06bd6a2af4aa7271ccac9ff152a7d/lib/image/jpeg.js
  */
 class JpegEmbedder {
   static async for(imageData: Uint8Array) {
@@ -100,6 +100,24 @@ class JpegEmbedder {
       Height: this.height,
       ColorSpace: this.colorSpace,
       Filter: 'DCTDecode',
+      // CMYK JPEG streams in PDF are typically stored complemented,
+      // with 1 as 'off' and 0 as 'on' (PDF 32000-1:2008, 8.6.4.4).
+      // 
+      // Standalone CMYK JPEG (usually exported by Photoshop) are
+      // stored inverse, with 0 as 'off' and 1 as 'on', like RGB.
+      //
+      // Applying a swap here as a hedge that most bytes passing
+      // through this method will benefit from it.
+      Decode: this.colorSpace === ColorSpace.DeviceCMYK && [
+        1,
+        0,
+        1,
+        0,
+        1,
+        0,
+        1,
+        0,
+      ],
     });
 
     if (ref) {

tests/core/embedders/JpegEmbedder.spec.ts

@@ -3,6 +3,7 @@ import { JpegEmbedder, PDFContext, PDFRawStream, PDFRef } from 'src/core';
 
 const catUnicornJpg = fs.readFileSync('./assets/images/cat_riding_unicorn.jpg');
 const minionsLaughing = fs.readFileSync('./assets/images/minions_laughing.jpg');
+const cmykJpg = fs.readFileSync('./assets/images/Channel_digital_image_CMYK_color.jpg');
 
 describe(`JpegEmbedder`, () => {
   it(`can be constructed with JpegEmbedder.for(...)`, async () => {
@@ -49,4 +50,13 @@ describe(`JpegEmbedder`, () => {
     expect(embedder.width).toBe(630);
     expect(embedder.colorSpace).toBe('DeviceRGB');
   });
+
+  it(`can extract properties of JPEG images (3)`, async () => {
+    const embedder = await JpegEmbedder.for(cmykJpg);
+
+    expect(embedder.bitsPerComponent).toBe(8);
+    expect(embedder.height).toBe(333);
+    expect(embedder.width).toBe(500);
+    expect(embedder.colorSpace).toBe('DeviceCMYK');
+  });
 });