Fix decoding of JPX images having an alpha channel

When an image has a non-zero SMaskInData it means that the image
has an alpha channel.
With JPX images, the colorspace isn't required (by spec) so when we
don't have it, the JPX decoder will handle the conversion in RGBA
format.

src/core/base_stream.js

@@ -49,8 +49,8 @@ class BaseStream {
    *       to be fully loaded, since otherwise intermittent errors may occur;
    *       note the `ObjectLoader` class.
    */
-  async getImageData(length, ignoreColorSpace) {
-    return this.getBytes(length, ignoreColorSpace);
+  async getImageData(length, decoderOptions) {
+    return this.getBytes(length, decoderOptions);
   }
 
   async asyncGetBytes() {

src/core/colorspace.js

@@ -370,6 +370,8 @@ class ColorSpace {
         case "RGB":
         case "DeviceRGB":
           return this.singletons.rgb;
+        case "DeviceRGBA":
+          return this.singletons.rgba;
         case "CMYK":
         case "DeviceCMYK":
           return this.singletons.cmyk;
@@ -511,6 +513,9 @@ class ColorSpace {
       get rgb() {
         return shadow(this, "rgb", new DeviceRgbCS());
       },
+      get rgba() {
+        return shadow(this, "rgba", new DeviceRgbaCS());
+      },
       get cmyk() {
         return shadow(this, "cmyk", new DeviceCmykCS());
       },
@@ -778,6 +783,23 @@ class DeviceRgbCS extends ColorSpace {
   }
 }
 
+/**
+ * The default color is `new Float32Array([0, 0, 0, 1])`.
+ */
+class DeviceRgbaCS extends ColorSpace {
+  constructor() {
+    super("DeviceRGBA", 4);
+  }
+
+  getOutputLength(inputLength, _alpha01) {
+    return inputLength * 4;
+  }
+
+  isPassthrough(bits) {
+    return bits === 8;
+  }
+}
+
 /**
  * The default color is `new Float32Array([0, 0, 0, 1])`.
  */

src/core/decode_stream.js

@@ -73,7 +73,7 @@ class DecodeStream extends BaseStream {
     return this.buffer[this.pos++];
   }
 
-  getBytes(length, ignoreColorSpace = false) {
+  getBytes(length, decoderOptions = null) {
     const pos = this.pos;
     let end;
 
@@ -82,7 +82,7 @@ class DecodeStream extends BaseStream {
       end = pos + length;
 
       while (!this.eof && this.bufferLength < end) {
-        this.readBlock(ignoreColorSpace);
+        this.readBlock(decoderOptions);
       }
       const bufEnd = this.bufferLength;
       if (end > bufEnd) {
@@ -90,7 +90,7 @@ class DecodeStream extends BaseStream {
       }
     } else {
       while (!this.eof) {
-        this.readBlock(ignoreColorSpace);
+        this.readBlock(decoderOptions);
       }
       end = this.bufferLength;
     }
@@ -99,12 +99,12 @@ class DecodeStream extends BaseStream {
     return this.buffer.subarray(pos, end);
   }
 
-  async getImageData(length, ignoreColorSpace = false) {
+  async getImageData(length, decoderOptions = null) {
     if (!this.canAsyncDecodeImageFromBuffer) {
-      return this.getBytes(length, ignoreColorSpace);
+      return this.getBytes(length, decoderOptions);
     }
     const data = await this.stream.asyncGetBytes();
-    return this.decodeImage(data, ignoreColorSpace);
+    return this.decodeImage(data, decoderOptions);
   }
 
   reset() {

src/core/flate_stream.js

@@ -149,7 +149,7 @@ class FlateStream extends DecodeStream {
     this.codeBuf = 0;
   }
 
-  async getImageData(length, _ignoreColorSpace) {
+  async getImageData(length, _decoderOptions) {
     const data = await this.asyncGetBytes();
     return data?.subarray(0, length) || this.getBytes(length);
   }

src/core/image.js

@@ -18,7 +18,6 @@ import {
   FeatureTest,
   FormatError,
   ImageKind,
-  info,
   warn,
 } from "../shared/util.js";
 import {
@@ -104,7 +103,6 @@ class PDFImage {
     localColorSpaceCache,
   }) {
     this.image = image;
-    let jpxDecode = false;
     const dict = image.dict;
 
     const filter = dict.get("F", "Filter");
@@ -126,7 +124,11 @@ class PDFImage {
           bitsPerComponent: image.bitsPerComponent,
         } = JpxImage.parseImageProperties(image.stream));
         image.stream.reset();
-        jpxDecode = true;
+        this.jpxDecoderOptions = {
+          numComponents: 0,
+          isIndexedColormap: false,
+          smaskInData: dict.has("SMaskInData"),
+        };
         break;
       case "JBIG2Decode":
         image.bitsPerComponent = 1;
@@ -180,23 +182,31 @@ class PDFImage {
 
     if (!this.imageMask) {
       let colorSpace = dict.getRaw("CS") || dict.getRaw("ColorSpace");
-      if (!colorSpace) {
-        info("JPX images (which do not require color spaces)");
-        switch (image.numComps) {
-          case 1:
-            colorSpace = Name.get("DeviceGray");
-            break;
-          case 3:
-            colorSpace = Name.get("DeviceRGB");
-            break;
-          case 4:
-            colorSpace = Name.get("DeviceCMYK");
-            break;
-          default:
-            throw new Error(
-              `JPX images with ${image.numComps} color components not supported.`
-            );
+      const hasColorSpace = !!colorSpace;
+      if (!hasColorSpace) {
+        if (this.jpxDecoderOptions) {
+          colorSpace = Name.get("DeviceRGBA");
+        } else {
+          switch (image.numComps) {
+            case 1:
+              colorSpace = Name.get("DeviceGray");
+              break;
+            case 3:
+              colorSpace = Name.get("DeviceRGB");
+              break;
+            case 4:
+              colorSpace = Name.get("DeviceCMYK");
+              break;
+            default:
+              throw new Error(
+                `Images with ${image.numComps} color components not supported.`
+              );
+          }
         }
+      } else if (this.jpxDecoderOptions?.smaskInData) {
+        // If the jpx image has a color space then it mustn't be used in order
+        // to be able to use the color space that comes from the pdf.
+        colorSpace = Name.get("DeviceRGBA");
       }
 
       this.colorSpace = ColorSpace.parse({
@@ -208,9 +218,13 @@ class PDFImage {
       });
       this.numComps = this.colorSpace.numComps;
 
-      // If the jpx image has a color space then it musn't be used in order to
-      // be able to use the color space that comes from the pdf.
-      this.ignoreColorSpace = jpxDecode && this.colorSpace.name === "Indexed";
+      if (this.jpxDecoderOptions) {
+        this.jpxDecoderOptions.numComponents = hasColorSpace ? this.numComp : 0;
+        // If the jpx image has a color space then it musn't be used in order to
+        // be able to use the color space that comes from the pdf.
+        this.jpxDecoderOptions.isIndexedColormap =
+          this.colorSpace.name === "Indexed";
+      }
     }
 
     this.decode = dict.getArray("D", "Decode");
@@ -691,6 +705,28 @@ class PDFImage {
       isOffscreenCanvasSupported &&
       ImageResizer.needsToBeResized(drawWidth, drawHeight);
 
+    if (this.colorSpace.name === "DeviceRGBA") {
+      imgData.kind = ImageKind.RGBA_32BPP;
+      const imgArray = (imgData.data = await this.getImageBytes(
+        originalHeight * originalWidth * 4,
+        {}
+      ));
+
+      if (isOffscreenCanvasSupported) {
+        if (!mustBeResized) {
+          return this.createBitmap(
+            ImageKind.RGBA_32BPP,
+            drawWidth,
+            drawHeight,
+            imgArray
+          );
+        }
+        return ImageResizer.createImage(imgData, false);
+      }
+
+      return imgData;
+    }
+
     if (!forceRGBA) {
       // If it is a 1-bit-per-pixel grayscale (i.e. black-and-white) image
       // without any complications, we pass a same-sized copy to the main
@@ -994,7 +1030,7 @@ class PDFImage {
     this.image.forceRGB = !!forceRGB;
     const imageBytes = await this.image.getImageData(
       length,
-      this.ignoreColorSpace
+      this.jpxDecoderOptions
     );
 
     // If imageBytes came from a DecodeStream, we're safe to transfer it

src/core/jpx.js

@@ -26,9 +26,10 @@ class JpxError extends BaseException {
 class JpxImage {
   static #module = null;
 
-  static decode(data, ignoreColorSpace = false) {
+  static decode(data, decoderOptions) {
+    decoderOptions ||= {};
     this.#module ||= OpenJPEG({ warn });
-    const imageData = this.#module.decode(data, ignoreColorSpace);
+    const imageData = this.#module.decode(data, decoderOptions);
     if (typeof imageData === "string") {
       throw new JpxError(imageData);
     }

src/core/jpx_stream.js

@@ -41,16 +41,16 @@ class JpxStream extends DecodeStream {
     // directly insert all of its data into `this.buffer`.
   }
 
-  readBlock(ignoreColorSpace) {
-    this.decodeImage(null, ignoreColorSpace);
+  readBlock(decoderOptions) {
+    this.decodeImage(null, decoderOptions);
   }
 
-  decodeImage(bytes, ignoreColorSpace) {
+  decodeImage(bytes, decoderOptions) {
     if (this.eof) {
       return this.buffer;
     }
     bytes ||= this.bytes;
-    this.buffer = JpxImage.decode(bytes, ignoreColorSpace);
+    this.buffer = JpxImage.decode(bytes, decoderOptions);
     this.bufferLength = this.buffer.length;
     this.eof = true;