Merge pull request #1732 from SixLabors/bp/deduceColorSpaceFix

If component id's are R, G, B in ASCII the color space should be RGB

Author: brianpopow

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -345,10 +345,10 @@ public void Dispose()
         }
 
         /// <summary>
-        /// Returns the correct colorspace based on the image component count
+        /// Returns the correct colorspace based on the image component count and the jpeg frame components.
         /// </summary>
         /// <returns>The <see cref="JpegColorSpace"/></returns>
-        private JpegColorSpace DeduceJpegColorSpace(byte componentCount)
+        private JpegColorSpace DeduceJpegColorSpace(byte componentCount, JpegComponent[] components)
         {
             if (componentCount == 1)
             {
@@ -362,6 +362,12 @@ private JpegColorSpace DeduceJpegColorSpace(byte componentCount)
                     return JpegColorSpace.RGB;
                 }
 
+                // If the component Id's are R, G, B in ASCII the colorspace is RGB and not YCbCr.
+                if (components[2].Id == 66 && components[1].Id == 71 && components[0].Id == 82)
+                {
+                    return JpegColorSpace.RGB;
+                }
+
                 // Some images are poorly encoded and contain incorrect colorspace transform metadata.
                 // We ignore that and always fall back to the default colorspace.
                 return JpegColorSpace.YCbCr;
@@ -836,60 +842,60 @@ private void ProcessStartOfFrameMarker(BufferedReadStream stream, int remaining,
 
             // 1 byte: Number of components
             byte componentCount = this.temp[5];
-            this.ColorSpace = this.DeduceJpegColorSpace(componentCount);
-
-            this.Metadata.GetJpegMetadata().ColorType = this.ColorSpace == JpegColorSpace.Grayscale ? JpegColorType.Luminance : JpegColorType.YCbCr;
 
             this.Frame = new JpegFrame(frameMarker, precision, frameWidth, frameHeight, componentCount);
 
-            if (!metadataOnly)
+            remaining -= length;
+
+            // Validate: remaining part must be equal to components * 3
+            const int componentBytes = 3;
+            if (remaining != componentCount * componentBytes)
             {
-                remaining -= length;
+                JpegThrowHelper.ThrowBadMarker("SOFn", remaining);
+            }
 
-                // Validate: remaining part must be equal to components * 3
-                const int componentBytes = 3;
-                if (remaining != componentCount * componentBytes)
-                {
-                    JpegThrowHelper.ThrowBadMarker("SOFn", remaining);
-                }
+            // components*3 bytes: component data
+            stream.Read(this.temp, 0, remaining);
+
+            // No need to pool this. They max out at 4
+            this.Frame.ComponentIds = new byte[componentCount];
+            this.Frame.ComponentOrder = new byte[componentCount];
+            this.Frame.Components = new JpegComponent[componentCount];
 
-                // components*3 bytes: component data
-                stream.Read(this.temp, 0, remaining);
+            int maxH = 0;
+            int maxV = 0;
+            int index = 0;
+            for (int i = 0; i < componentCount; i++)
+            {
+                byte hv = this.temp[index + 1];
+                int h = (hv >> 4) & 15;
+                int v = hv & 15;
 
-                // No need to pool this. They max out at 4
-                this.Frame.ComponentIds = new byte[componentCount];
-                this.Frame.ComponentOrder = new byte[componentCount];
-                this.Frame.Components = new JpegComponent[componentCount];
+                if (maxH < h)
+                {
+                    maxH = h;
+                }
 
-                int maxH = 0;
-                int maxV = 0;
-                int index = 0;
-                for (int i = 0; i < componentCount; i++)
+                if (maxV < v)
                 {
-                    byte hv = this.temp[index + 1];
-                    int h = (hv >> 4) & 15;
-                    int v = hv & 15;
+                    maxV = v;
+                }
 
-                    if (maxH < h)
-                    {
-                        maxH = h;
-                    }
+                var component = new JpegComponent(this.Configuration.MemoryAllocator, this.Frame, this.temp[index], h, v, this.temp[index + 2], i);
 
-                    if (maxV < v)
-                    {
-                        maxV = v;
-                    }
+                this.Frame.Components[i] = component;
+                this.Frame.ComponentIds[i] = component.Id;
 
-                    var component = new JpegComponent(this.Configuration.MemoryAllocator, this.Frame, this.temp[index], h, v, this.temp[index + 2], i);
+                index += componentBytes;
+            }
 
-                    this.Frame.Components[i] = component;
-                    this.Frame.ComponentIds[i] = component.Id;
+            this.ColorSpace = this.DeduceJpegColorSpace(componentCount, this.Frame.Components);
 
-                    index += componentBytes;
-                }
+            this.Metadata.GetJpegMetadata().ColorType = this.ColorSpace == JpegColorSpace.Grayscale ? JpegColorType.Luminance : JpegColorType.YCbCr;
 
+            if (!metadataOnly)
+            {
                 this.Frame.Init(maxH, maxV);
-
                 this.scanDecoder.InjectFrameData(this.Frame, this);
             }
         }

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.cs

@@ -174,6 +174,19 @@ public async Task Identify_IsCancellable()
             await Assert.ThrowsAsync<TaskCanceledException>(async () => await Image.IdentifyAsync(config, "someFakeFile", cts.Token));
         }
 
+        // https://github.com/SixLabors/ImageSharp/pull/1732
+        [Theory]
+        [WithFile(TestImages.Jpeg.Issues.WrongColorSpace, PixelTypes.Rgba32)]
+        public void Issue1732_DecodesWithRgbColorSpace<TPixel>(TestImageProvider<TPixel> provider)
+            where TPixel : unmanaged, IPixel<TPixel>
+        {
+            using (Image<TPixel> image = provider.GetImage(new JpegDecoder()))
+            {
+                image.DebugSave(provider);
+                image.CompareToOriginal(provider);
+            }
+        }
+
         // DEBUG ONLY!
         // The PDF.js output should be saved by "tests\ImageSharp.Tests\Formats\Jpg\pdfjs\jpeg-converter.htm"
         // into "\tests\Images\ActualOutput\JpegDecoderTests\"

tests/ImageSharp.Tests/TestImages.cs

@@ -237,6 +237,7 @@ public static class Issues
                 public const string ExifResize1049 = "Jpg/issues/issue1049-exif-resize.jpg";
                 public const string BadSubSampling1076 = "Jpg/issues/issue-1076-invalid-subsampling.jpg";
                 public const string IdentifyMultiFrame1211 = "Jpg/issues/issue-1221-identify-multi-frame.jpg";
+                public const string WrongColorSpace = "Jpg/issues/Issue1732-WrongColorSpace.jpg";
 
                 public static class Fuzz
                 {