DeduceJpegColorSpace()

src/ImageSharp/Formats/Jpeg/Common/Decoder/IRawJpegData.cs

@@ -1,15 +1,32 @@
-namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
+using System.Collections.Generic;
-{
-    using System.Collections.Generic;
 
-    using SixLabors.Primitives;
+using SixLabors.Primitives;
 
+namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
+{
+    /// <summary>
+    /// Represents decompressed, unprocessed jpeg data with spectral space <see cref="IJpegComponent"/>-s.
+    /// </summary>
     internal interface IRawJpegData
     {
+        /// <summary>
+        /// Gets the image size in pixels.
+        /// </summary>
         Size ImageSizeInPixels { get; }
 
+        /// <summary>
+        /// Gets the number of coponents.
+        /// </summary>
         int ComponentCount { get; }
 
+        /// <summary>
+        /// Gets the color space
+        /// </summary>
+        JpegColorSpace ColorSpace { get; }
+
+        /// <summary>
+        /// Gets the components.
+        /// </summary>
         IEnumerable<IJpegComponent> Components { get; }
 
         /// <summary>

src/ImageSharp/Formats/Jpeg/Common/Decoder/JpegColorSpace.cs

@@ -0,0 +1,20 @@
+namespace SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder
+{
+    /// <summary>
+    /// Identifies the colorspace of a Jpeg image
+    /// </summary>
+    internal enum JpegColorSpace
+    {
+        Undefined = 0,
+
+        GrayScale,
+
+        Ycck,
+
+        Cmyk,
+
+        RGB,
+
+        YCbCr
+    }
+}

src/ImageSharp/Formats/Jpeg/GolangPort/OrigJpegDecoderCore.cs

@@ -4,14 +4,12 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
-using System.Linq;
-using System.Numerics;
 using System.Runtime.CompilerServices;
 using System.Threading.Tasks;
+
 using SixLabors.ImageSharp.Formats.Jpeg.Common;
 using SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder;
 using SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder;
-using SixLabors.ImageSharp.Memory;
 using SixLabors.ImageSharp.MetaData;
 using SixLabors.ImageSharp.MetaData.Profiles.Exif;
 using SixLabors.ImageSharp.MetaData.Profiles.Icc;
@@ -119,6 +117,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
         /// </summary>
         public SubsampleRatio SubsampleRatio { get; private set; }
 
+        public JpegColorSpace ColorSpace { get; private set; }
+
         /// <summary>
         /// Gets the component array
         /// </summary>
@@ -921,12 +921,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
             byte[] profile = new byte[remaining];
             this.InputProcessor.ReadFull(profile, 0, remaining);
 
-            if (profile[0] == 'E' &&
+            if (profile[0] == 'E' && profile[1] == 'x' && profile[2] == 'i' && profile[3] == 'f' && profile[4] == '\0'
-                profile[1] == 'x' &&
+                && profile[5] == '\0')
-                profile[2] == 'i' &&
-                profile[3] == 'f' &&
-                profile[4] == '\0' &&
-                profile[5] == '\0')
             {
                 this.isExif = true;
                 this.MetaData.ExifProfile = new ExifProfile(profile);
@@ -951,18 +947,9 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
             this.InputProcessor.ReadFull(identifier, 0, Icclength);
             remaining -= Icclength; // we have read it by this point
 
-            if (identifier[0] == 'I' &&
+            if (identifier[0] == 'I' && identifier[1] == 'C' && identifier[2] == 'C' && identifier[3] == '_'
-                identifier[1] == 'C' &&
+                && identifier[4] == 'P' && identifier[5] == 'R' && identifier[6] == 'O' && identifier[7] == 'F'
-                identifier[2] == 'C' &&
+                && identifier[8] == 'I' && identifier[9] == 'L' && identifier[10] == 'E' && identifier[11] == '\0')
-                identifier[3] == '_' &&
-                identifier[4] == 'P' &&
-                identifier[5] == 'R' &&
-                identifier[6] == 'O' &&
-                identifier[7] == 'F' &&
-                identifier[8] == 'I' &&
-                identifier[9] == 'L' &&
-                identifier[10] == 'E' &&
-                identifier[11] == '\0')
             {
                 byte[] profile = new byte[remaining];
                 this.InputProcessor.ReadFull(profile, 0, remaining);
@@ -999,11 +986,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
             remaining -= 13;
 
             // TODO: We should be using constants for this.
-            this.isJfif = this.Temp[0] == 'J' &&
+            this.isJfif = this.Temp[0] == 'J' && this.Temp[1] == 'F' && this.Temp[2] == 'I' && this.Temp[3] == 'F'
-                          this.Temp[1] == 'F' &&
+                          && this.Temp[4] == '\x00';
-                          this.Temp[2] == 'I' &&
-                          this.Temp[3] == 'F' &&
-                          this.Temp[4] == '\x00';
 
             if (this.isJfif)
             {
@@ -1204,7 +1188,43 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
                 component.InitializeDerivedData(this);
             }
 
+            this.ColorSpace = this.DeduceJpegColorSpace();
+
             this.SubsampleRatio = ComponentUtils.GetSubsampleRatio(this.Components);
         }
+
+        private JpegColorSpace DeduceJpegColorSpace()
+        {
+            switch (this.ComponentCount)
+            {
+                case 1: return JpegColorSpace.GrayScale;
+                case 3: return this.IsRGB() ? JpegColorSpace.RGB : JpegColorSpace.YCbCr;
+                case 4:
+
+                    if (!this.adobeTransformValid)
+                    {
+                        throw new ImageFormatException(
+                            "Unknown color model: 4-component JPEG doesn't have Adobe APP14 metadata");
+                    }
+
+                    // See http://www.sno.phy.queensu.ca/~phil/exiftool/TagNames/JPEG.html#Adobe
+                    // See https://docs.oracle.com/javase/8/docs/api/javax/imageio/metadata/doc-files/jpeg_metadata.html
+                    // TODO: YCbCrA?
+                    if (this.adobeTransform == OrigJpegConstants.Adobe.ColorTransformYcck)
+                    {
+                        return JpegColorSpace.Ycck;
+                    }
+                    else if (this.adobeTransform == OrigJpegConstants.Adobe.ColorTransformUnknown)
+                    {
+                        // Assume CMYK
+                        return JpegColorSpace.Cmyk;
+                    }
+
+                    goto default;
+
+                default:
+                    throw new ImageFormatException("JpegDecoder only supports RGB, CMYK and Grayscale color spaces.");
+            }
+        }
     }
 }

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

@@ -1,4 +1,7 @@
+using System;
+
 using SixLabors.ImageSharp.Formats.Jpeg.Common;
+using SixLabors.ImageSharp.Formats.Jpeg.Common.Decoder;
 using SixLabors.ImageSharp.Formats.Jpeg.GolangPort;
 using SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder;
 using SixLabors.ImageSharp.Tests.Formats.Jpg.Utils;
@@ -20,6 +23,21 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             this.Output = output;
         }
 
+        [Theory]
+        [InlineData(TestImages.Jpeg.Baseline.Testorig420, JpegColorSpace.YCbCr)]
+        [InlineData(TestImages.Jpeg.Baseline.Jpeg400, JpegColorSpace.GrayScale)]
+        [InlineData(TestImages.Jpeg.Baseline.Ycck, JpegColorSpace.Ycck)]
+        [InlineData(TestImages.Jpeg.Baseline.Cmyk, JpegColorSpace.Cmyk)]
+        public void ColorSpace_IsDeducedCorrectly(string imageFile, object expectedColorSpaceValue)
+        {
+            var expecteColorSpace = (JpegColorSpace)expectedColorSpaceValue;
+
+            using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(imageFile, true))
+            {
+                Assert.Equal(expecteColorSpace, decoder.ColorSpace);
+            }
+        }
+
         [Fact]
         public void ComponentScalingIsCorrect_1ChannelJpeg()
         {