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[0].Id == 82 && components[1].Id == 71 && components[2].Id == 66)
+                {
+                    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;
@@ -836,9 +842,6 @@ 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);
 
@@ -888,6 +891,9 @@ private void ProcessStartOfFrameMarker(BufferedReadStream stream, int remaining,
                     index += componentBytes;
                 }
 
+                this.ColorSpace = this.DeduceJpegColorSpace(componentCount, this.Frame.Components);
+                this.Metadata.GetJpegMetadata().ColorType = this.ColorSpace == JpegColorSpace.Grayscale ? JpegColorType.Luminance : JpegColorType.YCbCr;
+
                 this.Frame.Init(maxH, maxV);
 
                 this.scanDecoder.InjectFrameData(this.Frame, this);