Begin ProcessStartOfScan

src/ImageSharp/Formats/Jpeg/Port/Components/Component.cs

@@ -49,5 +49,15 @@ namespace ImageSharp.Formats.Jpeg.Port.Components
         /// Gets or sets the number of blocks per column
         /// </summary>
         public int BlocksPerColumn;
+
+        /// <summary>
+        /// Gets the index for the DC Huffman table
+        /// </summary>
+        public int DCHuffmanTableId;
+
+        /// <summary>
+        /// Gets the index for the AC Huffman table
+        /// </summary>
+        public int ACHuffmanTableId;
     }
 }

src/ImageSharp/Formats/Jpeg/Port/JpegConstants.cs

@@ -155,6 +155,24 @@ namespace ImageSharp.Formats.Jpeg.Port
             /// </summary>
             public const ushort DHT = 0xFFC4;
 
+            /// <summary>
+            /// Define Restart Interval
+            /// <remarks>
+            /// Specifies the interval between RSTn markers, in macroblocks.This marker is followed by two bytes indicating the fixed size so it can be treated like any other variable size segment.
+            /// </remarks>
+            /// </summary>
+            public const ushort DRI = 0xFFDD;
+
+            /// <summary>
+            /// Start of Scan
+            /// <remarks>
+            /// Begins a top-to-bottom scan of the image. In baseline DCT JPEG images, there is generally a single scan.
+            /// Progressive DCT JPEG images usually contain multiple scans. This marker specifies which slice of data it
+            /// will contain, and is immediately followed by entropy-coded data.
+            /// </remarks>
+            /// </summary>
+            public const ushort SOS = 0xFFDA;
+
             /// <summary>
             /// Contains JFIF specific markers
             /// </summary>

src/ImageSharp/Formats/Jpeg/Port/JpegDecoderCore.cs

@@ -45,6 +45,8 @@ namespace ImageSharp.Formats.Jpeg.Port
 
         private Frame frame;
 
+        private ushort resetInterval;
+
         /// <summary>
         /// COntains information about the jFIF marker
         /// </summary>
@@ -140,6 +142,14 @@ namespace ImageSharp.Formats.Jpeg.Port
                     case JpegConstants.Markers.DHT:
                         this.ProcessDefineHuffmanTablesMarker(remaining);
                         break;
+
+                    case JpegConstants.Markers.DRI:
+                        this.resetInterval = this.ReadUint16();
+                        break;
+
+                    case JpegConstants.Markers.SOS:
+                        this.ProcessStartOfScan();
+                        break;
                 }
 
                 // Read on
@@ -319,6 +329,8 @@ namespace ImageSharp.Formats.Jpeg.Port
                 component.VerticalFactor = v;
                 component.QuantizationIdentifier = this.temp[index + 2];
 
+                this.frame.ComponentIds[i] = (byte)i;
+
                 // Don't assign the table yet.
                 index += 3;
             }
@@ -374,6 +386,35 @@ namespace ImageSharp.Formats.Jpeg.Port
             }
         }
 
+        /// <summary>
+        /// Processes the SOS (Start of scan marker).
+        /// </summary>
+        private void ProcessStartOfScan()
+        {
+            int selectorsCount = this.InputStream.ReadByte();
+            var components = new List<Component>();
+
+            for (int i = 0; i < selectorsCount; i++)
+            {
+                byte componentIndex = this.frame.ComponentIds[this.InputStream.ReadByte() - 1];
+                Component component = this.frame.Components[componentIndex];
+                int tableSpec = this.InputStream.ReadByte();
+                component.DCHuffmanTableId = tableSpec >> 4;
+                component.ACHuffmanTableId = tableSpec & 15;
+                components.Add(component);
+            }
+
+            this.InputStream.Read(this.temp, 0, 3);
+            int spectralStart = this.temp[0];
+            int spectralEnd = this.temp[1];
+            int successiveApproximation = this.temp[2];
+        }
+
+        private int DecodeScan(List<Component> components, int spectralStart, int spectralEnd, int successivePrev, int successive)
+        {
+            return 0;
+        }
+
         /// <summary>
         /// Builds the huffman tables
         /// </summary>
@@ -555,4 +596,4 @@ namespace ImageSharp.Formats.Jpeg.Port
             // TODO: Thumbnail?
         }
     }
-}
+}