More jpeg work.

@thumbnails

 Need sleep!

Codecs/Image/Jpeg/Classes/ThumbnailFormat.cs

@@ -0,0 +1,10 @@
+namespace Codec.Jpeg.Classes;
+
+public enum ThumbnailFormatType : int
+{
+    Jpeg = 10,
+    Palette = 11,
+    RGB = 13,
+    YCbCr = 21,
+    CieLab = 22
+}

Codecs/Image/Jpeg/JpegImage.cs

@@ -117,6 +117,22 @@ public static JpegImage FromStream(Stream stream)
                     }
                 case Jpeg.Markers.AppFirst:
                 case Jpeg.Markers.AppLast:
+                    var app = new App(marker);
+
+                    if(app.MajorVersion >= 1 && app.MinorVersion >= 2)
+                    {
+                        var appExtension = new AppExtension(app);
+                        var thumbnailData = appExtension.ThumbnailData;
+                        dataSegment = thumbnailData;
+                    }
+                    else
+                    {
+                        var thumbnailData = app.ThumbnailData;
+                        dataSegment = thumbnailData;
+                        imageFormat = ImageFormat.RGB(8);
+                        width = app.XThumbnail;
+                        height = app.YThumbnail;
+                    }
 
                     break;
                 default:

Codecs/Image/Jpeg/Markers/App.cs

@@ -0,0 +1,85 @@
+using Media.Codec.Jpeg;
+using Media.Common;
+using System;
+using System.Text;
+
+namespace Codec.Jpeg.Markers;
+
+public class App : Marker
+{
+    public new const int Length = 14;
+
+    public string Identifier
+    {
+        get => Encoding.UTF8.GetString(Data.Array, Data.Offset, 5);
+        set => Encoding.UTF8.GetBytes(value, 0, 5, Data.Array, Data.Offset);
+    }
+
+    public byte MajorVersion
+    {
+        get => Data[6];
+        set => Data[6] = value;
+    }
+
+    public byte MinorVersion
+    {
+        get => Data[7];
+        set => Data[7] = value;
+    }
+
+    public Version Version
+    {
+        get => new Version(MajorVersion, MinorVersion);
+        set
+        {
+            MajorVersion = (byte)value.Major;
+            MinorVersion = (byte)value.Minor;
+        }
+    }
+
+    public int DensityUnits
+    {
+        get => Data[8];
+        set => Data[8] = (byte)value;
+    }
+
+    public int XDensity
+    {
+        get => Binary.Read16(Data.Array, Data.Offset + 9, Binary.IsLittleEndian);
+        set => Binary.Write16(Data.Array, Data.Offset + 9, Binary.IsLittleEndian, (ushort)value);
+    }
+
+    public int YDensity
+    {
+        get => Binary.Read16(Data.Array, Data.Offset + 11, Binary.IsLittleEndian);
+        set => Binary.Write16(Data.Array, Data.Offset + 11, Binary.IsLittleEndian, (ushort)value);
+    }
+
+    public int XThumbnail
+    {
+        get => Data[12];
+        set => Data[12] = (byte)value;
+    }
+
+    public int YThumbnail
+    {
+        get => Data[13];
+        set => Data[13] = (byte)value;
+    }
+
+    public MemorySegment ThumbnailData
+    {
+        get => Data.Slice(14);
+        set => value.CopyTo(Data.Array, Data.Offset + 14);
+    }
+
+    public App(byte functionCode, MemorySegment data)
+        : base(functionCode, Length + data.Count)
+    {
+        data.CopyTo(Data.Array, Data.Offset + 14);
+    }
+
+    public App(Marker marker) : base(marker)
+    {
+    }
+}

Codecs/Image/Jpeg/Markers/AppExtension.cs

@@ -0,0 +1,50 @@
+using Codec.Jpeg.Classes;
+using Media.Codec.Jpeg;
+using Media.Common;
+using System.Text;
+
+namespace Codec.Jpeg.Markers;
+
+internal class AppExtension : Marker
+{
+    public new const int Length = 6;
+
+    public AppExtension(byte functionCode, MemorySegment data)
+        : base(functionCode, Length + data.Count)
+    {
+        data.CopyTo(ThumbnailData);
+    }
+
+    public AppExtension(MemorySegment data)
+        : base(data)
+    {
+    }
+
+    public string Identifier
+    {
+        get => Encoding.UTF8.GetString(Data.Array, Data.Offset, 5);
+        set => Encoding.UTF8.GetBytes(value, 0, 5, Data.Array, Data.Offset);
+    }
+
+    public int ThumbnailFormat
+    {
+        get => Data[6];
+        set => Data[6] = (byte)value;
+    }
+
+    public ThumbnailFormatType ThumbnailFormatType
+    {
+        get => (ThumbnailFormatType)ThumbnailFormat;
+        set => ThumbnailFormat = (int)value;
+    }
+
+    public MemorySegment ThumbnailData
+    {
+        get => Data.Slice(DataSize > 0 ? 6 : 0);
+        set
+        {
+            using var slice = ThumbnailData;
+            value.CopyTo(slice);
+        }
+    }
+}