procedure Warning(Severity: TGIFSeverity; Message: string); virtual; abstract;
    procedure BuildHistogram(var Histogram: TColormapHistogram); virtual; abstract;
    procedure MapImages(var Map: TColormapReverse); virtual; abstract;

  public
    constructor Create;
    destructor Destroy; override;
    class function Color2RGB(Color: TColor): TGIFColor;
    class function RGB2Color(Color: TGIFColor): TColor;
    procedure SaveToStream(Stream: TStream);
    procedure LoadFromStream(Stream: TStream; Count: integer);
    procedure Assign(Source: TPersistent); override;
    function IndexOf(Color: TColor): integer;
    function Add(Color: TColor): integer;
    function AddUnique(Color: TColor): integer;
    procedure Delete(Index: integer);
    procedure Clear;
    function Optimize: boolean; virtual; abstract;
    procedure Changed; virtual; abstract;
    procedure ImportPalette(Palette: HPalette);
    procedure ImportColorTable(Pal: pointer; Count: integer);
    procedure ImportDIBColors(Handle: HDC);
    procedure ImportColorMap(Map: TColorMap; Count: integer);
    function ExportPalette: HPalette;
    property Colors[Index: integer]: TColor read GetColor write SetColor; default;
    property Data: PColorMap read FColorMap;
    property Count: integer read FCount;
    property Optimized: boolean read FOptimized write FOptimized;
    property BitsPerPixel: integer read GetBitsPerPixel;
  end;

////////////////////////////////////////////////////////////////////////////////
//
//			TGIFHeader
//
////////////////////////////////////////////////////////////////////////////////
  TLogicalScreenDescriptor = packed record
    ScreenWidth: word;              { logical screen width }
    ScreenHeight: word;             { logical screen height }
    PackedFields: byte;             { packed fields }
    BackgroundColorIndex: byte;     { index to global color table }
    AspectRatio: byte;              { actual ratio = (AspectRatio + 15) / 64 }
  end;

  TGIFHeader = class(TGIFItem)
  private
    FLogicalScreenDescriptor: TLogicalScreenDescriptor;
    FColorMap		: TGIFColorMap;
    procedure Prepare;
  protected
    function GetVersion: TGIFVersion; override;
    function GetBackgroundColor: TColor;
    procedure SetBackgroundColor(Color: TColor);
    procedure SetBackgroundColorIndex(Index: BYTE);
    function GetBitsPerPixel: integer;
    function GetColorResolution: integer;
  public
    constructor Create(GIFImage: TGIFImage); override;
    destructor Destroy; override;
    procedure Assign(Source: TPersistent); override;
    procedure SaveToStream(Stream: TStream); override;
    procedure LoadFromStream(Stream: TStream); override;
    procedure Clear;
    property Version: TGIFVersion read GetVersion;
    property Width: WORD read FLogicalScreenDescriptor.ScreenWidth
                         write FLogicalScreenDescriptor.ScreenWidth;
    property Height: WORD read FLogicalScreenDescriptor.ScreenHeight
                          write FLogicalScreenDescriptor.Screenheight;
    property BackgroundColorIndex: BYTE read FLogicalScreenDescriptor.BackgroundColorIndex
                                        write SetBackgroundColorIndex;
    property BackgroundColor: TColor read GetBackgroundColor
                                     write SetBackgroundColor;
    property AspectRatio: BYTE read FLogicalScreenDescriptor.AspectRatio
                               write FLogicalScreenDescriptor.AspectRatio;
    property ColorMap: TGIFColorMap read FColorMap;
    property BitsPerPixel: integer read GetBitsPerPixel;
    property ColorResolution: integer read GetColorResolution;
  end;

////////////////////////////////////////////////////////////////////////////////
//
//                      TGIFExtension
//
////////////////////////////////////////////////////////////////////////////////
  TGIFExtensionType = BYTE;
  TGIFExtension = class;
  TGIFExtensionClass = class of TGIFExtension;

  TGIFGraphicControlExtension = class;

  TGIFExtension = class(TGIFItem)
  private
    FSubImage: TGIFSubImage;
  protected
    function GetExtensionType: TGIFExtensionType; virtual; abstract;
    function GetVersion: TGIFVersion; override;
    function DoReadFromStream(Stream: TStream): TGIFExtensionType;
    class procedure RegisterExtension(elabel: BYTE; eClass: TGIFExtensionClass);
    class function FindExtension(Stream: TStream): TGIFExtensionClass;
    class function FindSubExtension(Stream: TStream): TGIFExtensionClass; virtual;
  public
     // Ignore compiler warning about hiding base class constructor
    constructor Create(ASubImage: TGIFSubImage); {$IFDEF VER12_PLUS} reintroduce; {$ENDIF} virtual;
    destructor Destroy; override;
    procedure SaveToStream(Stream: TStream); override;
    procedure LoadFromStream(Stream: TStream); override;
    property ExtensionType: TGIFExtensionType read GetExtensionType;
    property SubImage: TGIFSubImage read FSubImage;
  end;

////////////////////////////////////////////////////////////////////////////////
//
//			TGIFSubImage
//
////////////////////////////////////////////////////////////////////////////////
  TGIFExtensionList = class(TGIFList)
  protected
    function GetExtension(Index: Integer): TGIFExtension;
    procedure SetExtension(Index: Integer; Extension: TGIFExtension);
  public
    procedure LoadFromStream(Stream: TStream; Parent: TObject); override;
    property Extensions[Index: Integer]: TGIFExtension read GetExtension write SetExtension; default;
  end;

  TImageDescriptor = packed record
    Separator: byte;	{ fixed value of ImageSeparator }
    Left: word;		{ Column in pixels in respect to left edge of logical screen }
    Top: word;		{ row in pixels in respect to top of logical screen }
    Width: word;	{ width of image in pixels }
    Height: word;	{ height of image in pixels }
    PackedFields: byte;	{ Bit fields }
  end;

  TGIFSubImage = class(TGIFItem)
  private
    FBitmap		: TBitmap;
    FMask		: HBitmap;
    FNeedMask		: boolean;
    FLocalPalette	: HPalette;
    FData		: PChar;
    FDataSize		: integer;
    FColorMap		: TGIFColorMap;
    FImageDescriptor	: TImageDescriptor;
    FExtensions		: TGIFExtensionList;
    FTransparent	: boolean;
    FGCE		: TGIFGraphicControlExtension;
    procedure Prepare;
    procedure Compress(Stream: TStream);
    procedure Decompress(Stream: TStream);
  protected
    function GetVersion: TGIFVersion; override;
    function GetInterlaced: boolean;
    procedure SetInterlaced(Value: boolean);
    function GetColorResolution: integer;
    function GetBitsPerPixel: integer;
    procedure AssignTo(Dest: TPersistent); override;
    function DoGetBitmap: TBitmap;
    function DoGetDitherBitmap: TBitmap;
    function GetBitmap: TBitmap;
    procedure SetBitmap(Value: TBitmap);
    procedure FreeMask;
    function GetEmpty: Boolean;
    function GetPalette: HPALETTE;
    procedure SetPalette(Value: HPalette);
    function GetActiveColorMap: TGIFColorMap;
    function GetBoundsRect: TRect;
    procedure SetBoundsRect(const Value: TRect);
    procedure DoSetBounds(ALeft, ATop, AWidth, AHeight: integer);
    function GetClientRect: TRect;
    function GetPixel(x, y: integer): BYTE;
    function GetScanline(y: integer): pointer;
    procedure NewBitmap;
    procedure FreeBitmap;
    procedure NewImage;
    procedure FreeImage;
    procedure NeedImage;
    function ScaleRect(DestRect: TRect): TRect;
    function HasMask: boolean;
    function GetBounds(Index: integer): WORD;
    procedure SetBounds(Index: integer; Value: WORD);
    function GetHasBitmap: boolean;
    procedure SetHasBitmap(Value: boolean);
  public
    constructor Create(GIFImage: TGIFImage); override;
    destructor Destroy; override;
    procedure Clear;
    procedure SaveToStream(Stream: TStream); override;
    procedure LoadFromStream(Stream: TStream); override;
    procedure Assign(Source: TPersistent); override;
    procedure Draw(ACanvas: TCanvas; const Rect: TRect;
      DoTransparent, DoTile: boolean);
    procedure StretchDraw(ACanvas: TCanvas; const Rect: TRect;
      DoTransparent, DoTile: boolean);
    procedure Crop;
    procedure Merge(Previous: TGIFSubImage);
    property HasBitmap: boolean read GetHasBitmap write SetHasBitmap;
    property Left: WORD index 1 read GetBounds write SetBounds;
    property Top: WORD index 2 read GetBounds write SetBounds;
    property Width: WORD index 3 read GetBounds write SetBounds;
    property Height: WORD index 4 read GetBounds write SetBounds;
    property BoundsRect: TRect read GetBoundsRect write SetBoundsRect;
    property ClientRect: TRect read GetClientRect;
    property Interlaced: boolean read GetInterlaced write SetInterlaced;
    property ColorMap: TGIFColorMap read FColorMap;
    property ActiveColorMap: TGIFColorMap read GetActiveColorMap;
    property Data: PChar read FData;
    property DataSize: integer read FDataSize;
    property Extensions: TGIFExtensionList read FExtensions;
    property Version: TGIFVersion read GetVersion;
    property ColorResolution: integer read GetColorResolution;
    property BitsPerPixel: integer read GetBitsPerPixel;
    property Bitmap: TBitmap read GetBitmap write SetBitmap;
    property Mask: HBitmap read FMask;
    property Palette: HPALETTE read GetPalette write SetPalette;
    property Empty: boolean read GetEmpty;
    property Transparent: boolean read FTransparent;
    property GraphicControlExtension: TGIFGraphicControlExtension read FGCE;
    property Pixels[x, y: integer]: BYTE read GetPixel;
    property Scanline[y: integer]: pointer read GetScanline;
  end;

////////////////////////////////////////////////////////////////////////////////
//
//                      TGIFTrailer
//
////////////////////////////////////////////////////////////////////////////////
  TGIFTrailer = class(TGIFItem)
    procedure SaveToStream(Stream: TStream); override;
    procedure LoadFromStream(Stream: TStream); override;
  end;

////////////////////////////////////////////////////////////////////////////////
//
//                      TGIFGraphicControlExtension
//
////////////////////////////////////////////////////////////////////////////////
  // Graphic Control Extension block a.k.a GCE
  TGIFGCERec = packed record
    BlockSize: byte;         { should be 4 }
    PackedFields: Byte;
    DelayTime: Word;         { in centiseconds }
    TransparentColorIndex: Byte;
    Terminator: Byte;
  end;

  TDisposalMethod = (dmNone, dmNoDisposal, dmBackground, dmPrevious);

  TGIFGraphicControlExtension = class(TGIFExtension)
  private
    FGCExtension: TGIFGCERec;
  protected
    function GetExtensionType: TGIFExtensionType; override;
    function GetTransparent: boolean;
    procedure SetTransparent(Value: boolean);
    function GetTransparentColor: TColor;
    procedure SetTransparentColor(Color: TColor);
    function GetTransparentColorIndex: BYTE;
    procedure SetTransparentColorIndex(Value: BYTE);
    function GetDelay: WORD;
    procedure SetDelay(Value: WORD);
    function GetUserInput: boolean;
    procedure SetUserInput(Value: boolean);
    function GetDisposal: TDisposalMethod;
    procedure SetDisposal(Value: TDisposalMethod);

  public
    constructor Create(ASubImage: TGIFSubImage); override;
    destructor Destroy; override;
    procedure SaveToStream(Stream: TStream); override;
    procedure LoadFromStream(Stream: TStream); override;
    property Delay: WORD read GetDelay write SetDelay;
    property Transparent: boolean read GetTransparent write SetTransparent;
    property TransparentColorIndex: BYTE read GetTransparentColorIndex
                                            write SetTransparentColorIndex;
    property TransparentColor: TColor read GetTransparentColor write SetTransparentColor;
    property UserInput: boolean read GetUserInput write SetUserInput;
    property Disposal: TDisposalMethod read GetDisposal write SetDisposal;
  end;

////////////////////////////////////////////////////////////////////////////////
//
//                      TGIFTextExtension
//
////////////////////////////////////////////////////////////////////////////////
  TGIFPlainTextExtensionRec = packed record
    BlockSize: byte;         { should be 12 }
    Left, Top, Width, Height: Word;
    CellWidth, CellHeight: Byte;
    TextFGColorIndex,
    TextBGColorIndex: Byte;
  end;

  TGIFTextExtension = class(TGIFExtension)
  private
    FText		: TStrings;
    FPlainTextExtension	: TGIFPlainTextExtensionRec;
  protected
    function GetExtensionType: TGIFExtensionType; override;
    function GetForegroundColor: TColor;
    procedure SetForegroundColor(Color: TColor);
    function GetBackgroundColor: TColor;
    procedure SetBackgroundColor(Color: TColor);
    function GetBounds(Index: integer): WORD;