exif.pas

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{==============================================================================
Component simple read Exif section in Jpeg/Jfif Files.
More information about Exif at www.exif.org


裲mponent written by SimBa aka Dimoniusis
You may use this component absolutely free.

You may talk with me via
e-mail: [e-mail]
ICQ: 11152101
Web: http://dimonius.da.ru


Changes:
Version 1.3 
 - some more ifd tags implemented
 - some bugs fixes

Version 1.2 (Some code by Jim Wood,  e-mail: [e-mail])
 - some more ifd tags implemented
 - corrected work with ReadOnly files

Version 1.1 (By Ive, e-mail: [e-mail])
 - works now with Motorola and Intel byte order tags
 - better offset calculation
 - some more ifd tags implemented
 - some format functions for rational values
 - naming convention changed a little


NOTE: far away from being complete but it seems to
      work with all example files from www.exif.org

 - Ive (c) 2003




==============================================================================}

unit Exif;

interface

uses
  Classes, SysUtils;

type
  TIfdTag = packed record
    ID      : Word;       //Tag number
    Typ     : Word;       //Type tag
    Count   : Cardinal;   //tag length
    Offset  : Cardinal;   //Offset / Value
  end;

  TExif = class(TObject)
    private
      FImageDesc          : String;     //Picture description
      FMake               : String;     //Camera manufacturer
      FModel              : String;     //Camere model
      FOrientation        : Byte;       //Image orientation - 1 normal
      FOrientationDesc    : String;     //Image orientation description
      FCopyright          : String;     //Copyright
      FValid              : Boolean;    //Has valid Exif header
      FDateTime           : String;     //Date and Time of Change
      FDateTimeOriginal   : String;     //Original Date and Time
      FDateTimeDigitized  : String;     //Camshot Date and Time
      FUserComments       : String;     //User Comments

      FExposure           : String;     //Exposure
      FFstops             : String;
      FShutterSpeed       : string;
      FAperture           : string;
      FMaxAperture        : string;

      FExposureProgram    : Byte;
      FExposureProgramDesc: string;
      FPixelXDimension    : Cardinal;
      FPixelYDimension    : Cardinal;
      FXResolution        : Cardinal;
      FYResolution        : Cardinal;
      FMeteringMode       : byte;
      FMeteringMethod     : string;
      FLightSource        : Byte;
      FLightSourceDesc    : string;
      FFlash              : Byte;
      FFlashDesc          : string;
      FISO                : Word;
      FSoftware           : string;
      FArtist             : string;
      FCompressedBPP      : string;


      f                   : File;
      ifdp                : Cardinal;
      FSwap               : boolean;
      function  ReadAsci(const Offset, Count: Cardinal): String;
      function  ReadRatio(const Offset: Cardinal; frac: boolean): String; overload;
      function  ReadRatio(const Offset: Cardinal): single; overload;
      procedure ReadTag(var tag: TIfdTag);
      procedure Init;
    function ReadLongIntValue(const Offset: Cardinal): LongInt;
    public
      constructor Create;
      procedure ReadFromFile(const FileName: AnsiString);

      property Valid: Boolean read FValid;
      property ImageDesc: String read FImageDesc;
      property Make: String read FMake;
      property Model: String read FModel;
      property Orientation: Byte read FOrientation;
      property OrientationDesc: String read FOrientationDesc;
      property Copyright: String read FCopyright;
      property DateTime: String read FDateTime;
      property DateTimeOriginal: String read FDateTimeOriginal;
      property DateTimeDigitized: String read FDateTimeDigitized;
      property UserComments: String read FUserComments;
      property Software: String read FSoftware;
      property Artist: String read FArtist;

      property Exposure: String read FExposure;
      property ExposureProgram: byte read FExposureProgram;
      property ExposureProgramDesc: string read FExposureProgramDesc;
      property FStops: String read FFStops;
      property ShutterSpeed: String read FShutterSpeed;
      property Aperture: String read FAperture;
      property MaxAperture: String read FMaxAperture;
      property CompressedBPP: String read FCompressedBPP;

      property PixelXDimension: Cardinal read FPixelXDimension;
      property PixelYDimension: Cardinal read FPixelYDimension;
      property XResolution: Cardinal read FXResolution;
      property YResolution: Cardinal read FYResolution;
      property MeteringMode: byte read FMeteringMode;
      property MeteringMethod: string read FMeteringMethod;
      property LightSource: byte read FLightSource;
      property LightSourceDesc: string read FLightSourceDesc;
      property Flash: byte read FFlash;
      property FlashDesc: string read FFlashDesc;
      property ISO: Word read FISO;
  end;

implementation

uses
  Math;

type
  TMarker = packed record
    Marker  : Word;      //Section marker
    Len     : Word;      //Length Section
    Indefin : Array [0..4] of Char; //Indefiner - "Exif" 00, "JFIF" 00 and ets
    Pad     : Char;      //0x00
  end;

  TIFDHeader = packed record
    pad       : Byte; //00h
    ByteOrder : Word; //II (4D4D) or MM
    i42       : Word; //2A00 (magic number from the 'Hitchhikers Guide'
    Offset    : Cardinal; //0th offset IFD
    Count     : Word;     // number of IFD entries
  end;


function SwapLong(Value: Cardinal): Cardinal;
asm bswap eax end;

procedure TExif.ReadTag(var tag: TIfdTag);
begin
  BlockRead(f,tag,12);
  if FSwap then with tag do begin // motorola or intel byte order ?
    ID  := Swap(ID);
    Typ := Swap(Typ);
    Count := SwapLong(Count);
    if (Typ=1) or (Typ=3) then
      Offset := (Offset shr 8) and $FF
    else
      Offset  := SwapLong(Offset);
    end
  else with tag do begin
    if ID<>$8827 then  //ISO Metering Mode not need conversion
      if (Typ=1) or (Typ=3) then
        Offset := Offset and $FF; // other bytes are undefined but maybe not zero
  end;
end;


function TExif.ReadAsci(const Offset, Count: Cardinal): String;
var
  fp: LongInt;
  i: Word;
begin
  SetLength(Result,Count);
  fp:=FilePos(f); //Save file offset
  Seek(f, Offset);
  try
    i:=1;
    repeat
      BlockRead(f,Result[i],1);
      inc(i);
    until (i>=Count) or (Result[i-1]=#0);
    if i<=Count then Result:=Copy(Result,1,i-1);
  except
    Result:='';
  end;
  Result:=TrimRight(Result);
  Seek(f,fp);     //Restore file offset
end;

function TExif.ReadLongIntValue(const Offset: Cardinal): LongInt;
var
  fp: LongInt;
begin
  fp:=FilePos(f); //Save file offset
  Seek(f, Offset);
  try
    BlockRead(f, Result, sizeof(Result));
    if FSwap then Result:=SwapLong(Result);
  except
    Result:=0;
  end;
  Seek(f, fp); //Restore file offset
end;

function TExif.ReadRatio(const Offset: Cardinal; frac: boolean): String;
var
  fp: LongInt;
  nom,denom: cardinal;
begin
  fp:=FilePos(f); //Save file offset
  Seek(f, Offset);
  try
    BlockRead(f,nom,4);
    BlockRead(f,denom,4);
    if FSwap then begin     // !!!
      nom := SwapLong(nom);
      denom := SwapLong(denom);
    end;
    if frac then begin
      str((nom/denom):1:2, result);
      if (length(result)>0) and (result[length(result)]='0') then Result:=copy(Result,1,length(Result)-1);
    end else
      if denom<>1000000 then
        Result:=inttostr(nom)+'/'+inttostr(denom)
      else Result:='0';
  except
    Result:='';
  end;
  Seek(f,fp);     //Restore file offset
end;


function TExif.ReadRatio(const Offset: Cardinal): single;
var
  fp: LongInt;
  nom,denom: cardinal;
begin
  fp:=FilePos(f); //Save file offset
  Seek(f, Offset);
  try
    BlockRead(f,nom,4);
    BlockRead(f,denom,4);
    if FSwap then begin     // !!!
      nom := SwapLong(nom);
      denom := SwapLong(denom);
    end;
    Result:=nom/denom;