A tool I coded back in early 1990's to see the structure of a BMP file

bmpdump.pas

{ BMP Header Dumper }
uses Objects,XIO,XTypes;

(*
type
  TBitmapFileHeader = record
    bfType: Word;
    bfSize: Longint;
    bfReserved1: Word;
    bfReserved2: Word;
    bfOffBits: Longint;
  end;

  TRGBQuad = record
    rgbBlue: Byte;
    rgbGreen: Byte;
    rgbRed: Byte;
    rgbReserved: Byte;
  end;

  TRGBTriple = record
    rgbtBlue: Byte;
    rgbtGreen: Byte;
    rgbtRed: Byte;
  end;

  TBitmapCoreHeader = record
    bcSize: Longint;              { used to get to color table }
    bcWidth: longint;
    bcHeight: longint;
    bcPlanes: Word;
    bcBitCount: Word;
  end;
  TBitmapInfoHeader = record
    biCompression: Longint;
    biSizeImage: Longint;
    biXPelsPerMeter: Longint;
    biYPelsPerMeter: Longint;
    biClrUsed: Longint;
    biClrImportant: Longint;
  end;*)

var
  T:TDosStream;
  s:FNameStr;
  TBH:TBMPCore;
  TBS:TBMPSimple;
  TBX:TBMPExtra;
begin
  XAppInit('BMP Dump','1.00d','SSG',1,'filename[.BMP]');
  s := XAddExt(paramstr(1),'.BMP');
  T.Init(s,stOpenRead);
  if T.Status <> stOk then XAbort('unable to read bitmap');
  T.Read(TBH,SizeOf(TBH));
  if TBH.HdrSize > 12 then
  with TBH do begin
    writeln('  FILE HEADER');
    writeln;
    writeln('Bitmap file size       = ',FSize);
    writeln('Reserved word 1        = ',Unknown1);
    writeln('Image offset           = ',DataStart);
    writeln;
    writeln('  CORE HEADER  (New Bitmap Format)');
    writeln;
    writeln('Header size            = ',HdrSize);
    writeln('Image width            = ',SizeX);
    writeln('Image height           = ',SizeY);
    writeln('Number of planes       = ',Planes);
    writeln('Bits per pixel         = ',BitCount,' (',1 shl BitCount,' colors)');
  end else
  with TBS do begin
    T.Seek(0);
    T.Read(TBS,SizeOf(TBS));
    writeln('  FILE HEADER');
    writeln;
    writeln('Bitmap file size       = ',FSize);
    writeln('Reserved word 1        = ',Unknown1);
    writeln('Image offset           = ',DataStart);
    writeln;
    writeln('  CORE HEADER  (Old Bitmap Format)');
    writeln;
    writeln('Header size            = ',HdrSize);
    writeln('Image width            = ',SizeX);
    writeln('Image height           = ',SizeY);
    writeln('Number of planes       = ',Planes);
    writeln('Bits per pixel         = ',BitCount,' (',1 shl BitCount,' colors)');
  end;
  write('Palette type           = ');
  if TBH.HdrSize > 12 then begin
    writeln('Quad');
    writeln;
    T.Read(TBX,SizeOf(TBX));
    with TBX do begin
      writeln('  EXTRA INFORMATION');
      writeln;
      writeln('Compression            = ',Compression);
      writeln('Image size             = ',ImageSize);
      writeln('XPels per meter        = ',XPelspermeter);
      writeln('YPels per meter        = ',YPelspermeter);
      writeln('Used colors            = ',ColorUsed);
      writeln('Important colors       = ',ColorImportant);
    end;
  end else writeln('RGB');
end.