BMP Image Format

Unit: BMP

Loads/saves Windows BMP files (256-color indexed, uncompressed).

Types

type
  TBMPFileHeader = record
    bfType: Word;           { 'BM' = $4D42 }
    bfSize: LongInt;        { File size }
    bfReserved1: Word;
    bfReserved2: Word;
    bfOffBits: LongInt;     { Offset to pixel data }
  end;

  TBMPInfoHeader = record
    biSize: LongInt;        { Header size (40) }
    biWidth: LongInt;
    biHeight: LongInt;
    biPlanes: Word;         { 1 }
    biBitCount: Word;       { 8 (256 colors) }
    biCompression: LongInt; { 0 = BI_RGB (uncompressed) }
    biSizeImage: LongInt;
    biXPelsPerMeter: LongInt;
    biYPelsPerMeter: LongInt;
    biClrUsed: LongInt;     { 0 or 256 }
    biClrImportant: LongInt;
  end;

  TBMPRGBQuad = record
    rgbBlue: Byte;
    rgbGreen: Byte;
    rgbRed: Byte;
    rgbReserved: Byte;      { 0 }
  end;

Functions

function LoadBMP(const FileName: string; var Img: TImage): Boolean;
function LoadBMPWithPalette(const FileName: string; var Img: TImage; var Pal: TPalette): Boolean;
function GetLoadBMPError: string;

function SaveBMP(const FileName: string; const Img: TImage; const Pal: TPalette): Boolean;
function GetSaveBMPError: string;

Example

uses BMP, VGA;

var
  Img: TImage;
  Pal: TPalette;
begin
  InitVGA;

  if not LoadBMPWithPalette('PLAYER.BMP', Img, Pal) then
  begin
    WriteLn('Error: ', GetLoadBMPError);
    DoneVGA;
    Exit;
  end;

  SetPalette(Pal);
  PutImage(0, 0, @Img, GetScreenBuffer);
  ReadKey;

  SaveBMP('OUTPUT.BMP', Img, Pal);

  FreeImage(@Img);
  DoneVGA;
end;

Format Details

8-bit indexed color (256 colors)
BI_RGB (uncompressed)
Bottom-up scanlines (first scanline = bottom row)
4-byte alignment per scanline (padded)
BGRA palette (Blue, Green, Red, Reserved)

Palette Conversion

BMP uses BGRA format (0-255), VGA uses RGB (0-63). Automatic conversion:

{ BMP → VGA }
Pal[i].R := BMPPalette[i].rgbRed shr 2;
Pal[i].G := BMPPalette[i].rgbGreen shr 2;
Pal[i].B := BMPPalette[i].rgbBlue shr 2;

{ VGA → BMP }
BMPPalette[i].rgbRed := Pal[i].R shl 2;
BMPPalette[i].rgbGreen := Pal[i].G shl 2;
BMPPalette[i].rgbBlue := Pal[i].B shl 2;

Creating BMP Files

Windows Paint

Image → Resize → 256 colors
Save As → 24-bit BMP (auto-converts to 8-bit)

GIMP

Image → Mode → Indexed (256 colors)
File → Export As → .bmp
Options: 8 bits, no color space info

Photoshop

Image → Mode → Indexed Color
File → Save As → BMP
Format: Windows, 8 bits/pixel

BMP vs PCX

Feature	BMP	PCX
Compression	None	RLE
Scanlines	Bottom-up	Top-down
Palette	BGRA (0-255)	RGB (0-255)
Tools	Paint, Photoshop	Aseprite, GIMP
File Size	Larger	Smaller

Notes

Max image size: 320×204 (65520 bytes) due to TImage limits
Handles scanline padding (4-byte alignment) automatically
Compatible with Windows Paint, Photoshop, GIMP
For RLE compression, use PCX format instead