// Display 16 color bars in a pf4bit bitmap
// efg, 6 October 1998

procedure TForm1.ButtonPf4bitClick(Sender: TObject);
  VAR
    Bitmap:  TBitmap;
    i,j   :  INTEGER;
    m     :  INTEGER;
    row   :  pByteArray;    // each pixel is a "nibble" (that is, a half byte)
begin
  Bitmap := TBitmap.Create;
  TRY
    Bitmap.Width  := Image1.Width;
    Bitmap.Height := Image1.Height;  // Should be multiple of 16
    Bitmap.PixelFormat := pf4bit;    // 16 colors

    FOR j := 0 TO Bitmap.Height-1 DO
    BEGIN
      m := j DIV 16;      // 16 bands:  0 .. 15
      row := Bitmap.Scanline[j];
      FOR i := 0 TO Bitmap.Width DIV 2 - 1 DO  // 2 pixels per byte
      BEGIN
        row[i] := m         + {low  nibble pixel}
                  (m SHL 4);  {high nibble pixel}
      END
    END;

    Image1.Picture.Graphic := Bitmap
  FINALLY
    Bitmap.Free
  END
end;