PHP处理bmp格式图片的方法分析

Array
(
  [0] => 494
  [1] => 260
  [2] => 6
  [3] => width="494" height="260"
  [bits] => 24
  [mime] => image/x-ms-bmp
)

<?php
function ImageCreateFromBMP($filename) {
  //Ouverture du fichier en mode binaire
  if (!$f1 = fopen($filename, "rb"))
    return FALSE;
  //1 : Chargement des ent�tes FICHIER
  $FILE = unpack("vfile_type/Vfile_size/Vreserved/Vbitmap_offset", fread($f1, 14));
  if ($FILE['file_type'] != 19778)
    return FALSE;
  //2 : Chargement des ent�tes BMP
  $BMP = unpack('Vheader_size/Vwidth/Vheight/vplanes/vbits_per_pixel' .
      '/Vcompression/Vsize_bitmap/Vhoriz_resolution' .
      '/Vvert_resolution/Vcolors_used/Vcolors_important', fread($f1, 40));
  $BMP['colors'] = pow(2, $BMP['bits_per_pixel']);
  if ($BMP['size_bitmap'] == 0)
    $BMP['size_bitmap'] = $FILE['file_size'] - $FILE['bitmap_offset'];
  $BMP['bytes_per_pixel'] = $BMP['bits_per_pixel'] / 8;
  $BMP['bytes_per_pixel2'] = ceil($BMP['bytes_per_pixel']);
  $BMP['decal'] = ($BMP['width'] * $BMP['bytes_per_pixel'] / 4);
  $BMP['decal'] -= floor($BMP['width'] * $BMP['bytes_per_pixel'] / 4);
  $BMP['decal'] = 4 - (4 * $BMP['decal']);
  if ($BMP['decal'] == 4)
    $BMP['decal'] = 0;
  //3 : Chargement des couleurs de la palette
  $PALETTE = array();
  if ($BMP['colors'] < 16777216) {
    $PALETTE = unpack('V' . $BMP['colors'], fread($f1, $BMP['colors'] * 4));
  }
  //4 : Cr�ation de l'image
  $IMG = fread($f1, $BMP['size_bitmap']);
  $VIDE = chr(0);
  $res = imagecreatetruecolor($BMP['width'], $BMP['height']);
  $P = 0;
  $Y = $BMP['height'] - 1;
  while ($Y >= 0) {
    $X = 0;
    while ($X < $BMP['width']) {
      if ($BMP['bits_per_pixel'] == 24)
        $COLOR = unpack("V", substr($IMG, $P, 3) . $VIDE);
      elseif ($BMP['bits_per_pixel'] == 16) {
        $COLOR = unpack("n", substr($IMG, $P, 2));
        $COLOR[1] = $PALETTE[$COLOR[1] + 1];
      } elseif ($BMP['bits_per_pixel'] == 8) {
        $COLOR = unpack("n", $VIDE . substr($IMG, $P, 1));
        $COLOR[1] = $PALETTE[$COLOR[1] + 1];
      } elseif ($BMP['bits_per_pixel'] == 4) {
        $COLOR = unpack("n", $VIDE . substr($IMG, floor($P), 1));
        if (($P * 2) % 2 == 0)
          $COLOR[1] = ($COLOR[1] >> 4);
        else
          $COLOR[1] = ($COLOR[1] & 0x0F);
        $COLOR[1] = $PALETTE[$COLOR[1] + 1];
      }
      elseif ($BMP['bits_per_pixel'] == 1) {
        $COLOR = unpack("n", $VIDE . substr($IMG, floor($P), 1));
        if (($P * 8) % 8 == 0)
          $COLOR[1] = $COLOR[1] >> 7;
        elseif (($P * 8) % 8 == 1)
          $COLOR[1] = ($COLOR[1] & 0x40) >> 6;
        elseif (($P * 8) % 8 == 2)
          $COLOR[1] = ($COLOR[1] & 0x20) >> 5;
        elseif (($P * 8) % 8 == 3)
          $COLOR[1] = ($COLOR[1] & 0x10) >> 4;
        elseif (($P * 8) % 8 == 4)
          $COLOR[1] = ($COLOR[1] & 0x8) >> 3;
        elseif (($P * 8) % 8 == 5)
          $COLOR[1] = ($COLOR[1] & 0x4) >> 2;
        elseif (($P * 8) % 8 == 6)
          $COLOR[1] = ($COLOR[1] & 0x2) >> 1;
        elseif (($P * 8) % 8 == 7)
          $COLOR[1] = ($COLOR[1] & 0x1);
        $COLOR[1] = $PALETTE[$COLOR[1] + 1];
      } else
        return FALSE;
      imagesetpixel($res, $X, $Y, $COLOR[1]);
      $X++;
      $P += $BMP['bytes_per_pixel'];
    }
    $Y--;
    $P+=$BMP['decal'];
  }
  //Fermeture du fichier
  fclose($f1);
  return $res;
}
$pic = '2.bmp';
$res = ImageCreateFromBMP($pic);
imagepng($res, '1.png');
imagejpeg($res, '1.jpeg');