php bmp图片格式转化png

有gd库不支持bmp格式的图片缩放，裁剪，所以可以通过改变图片格式，然后再裁剪

以下是吧bmp格式的图片裁剪成png格式：



<?php
function ConvertBMP2GD($src, $dest = false) {
if(!($src_f = fopen($src, "rb"))) {
  return false;
}
if(!($dest_f = fopen($dest, "wb"))) {
  return false;
}
$header = unpack("vtype/Vsize/v2reserved/Voffset", fread($src_f, 14));
$info = unpack("Vsize/Vwidth/Vheight/vplanes/vbits/Vcompression/Vimagesize/Vxres/Vyres/Vncolor/Vimportant", fread($src_f, 40));
extract($info);
extract($header);
if($type != 0x4D42) { // signature "BM"
  return false;
}
$palette_size = $offset - 54;
$ncolor = $palette_size / 4;
$gd_header = "";
// true-color vs. palette
$gd_header .= ($palette_size == 0) ? "\xFF\xFE" : "\xFF\xFF";
$gd_header .= pack("n2", $width, $height);
$gd_header .= ($palette_size == 0) ? "\x01" : "\x00";
if($palette_size) {
  $gd_header .= pack("n", $ncolor);
}
// no transparency
$gd_header .= "\xFF\xFF\xFF\xFF";
fwrite($dest_f, $gd_header);
if($palette_size) {
  $palette = fread($src_f, $palette_size);
  $gd_palette = "";
  $j = 0;
  while($j < $palette_size) {
   $b = $palette{$j++};
   $g = $palette{$j++};
   $r = $palette{$j++};
   $a = $palette{$j++};
   $gd_palette .= "$r$g$b$a";
  }
  $gd_palette .= str_repeat("\x00\x00\x00\x00", 256 - $ncolor);
  fwrite($dest_f, $gd_palette);
}
$scan_line_size = (($bits * $width) + 7) >> 3;
$scan_line_align = ($scan_line_size & 0x03) ? 4 - ($scan_line_size & 0x03) : 0;
for($i = 0, $l = $height - 1; $i < $height; $i++, $l--) {
// BMP stores scan lines starting from bottom
  fseek($src_f, $offset + (($scan_line_size + $scan_line_align) * $l));
  $scan_line = fread($src_f, $scan_line_size);
  if($bits == 24) {
   $gd_scan_line = "";
   $j = 0;
   while($j < $scan_line_size) {
    $b = $scan_line{$j++};
    $g = $scan_line{$j++};
    $r = $scan_line{$j++};
    $gd_scan_line .= "\x00$r$g$b";
   }
  }
  else if($bits == {
   $gd_scan_line = $scan_line;
  }
  else if($bits == 4) {
   $gd_scan_line = "";
   $j = 0;
   while($j < $scan_line_size) {
    $byte = ord($scan_line{$j++});
    $p1 = chr($byte >> 4);
    $p2 = chr($byte & 0x0F);
    $gd_scan_line .= "$p1$p2";
   }
   $gd_scan_line = substr($gd_scan_line, 0, $width);
  }
  else if($bits == 1) {
   $gd_scan_line = "";
   $j = 0;
   while($j < $scan_line_size) {
    $byte = ord($scan_line{$j++});
    $p1 = chr((int) (($byte & 0x80) != 0));
    $p2 = chr((int) (($byte & 0x40) != 0));
    $p3 = chr((int) (($byte & 0x20) != 0));
    $p4 = chr((int) (($byte & 0x10) != 0));
    $p5 = chr((int) (($byte & 0x08) != 0));
    $p6 = chr((int) (($byte & 0x04) != 0));
    $p7 = chr((int) (($byte & 0x02) != 0));
    $p8 = chr((int) (($byte & 0x01) != 0));
    $gd_scan_line .= "$p1$p2$p3$p4$p5$p6$p7$p8";
   }
   $gd_scan_line = substr($gd_scan_line, 0, $width);
  }
  fwrite($dest_f, $gd_scan_line);
}
fclose($src_f);
fclose($dest_f);
return true;
}
function imagecreatefrombmp($filename) {
$tmp_name = tempnam("tmp", "GD");
if(ConvertBMP2GD($filename, $tmp_name)) {
  $img = imagecreatefromgd($tmp_name);
  unlink($tmp_name);
  return $img;
}
return false;
}
function mylog($msg)   // 偶加的
{
$fp = fopen("mylog.txt", "a+");
echo $msg."\n";
fwrite($fp, $msg."\n");
fclose($fp);
}
$img = imagecreatefrombmp("test24bit.bmp");
if($img)
{
imagepng($img, "./test.png");  //原文是转成jpeg
}
?>



出处：
http://blog.sina.com.cn/s/blog_48d7f3f40100o6at.html