<?php
$im = imagecreatefrompng("ok.png");
imagebmp($im,'ok.bmp',24);


//imagedestroy($im);


/** 
* 建立bmp格式圖片 
* 
* @author: legend([email protected]) 
* @link: http://www.ugia.cn/?p=96 
* @description: create Bitmap-File with GD library 
* @version: 0.1 
* 
* @param resource $im             影象資源 
* @param string      $filename       如果要另存為檔案，請指定檔名，為空則直接在瀏覽器輸出 
* @param integer $bit            影象質量(1、4、8、16、24、32位) 
* @param integer $compression 壓縮方式，0為不壓縮，1使用RLE8壓縮演算法進行壓縮 
* 
* @return integer 
*/ 
function imagebmp(&$im, $filename = '', $bit = 8, $compression = 0) 
{ 
       if (!in_array($bit, array(1, 4, 8, 16, 24, 32))) 
       { 
           $bit = 8; 
       } 
       else if ($bit == 32) // todo:32 bit 
       { 
           $bit = 24; 
       } 


       $bits = pow(2, $bit); 
    
       // 調整調色盤 
       imagetruecolortopalette($im, true, $bits); 
       $width = imagesx($im); 
       $height = imagesy($im); 
       $colors_num = imagecolorstotal($im); 
    $rgb_quad = ''; 
       if ($bit <= 8) 
       { 
           // 顏色索引 
           //$rgb_quad = ''; 
           for ($i = 0; $i < $colors_num; $i ++) 
           { 
               $colors = imagecolorsforindex($im, $i); 
               $rgb_quad .= chr($colors['blue']) . chr($colors['green']) . chr($colors['red']) . "\0"; 
           } 
        
           // 點陣圖資料 
           $bmp_data = ''; 


           // 非壓縮 
           if ($compression == 0 || $bit < 8) 
           { 
               if (!in_array($bit, array(1, 4, 8))) 
               { 
                   $bit = 8; 
               } 


               $compression = 0; 
            
               // 每行位元組數必須為4的倍數，補齊。 
               $extra = ''; 
               $padding = 4 - ceil($width / (8 / $bit)) % 4; 
               if ($padding % 4 != 0) 
               { 
                   $extra = str_repeat("\0", $padding); 
               } 
            
               for ($j = $height - 1; $j >= 0; $j --) 
               { 
                   $i = 0; 
                   while ($i < $width) 
                   { 
                       $bin = 0; 
                       $limit = $width - $i < 8 / $bit ? (8 / $bit - $width + $i) * $bit : 0; 


                       for ($k = 8 - $bit; $k >= $limit; $k -= $bit) 
                       { 
                           $index = imagecolorat($im, $i, $j); 
                           $bin |= $index << $k; 
                           $i ++; 
                       } 


                       $bmp_data .= chr($bin); 
                   } 
                
                   $bmp_data .= $extra; 
               } 
           } 
           // RLE8 壓縮 
           else if ($compression == 1 && $bit == 8) 
           { 
               for ($j = $height - 1; $j >= 0; $j --) 
               { 
                   $last_index = "\0"; 
                   $same_num      = 0; 
                   for ($i = 0; $i <= $width; $i ++) 
                   { 
                       $index = imagecolorat($im, $i, $j); 
                       if ($index !== $last_index || $same_num > 255) 
                       { 
                           if ($same_num != 0) 
                           { 
                               $bmp_data .= chr($same_num) . chr($last_index); 
                           } 


                           $last_index = $index; 
                           $same_num = 1; 
                       } 
                       else 
                       { 
                           $same_num ++; 
                       } 
                   } 


                   $bmp_data .= "\0\0"; 
               } 
            
               $bmp_data .= "\0\1"; 
           } 


           $size_quad = strlen($rgb_quad); 
           $size_data = strlen($bmp_data); 
       } 
       else 
       { 
           // 每行位元組數必須為4的倍數，補齊。 
           $extra = ''; 
           $padding = 4 - ($width * ($bit / 8)) % 4; 
           if ($padding % 4 != 0) 
           { 
               $extra = str_repeat("\0", $padding); 
           } 


           // 點陣圖資料 
           $bmp_data = ''; 


           for ($j = $height - 1; $j >= 0; $j --) 
           { 
               for ($i = 0; $i < $width; $i ++) 
               { 
                   $index = imagecolorat($im, $i, $j); 
                   $colors = imagecolorsforindex($im, $index); 
                
                   if ($bit == 16) 
                   { 
                       $bin = 0 << $bit; 


                       $bin |= ($colors['red'] >> 3) << 10; 
                       $bin |= ($colors['green'] >> 3) << 5; 
                       $bin |= $colors['blue'] >> 3; 


                       $bmp_data .= pack("v", $bin); 
                   } 
                   else 
                   { 
                       $bmp_data .= pack("c*", $colors['blue'], $colors['green'], $colors['red']); 
                   } 
                
                   // todo: 32bit; 
               } 


               $bmp_data .= $extra; 
           } 


           $size_quad = 0; 
           $size_data = strlen($bmp_data); 
           $colors_num = 0; 
       } 


       // 點陣圖檔案頭 
       $file_header = "BM" . pack("V3", 54 + $size_quad + $size_data, 0, 54 + $size_quad); 


       // 點陣圖資訊頭 
       $info_header = pack("V3v2V*", 0x28, $width, $height, 1, $bit, $compression, $size_data, 0, 0, $colors_num, 0); 
    
       // 寫入檔案 
       if ($filename != '') 
       { 
           $fp = fopen($filename, "wb"); 


           fwrite($fp, $file_header); 
           fwrite($fp, $info_header); 
           fwrite($fp, $rgb_quad); 
           fwrite($fp, $bmp_data); 
           fclose($fp); 


           return 1; 
       } 
    
       // 瀏覽器輸出 
       header("Content-Type: image/bmp"); 
       echo $file_header . $info_header; 
       echo $rgb_quad; 
       echo $bmp_data; 
    
       return 1; 
}