仿GD讀取bmp函數

最近在工作上需要把bmp圖片轉成jpg圖片，但無奈的是網路上能找到的bmp轉gd的類別或函數或多或少都有些問題。其中絕大多數在處理16位元bmp圖片時要麼全黑全粉，要麼乾脆轉換不出，其餘有些根本不支援32位元的bmp圖片。
最後我終於在php的官網上找到解決方法了。原來網路上流傳最廣的一個仿GD的imagecreatefrombmp函數是一個有問題的版本，無法正確處理16位元bmp圖片，但好在官網上有人給出了修正方法，修正好的程式碼如下：

/**
 * BMP 建立函數
 * @author simon
 * @modified by 天心流水
 * @param string $filename path of bmp file
 * @example who use,who knows*/
function imagecreatefrombmp( $filename ) {
 if ( !$f1 = fopen( $filename, "rb" ) )
 return FALSE;

 $FILE = unpack( "vfile_type/Vfile_size/Vreserved/Vbitmap_offset", fread( $f1, 14 ) );
 if ( $FILE['file_type' 78 )
 return FALSE;

 $BMP = unpack( 'Vheader_size/Vwidth/Vheight/vplanes/vbits_per_pixel' . '/Vcompression/Vsize_bitmap/Vhoriz_resol_pixel' . '/Vcompression/Vsize_bitmap/Vhoriz_resolution' .color/Voported $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['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;

 $PALETTE = array();
 if ($BMP['colors']  {
 $PALETTE = unpack('V'.$BMP['colors'], fread( $f1,$BMP['colors']*4));
 }

 $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  if ( $BMP[ 'bits_per_pixel'] == 32 ){
 $COLOR = unpack( "V", substr( $IMG, $P, 3 ) );
 $B = ord(substr($IMG, $P,1 ));
 $G = ord(substr($IMG, $P 1,1));
 $R = ord(substr($IMG, $P 2,1));
 $color = imagecolorexact( $res, $R, $G, $B );
 if ( $color == -1 )
 $color = imagecolorallocate( $res, $R, $G, $B );
 $COLOR[0] = $R*256*256 $G*256 $B;
 $COLOR[1] = $color;
 } elseif ( $BMP['bits_per_pixel'] == 24 ) {
 $COLOR = unpack( "V", substr( $IMG, $P, 3 ) . $VIDE );
 } elseif ( $BMP['bits_per_pixel'] == 16 ){
 $ COLOR = unpack("v",substr($IMG,$P,2));
 $blue = (($COLOR[1] & 0x001f)  $green = (( $COLOR[1] & 0x03e0) >> 2) 7;
 $red = (($COLOR[1] & 0xfc00) >> 7) 7;
 $COLOR[1] = $red * 65536 $ green * 256 $blue;
 } 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'];
	}
	fclose( $f1 );

	return $res;
}