php如何bmp转png图片

问题：

php在线用tcpdf生成的pdf预览文件 无法显示bmp格式的图片

tcpdf的图片渲染依赖于gd库 gd库不支持image/x-ms-bmp格式的图片 虽然上传的图片后缀是png的 但实际上图片的原始格式是bmp的

解决办法： 

在上传的时候 检测到图片原始格式为bmp的 就进行转换格式为png后 再上传到服务器

代码：

读取上传的图片文件流的原始格式

<?php
/**
*获取真实文件扩展名
*/
function getrealextension(){
　　//获取上传文件信息
　　$file_info = $_FILES['file'];

　　//获取上传文件的临时文件名
　　$tmp_name = $file_info['tmp_name'];

　　//获取图片信息
　　$image_info = getimagesize($tmp_name);

　　//获取图片文件第一行的格式
　　$mime_type = $image_info['mime'];

　　//输出文件类型
　　return $mime_type;
}
?>

x-ms-bmp格式转bmp格式保存

<?php
/**
*bmp格式转png
*@param $bmp_path 文件流地址 
*/
function bmptopng($bmp_path){
   //加载BMP图片
   $bmp = imagecreatefrombmp($bmp_path);

   //创建一个空的PNG图片
   $png = imagecreatetruecolor(imagesx($bmp), imagesy($bmp));

  //将BMP转换为PNG
   imagecopy($png, $bmp, 0, 0, 0, 0, imagesx($bmp), 
   imagesy($bmp));

   //指定PNG图片文件路径
   $png_path = 'example.png';

   //将PNG保存到指定路径
   imagepng($png, $png_path);

   return $png_path; 
}
$bmp_path = $_FILES['file']['tmp_name'];
$real = getrealextension();

if($real == 'image/x-ms-bmp'){
 $tmp_png_path = bmptopng($bmp_path); 
}

?>

 注意事项：

  Call to undefined function ImageCreateFrombmp() 

解决办法：

    将以下代码放到公共函数文件中 （Common/Common/function.php）即可,以下是代码：

/**
 * BMP 创建函数
 * @author simon
 * @param string $filename path of bmp file
 * @example who use,who knows
 * @return resource of GD
 */
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'] != 19778 )
        return FALSE;

    $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;

    $PALETTE = array();
    if ( $BMP['colors'] < 16777216 ){
        $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 < $BMP['width'] ){
            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( "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'];
    }
    fclose( $f1 );

    return $res;
}