php实现高效获取图片尺寸的方法

本文实例讲述了php实现高效获取图片尺寸的方法。分享给大家供大家参考。具体分析如下：

php 获取图片尺寸的方法我们可以使用 getimagesize 获取图片尺寸，但是效率是很低的,首先需要获取整个的图片信息,然后再进行操作,下面的例子更科学算法更好,我们一起来看看吧.

方法可以用于快速获取图片尺寸信息,获取jpeg格式图片的尺寸信息,并且不需要下载读取整个图片,经测试这个函数不是对所有jpeg格式的图片都有效.

1.获取jpeg格式图片的尺寸信息,代码如下:

<?php
/*
* //www.jb51.net
*/
 
// retrieve jpeg width and height without downloading/reading entire image.
function getjpegsize($img_loc) {
    $handle = fopen($img_loc, "rb") or die("invalid file stream.");
    $new_block = null;
    if(!feof($handle)) {
        $new_block = fread($handle, 32);
        $i = 0;
        if($new_block[$i]=="xff" && $new_block[$i+1]=="xd8" && $new_block[$i+2]=="xff" && $new_block[$i+3]=="xe0") {
            $i += 4;
            if($new_block[$i+2]=="x4a" && $new_block[$i+3]=="x46" && $new_block[$i+4]=="x49" && $new_block[$i+5]=="x46" && $new_block[$i+6]=="x00") {
                
// read block size and skip ahead to begin cycling through blocks in search of sof marker
 
                $block_size = unpack("h*", $new_block[$i] . $new_block[$i+1]);
                $block_size = hexdec($block_size[1]);
                while(!feof($handle)) {
                    $i += $block_size;
                    $new_block .= fread($handle, $block_size);
                    if($new_block[$i]=="xff") {
                        
// new block detected, check for sof marker
 
                        $sof_marker = array("xc0", "xc1", "xc2", "xc3", "xc5", "xc6", "xc7", "xc8", "xc9", "xca", "xcb", "xcd", "xce", "xcf");
                        if(in_array($new_block[$i+1], $sof_marker)) {
                            
// sof marker detected. width and height information is contained in bytes 4-7 after this byte.
 
                            $size_data = $new_block[$i+2] . $new_block[$i+3] . $new_block[$i+4] . $new_block[$i+5] . $new_block[$i+6] . $new_block[$i+7] . $new_block[$i+8];
                            $unpacked = unpack("h*", $size_data);
                            $unpacked = $unpacked[1];
                            $height = hexdec($unpacked[6] . $unpacked[7] . $unpacked[8] . $unpacked[9]);
                            $width = hexdec($unpacked[10] . $unpacked[11] . $unpacked[12] . $unpacked[13]);
                            return array($width, $height);
                        } else {
                            
// skip block marker and read block size
 
                            $i += 2;
                            $block_size = unpack("h*", $new_block[$i] . $new_block[$i+1]);
                            $block_size = hexdec($block_size[1]);
                        }
                    } else {
                        return false;
                    }
                }
            }
        }
    }
    return false;
}
?>

2.实例代码如下:

$url='http://www.xxxx.com/images/1331189004_28093400.jpg';
$image_content = file_get_contents($url);
$image = imagecreatefromstring($image_content);
$width = imagesx($image);
$height = imagesy($image);
echo $width.'*'.$height."nr";

希望本文所述对大家的php程序设计有所帮助。