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:

复制代码 代码如下:<?php

/*

* http://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:

复制代码 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。