/**

* 等比例生成缩略图

* @param $imgSrc

* @param $resize_width

* @param $resize_height

* @param $isCut

* @author james.ou 2011-11-1

*/

public function reSizeImg($imgSrc, $resize_width, $resize_height, $isCut = false) {

//图片的类型

$type = substr(strrchr($imgSrc, "."), 1);

//初始化图象

if ($type == "jpg") {

$im = imagecreatefromjpeg($imgSrc);

}

if ($type == "gif") {

$im = imagecreatefromgif($imgSrc);

}

if ($type == "png") {

$im = imagecreatefrompng($imgSrc);

}

//目标图象地址

$full_length = strlen($imgSrc);

$type_length = strlen($type);

$name_length = $full_length - $type_length;

$name = substr($imgSrc, 0, $name_length - 1);

$dstimg = $name . "_s." . $type;

$width = imagesx($im);

$height = imagesy($im);

//生成图象

//改变后的图象的比例

$resize_ratio = ($resize_width) / ($resize_height);

//实际图象的比例

$ratio = ($width) / ($height);

if (($isCut) == 1) { //裁图

if ($ratio >= $resize_ratio) { //高度优先

$newimg = imagecreatetruecolor($resize_width, $resize_height);

imagecopyresampled($newimg, $im, 0, 0, 0, 0, $resize_width, $resize_height, (($height) * $resize_ratio), $height);

ImageJpeg($newimg, $dstimg);

}

if ($ratio < $resize_ratio) { //宽度优先

$newimg = imagecreatetruecolor($resize_width, $resize_height);

imagecopyresampled($newimg, $im, 0, 0, 0, 0, $resize_width, $resize_height, $width, (($width) / $resize_ratio));

ImageJpeg($newimg, $dstimg);

}

} else { //不裁图

if ($ratio >= $resize_ratio) {

$newimg = imagecreatetruecolor($resize_width, ($resize_width) / $ratio);

imagecopyresampled($newimg, $im, 0, 0, 0, 0, $resize_width, ($resize_width) / $ratio, $width, $height);

ImageJpeg($newimg, $dstimg);

}

if ($ratio < $resize_ratio) {

$newimg = imagecreatetruecolor(($resize_height) * $ratio, $resize_height);

imagecopyresampled($newimg, $im, 0, 0, 0, 0, ($resize_height) * $ratio, $resize_height, $width, $height);

ImageJpeg($newimg, $dstimg);

}

}

ImageDestroy($im);

}

原文：http://www.cnblogs.com/blog-dyn/p/7127799.html