PHP实现图片压缩

/**
* 生成图片
* @param string $im 源图片路径
* @param string $dest 目标图片路径
* @param int $maxwidth 生成图片宽
* @param int $maxheight 生成图片高
*/
function resizeImage($im, $dest, $maxwidth, $maxheight) {
$img = getimagesize($im);
switch ($img[2]) {
case 1:
$im = @imagecreatefromgif($im);
break;
case 2:
$im = @imagecreatefromjpeg($im);
break;
case 3:
$im = @imagecreatefrompng($im);
break;
}
$pic_width = imagesx($im);
$pic_height = imagesy($im);
$resizewidth_tag = false;
$resizeheight_tag = false;
if (($maxwidth && $pic_width   $maxwidth) || ($maxheight && $pic_height   $maxheight)) {
if ($maxwidth && $pic_width   $maxwidth) {
$widthratio = $maxwidth / $pic_width;
$resizewidth_tag = true;
}
if ($maxheight && $pic_height   $maxheight) {
$heightratio = $maxheight / $pic_height;
$resizeheight_tag = true;
}
if ($resizewidth_tag && $resizeheight_tag) {
if ($widthratio < $heightratio)
$ratio = $widthratio;
else
$ratio = $heightratio;
}
if ($resizewidth_tag && !$resizeheight_tag)
$ratio = $widthratio;
if ($resizeheight_tag && !$resizewidth_tag)
$ratio = $heightratio;
$newwidth = $pic_width * $ratio;
$newheight = $pic_height * $ratio;
if (function_exists("imagecopyresampled")) {
$newim = imagecreatetruecolor($newwidth, $newheight);
imagecopyresampled($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $pic_width, $pic_height);
} else {
$newim = imagecreate($newwidth, $newheight);
imagecopyresized($newim, $im, 0, 0, 0, 0, $newwidth, $newheight, $pic_width, $pic_height);
}
imagejpeg($newim, $dest);
imagedestroy($newim);
} else {
imagejpeg($im, $dest);
}
}
/**
* 图片压缩处理
* @param string $sFile 源图片路径
* @param int $iWidth 自定义图片宽度
* @param int $iHeight 自定义图片高度
* @return string 压缩后的图片路径
*/
function getThumb($sFile,$iWidth,$iHeight){
//图片公共路径
$public_path = '';
//判断该图片是否存在
if(!file_exists($public_path.$sFile)) return $sFile;
//判断图片格式(图片文件后缀)
$extend = explode("." , $sFile);
$attach_fileext = strtolower($extend[count($extend) - 1]);
if (!in_array($attach_fileext, array('jpg','png','jpeg'))){
return '';
}
//压缩图片文件名称
$sFileNameS = str_replace(".".$attach_fileext, "_".$iWidth.'_'.$iHeight.'.'.$attach_fileext, $sFile);
//判断是否已压缩图片，若是则返回压缩图片路径
if(file_exists($public_path.$sFileNameS)){
return $sFileNameS;
}
//生成压缩图片，并存储到原图同路径下
resizeImage($public_path.$sFile, $public_path.$sFileNameS, $iWidth, $iHeight);
if(!file_exists($public_path.$sFileNameS)){
return $sFile;
}
return $sFileNameS;
}

//原图 img/img.jpg
//生成压缩图 img/img_300_300.jpg
getThumb('img/img.jpg',300,300);