[PHP知识库]PHP压缩图片

/**
 * 图片压缩处理
 * @param string $oldImg 源图片路径
 * @param int $width 自定义图片宽度
 * @param int $height 自定义图片高度
 * @return string 压缩后的图片路径
 */
function getThumb($oldImg,$width = 0,$height = 0){
    //判断该图片是否存在
    if(!file_exists($oldImg)){
        return false;
    }
    //判断图片格式(图片文件后缀)
    $pathArr = pathinfo($oldImg);
    $extend = $pathArr['extension'];
    if(!in_array($extend,['jpg','png','jpeg'])){
        return false;
    }
    //未设置宽高 则以原尺寸压缩
    $oldImgInfo = getimagesize($oldImg);
    if(!$width){
        $width = $oldImgInfo[0];
    }
    if(!$height){
        $height = $oldImgInfo[1];
    }
    //压缩图片文件名称
    $newImg = str_replace('.'.$extend, '_thumb_'.$width.'_'.$height.'.'.$extend, $oldImg);
    //判断是否已压缩图片，若是则返回压缩图片路径
    if(file_exists($newImg)){
        return $newImg;
    }
    //生成压缩图片，并存储到原图同路径下
    resizeImage($oldImg, $newImg, $width, $height);
    if(!file_exists($newImg)){
        return $oldImg;
    }
    return $newImg;
}

/**
 * 生成图片
 * @param string $oldImgPath 源图片路径
 * @param string $newImgPath 目标图片路径
 * @param int $width 生成图片宽
 * @param int $height 生成图片高
 */
function resizeImage($oldImgPath, $newImgPath, $width, $height) {
    $img = getimagesize($oldImgPath);
    switch ($img[2]) {
        case 1:
            $resource = @imagecreatefromgif($oldImgPath);
            break;
        case 2:
            $resource = @imagecreatefromjpeg($oldImgPath);
            break;
        case 3:
            $resource = @imagecreatefrompng($oldImgPath);
            break;
        default:
            $resource = @imagecreatefrompng($oldImgPath);
            break;
    }
    //原图的宽
    $pic_width = imagesx($resource);
    //原图的高
    $pic_height = imagesy($resource);
    //判断是否压缩
    $resize_width_tag = $resize_height_tag = false;
    //默认压缩率1，即等尺寸压缩
    $width_ratio = $height_ratio = 1;
    if(($width && $pic_width > $width) || ($height && $pic_height > $height)){
        //宽度是否压缩
        if($width && $pic_width > $width){
            $width_ratio = $width / $pic_width;
            $resize_width_tag = true;
        }
        //高度是否压缩
        if($height && $pic_height > $height){
            $height_ratio = $height / $pic_height;
            $resize_height_tag = true;
        }
        //选择压缩率
        if($resize_width_tag && $resize_height_tag){
            if ($width_ratio < $height_ratio){
                $ratio = $width_ratio;
            } else{
                $ratio = $height_ratio;
            }
        }elseif ($resize_width_tag && !$resize_height_tag){
            $ratio = $width_ratio;
        }elseif ($resize_height_tag && !$resize_width_tag){
            $ratio = $height_ratio;
        }else{
            $ratio = 1;
        }
        $new_width = $pic_width * $ratio;
        $new_height = $pic_height * $ratio;
        if(function_exists("imagecopyresampled")){
            $newim = imagecreatetruecolor($new_width, $new_height);
            imagecopyresampled($newim, $resource, 0, 0, 0, 0, $new_width, $new_height, $pic_width, $pic_height);
        }else{
            $newim = imagecreate($new_width, $new_height);
            imagecopyresized($newim, $resource, 0, 0, 0, 0, $new_width, $new_height, $pic_width, $pic_height);
        }
        imagejpeg($newim, $newImgPath);
        imagedestroy($newim);
    } else {
        imagejpeg($resource, $newImgPath);
    }
}