用保留质量的php调整图片大小

Posted 2023-02-25

【中文标题】用保留质量的php调整图片大小

【英文标题】：Resizing pictures with preserving quality php

【发布时间】：2012-09-03 13:02:48

【问题描述】：

我使用以下方法调整图像大小：

 private function newDim($maxHeight, $maxWidth, $height, $width) 

        if(($width / $height) >= ($maxWidth / $maxHeight))
                $nw = $maxWidth;
                $nh = $height * ($maxWidth / $width);
                $nx = round(abs($maxHeight - $nh) / 2);
                $ny = 0 ;
        else 
            // by height
                $nw = $width*($maxHeight/$height);
                $nh = $maxHeight;
                $nx = 0;
                $ny = round(abs($maxWidth - $nw) / 2); ;
        

        return array($nw,$nh,$nx,$ny);
    

之后我想保存这张图片。对于这种情况，我使用这种方法：

 public function upload($file_param_name) 
        $file_name = $_FILES[$file_param_name]['name'];
        $source_file_path = $_FILES[$file_param_name]['tmp_name'];
        $$this->ext = pathinfo($file_name, PATHINFO_EXTENSION);
        $ext = 'jpg';
        $this->ext = $ext;
        $ext =strtolower($ext);
        $new_file_name = $file_name."-".md5(uniqid(rand(), true));
        $this->image_hashname = $new_file_name;
        $target_path = $this->store_folder.basename($new_file_name);

        list($width,$height,$type)=getimagesize($source_file_path);

        switch ($type) 
            case 1:   //   gif -> jpg
                $src = imagecreatefromgif($source_file_path);
                break;
            case 2:   //   jpeg -> jpg
                $src = imagecreatefromjpeg($source_file_path);
                break;
            case 3:  //   png -> jpg
                $src = imagecreatefrompng($source_file_path);
                break;
        

        $th = 240;
        $tw = 240;

        list($nh,$nw,$nx,$ny) = $this->newDim($th, $tw, $height, $width);

        $tmp=imagecreatetruecolor($tw,$th);

        $white = imagecolorallocate($tmp, 255,255,255);
        imagefill($tmp, 0, 0, $white);

        imagecopyresized($tmp,$src,$ny,$nx,0,0,$nh,$nw,$width,$height);
        $thmbfile = $this->store_folder.basename($new_file_name."-thumb.".$ext);
        imagejpeg($tmp,$thmbfile,100);


        imagedestroy($src);
        imagedestroy($tmp);
    

当我保存尺寸为 300x300 到 240x240 的图像时，新图像的质量很差。我哪里错了？

图片：

旧：http://cbn-design.eu/imgs/original.jpg

新：http://cbn-design.eu/imgs/new.jpg

【问题讨论】：

你能用 ImageMagick 代替吗？看到这个问题：ImageMagick vs GD - which is faster, less resource intensive and produces better images?

【参考方案1】：

根据this answer，尝试使用imagecopyresampled() 而不是imagecopyresized()。