php - 更好质量的缩略图

Question

我有一个脚本可以成功创建缩略图，但它们呈现的质量很低。我可以在脚本中更改哪些内容以提高缩略图的质量？

function createThumbnail($filename) {

    $final_width_of_image = 200;
    $path_to_image_directory = 'images/fullsized/';
    $path_to_thumbs_directory = 'images/thumbs/';

    if(preg_match('/[.](jpg)$/', $filename)) {
        $im = imagecreatefromjpeg($path_to_image_directory . $filename);
    } else if (preg_match('/[.](gif)$/', $filename)) {
        $im = imagecreatefromgif($path_to_image_directory . $filename);
    } else if (preg_match('/[.](png)$/', $filename)) {
        $im = imagecreatefrompng($path_to_image_directory . $filename);
    }

    $ox = imagesx($im);
    $oy = imagesy($im);

    $nx = $final_width_of_image;
    $ny = floor($oy * ($final_width_of_image / $ox));

    $nm = imagecreatetruecolor($nx, $ny);

    imagecopyresized($nm, $im, 0,0,0,0,$nx,$ny,$ox,$oy);

    if(!file_exists($path_to_thumbs_directory)) {
      if(!mkdir($path_to_thumbs_directory)) {
           die("There was a problem. Please try again!");
      }
       }

    imagejpeg($nm, $path_to_thumbs_directory . $filename);
    $tn = '<img src="' . $path_to_thumbs_directory . $filename . '" alt="image" />';
    $tn .= '<br />Congratulations. Your file has been successfully uploaded, and a thumbnail has been created.';
    echo $tn;   
}

Answer 1

我可以用这段代码提出的唯一建议是:

• 增加 $final_width_of_image 以制作更大的缩略图。
• 将第三个quality参数添加到imagejpeg；根据 the PHP manual ，它的范围从 0 到 100，其中 100 是最好的质量。
• 不要为您的缩略图使用 JPEG。
• 使用imagecopyresampled获得更好的像素插值算法。