（実践）PHPでサムネイルを生成する例

<?php

    function getCropper($source_path,$NewImagePath, $target_width, $target_height)
    {
        $source_info   = getimagesize($source_path);
        $source_width  = $source_info[0];
        $source_height = $source_info[1];
        $source_mime   = $source_info[&#39;mime&#39;];
        $source_ratio  = $source_height / $source_width;
        $target_ratio  = $target_height / $target_width;

        // 源图过高
        if ($source_ratio > $target_ratio)
        {
            $cropped_width  = $source_width;
            $cropped_height = $source_width * $target_ratio;
            $source_x = 0;
            $source_y = ($source_height - $cropped_height) / 2;
        }
        // 源图过宽
        elseif ($source_ratio < $target_ratio)
        {
            $cropped_width  = $source_height / $target_ratio;
            $cropped_height = $source_height;
            $source_x = ($source_width - $cropped_width) / 2;
            $source_y = 0;
        }
        // 源图适中
        else
        {
            $cropped_width  = $source_width;
            $cropped_height = $source_height;
            $source_x = 0;
            $source_y = 0;
        }

        switch ($source_mime)
        {
            case &#39;image/gif&#39;:
                $source_image = imagecreatefromgif($source_path);
                break;

            case &#39;image/jpeg&#39;:
                $source_image = imagecreatefromjpeg($source_path);
                break;

            case &#39;image/png&#39;:
                $source_image = imagecreatefrompng($source_path);
                break;

            default:
                return false;
                break;
        }

        $target_image  = imagecreatetruecolor($target_width, $target_height);
        $cropped_image = imagecreatetruecolor($cropped_width, $cropped_height);

        // 图片裁剪
        imagecopy($cropped_image, $source_image, 0, 0, $source_x, $source_y, $cropped_width, $cropped_height);
        // 图片缩放
        imagecopyresampled($target_image, $cropped_image, 0, 0, 0, 0, $target_width, $target_height, $cropped_width, $cropped_height);


        header(&#39;Content-Type: image/jpeg&#39;);
        imagejpeg($target_image,$NewImagePath,100);
        imagedestroy($source_image);
        imagedestroy($target_image);
        imagedestroy($cropped_image);
        
    }

<?php
//生成缩略图，填充白边
    function getCrops($src_path,$NewImagePath,$width,$height){

        //源图对象
        $src_image = imagecreatefromstring(file_get_contents($src_path));
        $source_info   = getimagesize($src_path);
        $source_mime   = $source_info[&#39;mime&#39;];
        $src_width = imagesx($src_image);
        $src_height = imagesy($src_image);

        switch ($source_mime)
        {
            case &#39;image/gif&#39;:
                $src_image = imagecreatefromgif($src_path);
                break;

            case &#39;image/jpeg&#39;:
                $src_image = imagecreatefromjpeg($src_path);
                break;

            case &#39;image/png&#39;:
                $src_image = imagecreatefrompng($src_path);
                break;

            default:
                return false;
                break;
        }


        //生成等比例的缩略图
        //$tmp_image_width = 0;
        //$tmp_image_height = 0;
        if ($src_width / $src_height >= $width / $height) {

            $tmp_image_width = $width;
            $tmp_image_height = round($tmp_image_width * $src_height / $src_width);

        } else {

            $tmp_image_height = $height;
            $tmp_image_width = round($tmp_image_height * $src_width / $src_height);
        }

        $tmpImage = imagecreatetruecolor($tmp_image_width, $tmp_image_height);
        imagecopyresampled($tmpImage, $src_image, 0, 0, 0, 0, $tmp_image_width, $tmp_image_height, $src_width, $src_height);

        //添加白边
        $final_image = imagecreatetruecolor($width, $height);
        $color = imagecolorallocate($final_image, 255, 255, 255);
        imagefill($final_image, 0, 0, $color);
        $x = round(($width - $tmp_image_width) / 2);
        $y = round(($height - $tmp_image_height) / 2);
        imagecopy($final_image, $tmpImage, $x, $y, 0, 0, $tmp_image_width, $tmp_image_height);

        //输出图片
        header(&#39;Content-Type: image/jpeg&#39;);
        imagejpeg($final_image,$NewImagePath,100);
        imagedestroy($src_image);
        imagedestroy($final_image);


    }