PHP实现图片等比例缩略图：类与自定义函数两种方案

$resizeimage = new resizeimage("./shawn.jpg", "200", "100", "0", "../pic/shawnsun.jpg");
// 实例化后会立即执行生成操作

<?php
class resizeimage{
    public $type, $width, $height;
    public $resize_width, $resize_height;
    public $cut, $srcimg, $dstimg, $im;

    function resizeimage($img, $wid, $hei, $c, $dstpath){
        $this->srcimg = $img;
        $this->resize_width = $wid;
        $this->resize_height = $hei;
        $this->cut = $c;
        
        // 识别图片类型 (jpg/gif/png)
        $this->type = strtolower(substr(strrchr($this->srcimg,"."),1));
        
        // 初始化资源
        $this->initi_img();
        $this->dst_img($dstpath);
        
        $this->width = imagesx($this->im);
        $this->height = imagesy($this->im);
        
        // 执行生成
        $this->newimg();
        ImageDestroy ($this->im);
    }

    function initi_img(){
        if($this->type=="jpg") $this->im = imagecreatefromjpeg($this->srcimg);
        elseif($this->type=="gif") $this->im = imagecreatefromgif($this->srcimg);
        elseif($this->type=="png") $this->im = imagecreatefrompng($this->srcimg);
    }

    function dst_img($dstpath){
        $this->dstimg = $dstpath;
    }

    function newimg(){
        $resize_ratio = ($this->resize_width)/($this->resize_height);
        $ratio = ($this->width)/($this->height);
        
        $newimg = imagecreatetruecolor($this->resize_width, $this->resize_height);

        if($this->cut == "1") {
            // 裁切逻辑
            if($ratio >= $resize_ratio) {
                imagecopyresampled($newimg, $this->im, 0, 0, 0, 0,
                    $this->resize_width, $this->resize_height,
                    (($this->height)*$resize_ratio), $this->height);
            } else {
                imagecopyresampled($newimg, $this->im, 0, 0, 0, 0,
                    $this->resize_width, $this->resize_height,
                    $this->width, (($this->width)/$resize_ratio));
            }
        } else {
            // 等比缩放逻辑
            if($ratio >= $resize_ratio) {
                $final_w = $this->resize_width;
                $final_h = ($this->resize_width)/$ratio;
                $newimg = imagecreatetruecolor($final_w, $final_h);
                imagecopyresampled($newimg, $this->im, 0, 0, 0, 0,
                    $final_w, $final_h, $this->width, $this->height);
            } else {
                $final_w = ($this->resize_height)*$ratio;
                $final_h = $this->resize_height;
                $newimg = imagecreatetruecolor($final_w, $final_h);
                imagecopyresampled($newimg, $this->im, 0, 0, 0, 0,
                    $final_w, $final_h, $this->width, $this->height);
            }
        }
        ImageJpeg ($newimg, $this->dstimg);
    }
}
?>

thumbs('shawn.jpg', 'shawnsun.jpg', 100, 100);

<?php
function thumbs($FileName, $SaveTo, $SetW, $SetH){
    $IMGInfo = getimagesize($FileName);
    if(!$IMGInfo) return false;
    
    // 根据MIME类型加载图像
    if(in_array($IMGInfo['mime'], ['image/pjpeg', 'image/jpeg'])) {
        $ThisPhoto = imagecreatefromjpeg($FileName);
    } elseif(in_array($IMGInfo['mime'], ['image/x-png', 'image/png'])) {
        $ThisPhoto = imagecreatefrompng($FileName);
    } elseif($IMGInfo['mime'] == "image/gif") {
        $ThisPhoto = imagecreatefromgif($FileName);
    } else {
        return false;
    }
    
    $width = $IMGInfo[0];
    $height = $IMGInfo[1];
    
    // 计算缩放比例，防止变形
    $scalc = max($width/$SetW, $height/$SetH);
    $nw = intval($width / $scalc);
    $nh = intval($height / $scalc);
    
    // 微调以适配整数像素边界（可选优化）
    if($SetW - $nw == 1) $nw = $SetW;
    if($SetH - $nh == 1) $nh = $SetH;
    
    // 确定最终画布偏移量，实现居中
    $px = ($SetW - $nw) / 2;
    $py = ($SetH - $nh) / 2;
    
    // 创建空白画布并填充
    $NewPhoto = imagecreatetruecolor($SetW, $SetH);
    // 实际绘制，保留透明通道需额外处理Alpha，此处默认背景
    imagecopyresized($NewPhoto, $ThisPhoto, $px, $py, 0, 0, $nw, $nh, $width, $height);
    
    // 输出JPEG格式
    ImageJpeg ($NewPhoto, $SaveTo);
    imagedestroy($ThisPhoto);
    imagedestroy($NewPhoto);
    return true;
}
?>