/**
     * 处理圆角图片
     *
     * @param string  $imgpath 源图片路径
     * @param integer $radius  圆角半径长度默认为15,处理成圆型
     *
     * @return [type]           [description]
     */
    public function radius_img($imgpath = '', $radius = 15) {
        $ext     = pathinfo($imgpath);
        $src_img = null;
        switch ($ext['extension']) {
            case 'jpg':
                $src_img = imagecreatefromjpeg($imgpath);
                break;
            case 'png':
                $src_img = imagecreatefrompng($imgpath);
                break;
        }
        $wh = getimagesize($imgpath);
        $w  = $wh[0];
        $h  = $wh[1];
        // $radius = $radius == 0 ? (min($w, $h) / 2) : $radius;
        $img = imagecreatetruecolor($w, $h);
        //这一句一定要有
        imagesavealpha($img, true);
        //拾取一个完全透明的颜色,最后一个参数127为全透明
        $bg = imagecolorallocatealpha($img, 255, 255, 255, 127);
        imagefill($img, 0, 0, $bg);
        $r = $radius; //圆 角半径
        for ($x = 0; $x < $w; $x++) {
            for ($y = 0; $y < $h; $y++) {
                $rgbColor = imagecolorat($src_img, $x, $y);
                if (($x >= $radius && $x <= ($w - $radius)) || ($y >= $radius && $y <= ($h - $radius))) {
                    //不在四角的范围内,直接画
                    imagesetpixel($img, $x, $y, $rgbColor);
                } else {
                    //在四角的范围内选择画
                    //上左
                    $y_x = $r; //圆心X坐标
                    $y_y = $r; //圆心Y坐标
                    if (((($x - $y_x) * ($x - $y_x) + ($y - $y_y) * ($y - $y_y)) <= ($r * $r))) {
                        imagesetpixel($img, $x, $y, $rgbColor);
                    }
                    //上右
                    $y_x = $w - $r; //圆心X坐标
                    $y_y = $r; //圆心Y坐标
                    if (((($x - $y_x) * ($x - $y_x) + ($y - $y_y) * ($y - $y_y)) <= ($r * $r))) {
                        imagesetpixel($img, $x, $y, $rgbColor);
                    }
                    //下左
                    $y_x = $r; //圆心X坐标
                    $y_y = $h - $r; //圆心Y坐标
                    if (((($x - $y_x) * ($x - $y_x) + ($y - $y_y) * ($y - $y_y)) <= ($r * $r))) {
                        imagesetpixel($img, $x, $y, $rgbColor);
                    }
                    //下右
                    $y_x = $w - $r; //圆心X坐标
                    $y_y = $h - $r; //圆心Y坐标
                    if (((($x - $y_x) * ($x - $y_x) + ($y - $y_y) * ($y - $y_y)) <= ($r * $r))) {
                        imagesetpixel($img, $x, $y, $rgbColor);
                    }
                }
            }
        }
        return $img;
    }

或者

/**
     * radius_img 图片处理为圆形
     *
     * @param string $imgpath
     *
     */
    public function radius_img($imgpath = '') {
        $ext     = pathinfo($imgpath);
        $src_img = null;
        switch ($ext['extension']) {
            case 'jpg':
                $src_img = imagecreatefromjpeg($imgpath);
                break;
            case 'png':
                $src_img = imagecreatefrompng($imgpath);
                break;
        }
        $wh  = getimagesize($imgpath);
        $w   = $wh[0];
        $h   = $wh[1];
        $w   = min($w, $h);
        $h   = $w;
        $img = imagecreatetruecolor($w, $h);
        //这一句一定要有
        imagesavealpha($img, true);
        //拾取一个完全透明的颜色,最后一个参数127为全透明
        $bg = imagecolorallocatealpha($img, 255, 255, 255, 127);
        imagefill($img, 0, 0, $bg);
        $r = $w / 2; //圆半径
        // $y_x = $r; //圆心X坐标
        // $y_y = $r; //圆心Y坐标
        for ($x = 0; $x < $w; $x++) {
            for ($y = 0; $y < $h; $y++) {
                $rgbColor = imagecolorat($src_img, $x, $y);
                if (((($x - $r) * ($x - $r) + ($y - $r) * ($y - $r)) < ($r * $r))) {
                    imagesetpixel($img, $x, $y, $rgbColor);
                }
            }
        }
        return $img;
    }