20 php GD库有的图片压缩后更大了？

$newImage = imagecreatetruecolor($newWidth, $newHeight);
$source = imagecreatefrompng($imagePath);
imagecopyresampled($newImage, $source, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);
imagepng($newImage, $imagePath, 6);

php7 GD库，有的图片，为啥压缩后变大了 原图100k变300k,300k变700k
完整源码

namespace app\common\model;

use think\Model;

class Attachment extends Model
{
}
$attachment = new Attachment();
$attachment->data(array_filter($params));
$attachment->save();

\think\Hook::listen("upload_after", $attachment);
$this->miniImg($attachment);


public function miniImg($attachment, $maxWidth = 800, $maxHeight = 600, $aspectRatioThreshold = 2) {
        if (!stristr($attachment->mimetype, 'image')) {
            return;
        }

        $imagePath = ltrim($attachment->url, '/');
        if (!file_exists($imagePath)) {
            return;
        }

        $fileSize = filesize($imagePath);
        if ($fileSize < 300 * 1024) {
            return; // 如果文件小于300KB，则不处理
        }

        list($width, $height, $type) = getimagesize($imagePath);
        $newWidth = $width;![]
        $newHeight = $height;

        // 如果宽度或高度超过最大值，则进行特殊处理
        if ($width > $maxWidth || $height > $maxHeight) {
            $ratio = max($width / $maxWidth, $height / $maxHeight);
            $newWidth = ceil($width / $ratio);
            $newHeight = ceil($height / $ratio);

            if ($width / $height > $aspectRatioThreshold) {
                $newHeight = ceil($newWidth / $aspectRatioThreshold);
            } elseif ($height / $width > $aspectRatioThreshold) {
                $newWidth = ceil($newHeight * $aspectRatioThreshold);
            }
        }

        $newImage = imagecreatetruecolor($newWidth, $newHeight);
        switch ($type) {
            case IMAGETYPE_JPEG:
                $source = imagecreatefromjpeg($imagePath);
                break;
            case IMAGETYPE_PNG:
                $source = imagecreatefrompng($imagePath);
                break;
            case IMAGETYPE_GIF:
                $source = imagecreatefromgif($imagePath);
                break;
            case IMAGETYPE_WEBP:
                $source = imagecreatefromwebp($imagePath);
                break;
            default:
                return; // 不支持的图片类型
        }

        imagecopyresampled($newImage, $source, 0, 0, 0, 0, $newWidth, $newHeight, $width, $height);
        switch ($type) {
            case IMAGETYPE_JPEG:
                imagejpeg($newImage, $imagePath, 60);
                break;
            case IMAGETYPE_PNG:
                imagepng($newImage, $imagePath, 6);
                break;
            case IMAGETYPE_GIF:
                imagegif($newImage, $imagePath);
                break;
            case IMAGETYPE_WEBP:
                imagewebp($newImage, $imagePath, 60);
                break;
        }

        imagedestroy($source);
        imagedestroy($newImage);
    }