无法创建png

my code isnt working for png it works well. everything installed on machine. GD + jpglib

my code in fuctions.php

if ($_GET['_create_precut_images']==1) {
        $test_file = '/home/x/public_html/wp-content/themes/template/images/subpages-bg.jpg';
        //var_dump(file_exists($test_file));
        //var_dump(fopen($test_file,'r'));
        $orig_im = imagecreatefromjpeg($test_file);
        imagejpeg(
                $orig_im,
                "/home/x/public_html/work_files/rTDKYTzgFPdjuFeuvHrJg9QbcLdREM/test.jpg"
        );


    if (0) create_precut_images(
            '/home/x/public_html/work_files/rTDKYTzgFPdjuFeuvHrJg9QbcLdREM/full.png',
            '/home/x/public_html/work_files/rTDKYTzgFPdjuFeuvHrJg9QbcLdREM/thumb.png',
            '/home/x/public_html/work_files/rTDKYTzgFPdjuFeuvHrJg9QbcLdREM/precut.jpg'
            ,491
    );

is there any problem with the code? or maybe a server-side? i tried changing php.ini and set max limit didnt work well.