GD缩略图无法在较大的文件大小上运行

Question

I am using GD Thumbnails in order to create and store thumbnails of uploaded images. Now it all works fine when small image sizes are used, but when the files start to get bigger, say around 3MB, the thumbnails are not created.

The limit on my file upload is 4MB, and the actual image itself is uploaded, it's just that the thumbnail isn't created.

I'm not very familiar with the script so I'm not really sure why it's not working. It may also be worth noting that the thumbnails (when they are created) are uploading to two different directories, but this may be something I have missed out along the way.

Any ideas would be much appreciated.

<?php 
$imagefolder='images';
$thumbsfolder='thumbs';
$pics=directory($imagefolder,"jpg,JPG,JPEG,jpeg,png,PNG");
$pics=ditchtn($pics,"tn_");
if ($pics[0]!="")
{
    foreach ($pics as $p)
    {
        createthumb($p,"tn_".$p,182,182);
    }
}

/*
    Function ditchtn($arr,$thumbname)
    filters out thumbnails
*/
function ditchtn($arr,$thumbname)
{
    foreach ($arr as $item)
    {
        if (!preg_match("/^".$thumbname."/",$item)){$tmparr[]=$item;}
    }
    return $tmparr;
}

/*
    Function createthumb($name,$filename,$new_w,$new_h)
    creates a resized image
    variables:
    $name       Original filename
    $filename   Filename of the resized image
    $new_w      width of resized image
    $new_h      height of resized image
*/  
function createthumb($name,$filename,$new_w,$new_h)
{
    $system=explode(".",$name);
    if (preg_match("/jpg|jpeg/",$system[1])){$src_img=imagecreatefromjpeg($name);}
    if (preg_match("/png/",$system[1])){$src_img=imagecreatefrompng($name);}
    $old_x=imageSX($src_img);
    $old_y=imageSY($src_img);
    if ($old_x > $old_y) 
    {
        $thumb_w=$new_w;
        $thumb_h=$old_y*($new_h/$old_x);
    }
    if ($old_x < $old_y) 
    {
        $thumb_w=$old_x*($new_w/$old_y);
        $thumb_h=$new_h;
    }
    if ($old_x == $old_y) 
    {
        $thumb_w=$new_w;
        $thumb_h=$new_h;
    }
    $dst_img=ImageCreateTrueColor($thumb_w,$thumb_h);
    imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y); 
    if (preg_match("/png/",$system[1]))
    {
        imagepng($dst_img,$filename); 
    } else {
        imagejpeg($dst_img,$filename); 
    }
    imagedestroy($dst_img); 
    imagedestroy($src_img); 
}

/*
        Function directory($directory,$filters)
        reads the content of $directory, takes the files that apply to $filter 
        and returns an array of the filenames.
        You can specify which files to read, for example
        $files = directory(".","jpg,gif");
                gets all jpg and gif files in this directory.
        $files = directory(".","all");
                gets all files.
*/
function directory($dir,$filters)
{
    $handle=opendir($dir);
    $files=array();
    if ($filters == "all"){while(($file = readdir($handle))!==false){$files[] = $file;}}
    if ($filters != "all")
    {
        $filters=explode(",",$filters);
        while (($file = readdir($handle))!==false)
        {
            for ($f=0;$f<sizeof($filters);$f++):
                $system=explode(".",$file);
                if ($system[1] == $filters[$f]){$files[] = $file;}
            endfor;
        }
    }
    closedir($handle);
    return $files;
}
?>