Resizing with GD outputs black images

Question

What can cause php gd to produce a black image after resizing? The following code always outputs a black image for every valid jpeg file.

Answer 1

Research

Just tried to reproduce your situation. Running your code with out-of-the-box PHP and Apache displays the following

The image “http://localhost/” cannot be displayed because it contains errors.

Although browser tells you that there were some errors, they cannot be seen because of the headers returned in response were of Content-Type: image/jpeg thus forcing browser to interpret it as an image. By removing the header and setting the following will output errors.

ini_set('error_reporting', E_ALL);
ini_set('display_errors', true);
...
//header('Content-Type: image/jpeg');
...

Answer

What can cause php gd to produce a black image after resizing?

Since the gd_info output proves that the GD extension is loaded, check if the filename (linux is caseSensitive) and permissions are correct. If Apache is running as www-data (group)

sudo chown :www-data test.jpg && sudo chmod 660 test.jpg 

Code improvement / solution

ini_set('error_reporting', E_ALL);
ini_set('display_errors', true);

if (extension_loaded('gd') && function_exists('gd_info'))
{
    $filename = 'test.jpg';

    if (file_exists($filename) && is_readable($filename))
    {
        $percent = 0.5;

        header('Content-Type: image/jpeg');

        list($width, $height) = getimagesize($filename);
        $newwidth = $width * $percent;
        $newheight = $height * $percent;

        $thumb = imagecreatetruecolor($newwidth, $newheight);
        $source = imagecreatefromjpeg($filename);

        imagecopyresized($thumb, $source, 0, 0, 0, 0, $newwidth, $newheight, $width, $height);

        imagejpeg($thumb);
        imagedestroy($thumb);
    }
    else
    {
        trigger_error('File or permission problems');
    }
}
else
{
    trigger_error('GD extension not loaded');
}

Comments

This should be used as a temporary solution (development environment). IMHO, the errors should be handled by a central error handler, display_errors should be false in production. Also, the errors (in this case there would be Fatal error) are logged by default - check the logs for more (the frequent, the better). Also, on linux (with apt) the one-liner will install GD on your system:

sudo apt-get update && sudo apt-get install php5-gd && sudo /etc/init.d/apache2 restart