save image stream to laravel

In my Laravel controller I'm attempting to take a string of image data, convert it to a png then save it to storage using put:

$image_string = $request->get('image_string', false);
$filename = 'temp_image';

if ($image_string) {
    $resource = imagecreatefromstring($image_string);
    Log::debug("Storing image");
    if ($resource !== false) {
        Storage::put('public/' . $filename . '.png', imagepng($resource));
    } else {
        Log::error("Failed to get resource from string");
    }
}

If I break out just the imagecreatefromstring($image_string) and imagepng($resource) parts, the file is created as expected. But somewhere in the Storage::put the image is either corrupted or lost, because while an image with the right filename and extension exists, it has no data and appears as a black box when viewed.

Is there a different way I need to handle the image store routine?

via Chebli Mohamed