使用 PHP GD `imagecreatefromstring` 函数创建图像的问题

Question

I have a simple service that generates a PNG image of any text, using the parameters passed via a URL. One of the parameters is the text itself, the rest are things like 'font', 'color', 'font weight' etc.

An example of such a URL is: http://picselbocs.com/projects/cakemyface/text.php?params=Verdana%7C18%7Cbold%7Cnormal%7Ccenter%7C%23cc0000%7Cunderline&text=Hello%20world!

which generates the following PNG:

In another script, I'm using cURL to retrieve such a resource generated by this service, which I then convert to an image using imagecreatefromstring() , because I need to operate on it - things like rotating and scaling -, then to merge it with some other images. For this I use the following code:

function getImage($url){
            $ch = curl_init ($url);
            curl_setopt($ch, CURLOPT_HEADER, 0);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
            curl_setopt($ch, CURLOPT_BINARYTRANSFER,1);
            $resource = curl_exec($ch);
            curl_close ($ch);

            return $resource;
    }


    $url = "http://picselbocs.com/projects/cakemyface/text.php?params=Verdana%7C18%7Cbold%7Cnormal%7Ccenter%7C%23cc0000%7Cunderline&text=Hello%20world!";

    $string = getImage($url);
    $image = imagecreatefromstring($string);

    // Send the image to the client
    header("Content-type: image/png");
    header("Content-disposition: inline; filename=mytext.png");
    imagepng($image);
    imagedestroy($image);

This same code is available here , where you can see the output. The problem is that the code above outputs some strange PNG, where all the letters are filled rectangles, like in the example bellow:

Why does this happen and how can I solve it?

One other curious thing is that if I replace a URL to a text-image with, for instance, a link to a QR code generated with the Google Charts tool (eg QR code ), the result is what it's supposed to be...

Answer 1

After a little playing about I discovered the issue and the solution!

$image = imagecreatefromstring(file_get_contents('http://picselbocs.com/projects/cakemyface/text.php?params=Verdana|18|bold|normal|center|%23cc0000|underline&text=Hello%20world!'));
imagesavealpha($image, TRUE); // this is the fix
header("Content-Type: image/png");
imagepng($image);

The way I create my image is just a quick way without using curl, it seems the image needs it's alpha channels saving.