base64 encode PHP generated image without writing the image to disk - php

Question

I'm generating an image in PHP for use in a users avatar.
I start by hashing the username and then doing a hexdec() conversion on various substrings of the hash to build up a set of RGB colours.
//create image
$avatarImage = imagecreate(250, 250);
// first call to imagecolorallocate sets the background colour
$background = imagecolorallocate($avatarImage, hexdec(substr($hash, 0, 2)), hexdec(substr($hash, 2, 2)), hexdec(substr($hash, 4, 2)));
//write the image to a file
$imageFile = 'image.png';
imagepng($avatarImage, $imageFile);
//load file contents and base64 encode
$imageData = base64_encode(file_get_contents($imageFile));
//build $src dataURI.
$src = 'data: ' . mime_content_type($imageFile) . ';base64,' . $imageData;
Ideally I'd not use the intermediate step and would skip writing the image out onto disk, although I'm not sure how best to implement this?
I've tried passing $avatarImage directly to base64_encode() but that expects a string so doesn't work.
Any ideas?

Answer 1

You can imagepng to a variable:
//create image
$avatarImage = imagecreate(250, 250);
//whatever image manipulations you do
//write the image to a variable
ob_start();
imagepng($avatarImage);
$imagePng = ob_get_contents();
ob_end_clean();
//base64 encode
$imageData = base64_encode($imagePng);
//continue

Answer 2

You can use output buffering to capture the image data and then use it as desired:
ob_start ( ); // Start buffering
imagepng($avatarImage); // output image
$imageData = ob_get_contents ( ); // store image data
ob_end_clean ( ); // end and clear buffer
For convenience you could create a new function to handle image encoding:
function createBase64FromImageResource($imgResource) {
ob_start ( );
imagepng($imgResource);
$imgData = ob_get_contents ( );
ob_end_clean ( );
return base64_encode($imgData);
}