php - Resizing base64 Images

Question

I have multiple Images - saved as Base64 Strings and now i want to resize these images to get thumbnails of them...

Best would be using Javascript (Node-Server) to resize them, but it would be possible to resize them with php, too.

Thanks in advance

Answer 1

I agree to the method from Jon Hanna: Do Parsing the Base64code then load it to GD Image before Resample. However to get it back as data it is not as easy as I though. On php in GAE it will need to enable output buffering by setting output_buffering = "On" in php.ini file.

Here I explain the step in detail.

This doc is taken as reference to Create Image Resource using the Parsing of Base64code: http://php.net/manual/en/function.imagecreatefromstring.php

// Create image resource from Base64code
$data64 = 'iVBORw0KGgoAAAANSUhEUgAAABwAAAASCAMAAAB/2U7WAAAABl'
        . 'BMVEUAAAD///+l2Z/dAAAASUlEQVR4XqWQUQoAIAxC2/0vXZDr'
        . 'EX4IJTRkb7lobNUStXsB0jIXIAMSsQnWlsV+wULF4Avk9fLq2r'
        . '8a5HSE35Q3eO2XP1A1wQkZSgETvDtKdQAAAABJRU5ErkJggg==';
$image = imagecreatefromstring(base64_decode($data64));

This is an image resource which can be directly put to the Resample function: http://php.net/manual/en/function.imagecopyresampled.php

// Resample
$image_p = imagecreatetruecolor($new_w, $new_h);
imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_w, $new_h, $org_w, $org_h);

The result is also an image resource. To get it as a data we need Buffering.
See how to create a base64encoded string from image resource

// Buffering
ob_start();
imagepng($image_p);
$data = ob_get_contents();
ob_end_clean();

Using doc below I set a GCS bucket on my project as a website so I can Store & Display it directly: https://cloud.google.com/storage/docs/website-configuration#tips

//Store & Display
$context = stream_context_create([
   'gs' =>[
        'acl'=> 'public-read', 
        'Content-Type' => 'image/jpeg', 
        'enable_cache' => true, 
        'enable_optimistic_cache' => true,
        'read_cache_expiry_seconds' => 300,
    ]
]);
file_put_contents("gs://mybucket/resample/image.jpeg", $data, false, $context); 
header("Location: http://mybucket/resample/image.jpeg");