CB

Currently Imagine will make a copy of an image before doing copy, crop, resize, and thumbnail processing. This results in double the memory as the image data has to be filled in a new image resource. Specifically this is done below.

IN: libraries/CBLib/Imagine/Gd/Image.php
ON: Line 600 (function createImage)

Creating even an empty GD resource of large size results in large memory usage.

https://www.joomlapolis.com/forum/255-developer-members-support/233472-where-to-increase-memory-which-is-needed-for-upload