You would benefit from starting a new thread with a catchy title, to attract users who are familiar with your issue. This thread is really about Photoshop, and you are not running Photoshop.
Be sure to lay out your symptoms in detail not just camp-on someone elses description. Readers will be eager to help you with your specific probelm.
Seraching and searching everywhere, I've probably found the explanation for this problem:
The Intel HD 4000 graphic card consumes up to 768Mb from RAM. That's why kernel_task is using this amount of memory.
Hope this helps.