iOS Take screenshot with GPUImageview Programatically

I am working on GPUImageView Based application. I have implemented all functionality correctly but i am not able to capture Screenshot with GPUImageview.

Here is my Scenario ..

Here i have also Attached Demo on My Github. Please help me regarding this issue.

GPUImageview Demo

Note :- I have tried to take a screenshot with renderInContext: but it not helpfull for me . Thank you.