Hardware accelerated effect on texture


I am here to get some advices.
My projet uses OpenCV to open video streams and use SDL2 to create a mosaic with these streams.
I use SDL_texture to have hardware acceleration.

I would like to apply HW accelerated effect (ie grayscale, posterize, etc) via opengl.
As far as I read, I have to go full opengl? am I rigtht? is there a non full opengl hardware accelerated solution?

I am pretty new at opengl and SDL2, Thank advance for your answers