It was my design choice, for reasons of wrapping my head around the logic, to launch 3 two-dimensional grids per image, one per colour channel, instead of preparing a 3 dimensional grid and somehow utilizing the z member. We pass the current iteration (z) to use in calculating the correct location for single dimensional representation of the image:  <nowiki>// Launch grid 3 times (one grid per colour channel)std::cout << "Performing rotation ..." << std::endl;for (int i = 0; i < 3; i++) { rot90 << <dGrid, dBlock >> > (d_src, d_dst, w, h, i);}</nowiki>