intergral image with cuda

Blelloch:

For an input array with size n, the scan algorithm has computational complexity of O(n), and it consists of two phases: the reduce phase (or the up-sweep phase) and the down-sweep phase. We can visualize the reduce phase as building a binary tree (Figure
1), at each level reducing the number of nodes by half, and making one addition per node.

Since the operations are performed in place using shared memory, the tree we build is not an actual data structure, but helps explaining the algorithm.





In the down-sweep phase, we traverse the tree from the root to the leaves, and use the partial sums we computed in the reduce phase to obtain the scanned array. We note that the last element is set to zero in the beginning and it propagates to reach
the beginning of the array, thus resulting in an exclusive computation.





CUDA calculate:



CUDPPHandle cudpp_lib;

CUDPP_SAFE_CALL( cudppCreate(&cudpp_lib) );

// Setup cudpp multiscan plans for computing the integral image

CUDPPHandle mscan_plan, mscan_tr_plan;

CUDPPConfiguration cudpp_conf;

cudpp_conf.op = CUDPP_ADD;

cudpp_conf.datatype = CUDPP_FLOAT;

cudpp_conf.algorithm = CUDPP_SCAN;

cudpp_conf.options = CUDPP_OPTION_FORWARD | CUDPP_OPTION_INCLUSIVE;

CUDPP_SAFE_CALL( cudppPlan(cudpp_lib, &mscan_plan, cudpp_conf,

img_width, img_height, gray_img_pitch / sizeof(float)) );

CUDPP_SAFE_CALL( cudppPlan(cudpp_lib, &mscan_tr_plan, cudpp_conf,

img_height, img_width, int_img_tr_pitch / sizeof(float)) );

CUDPP_SAFE_CALL( cudppMultiScan(mscan_plan, d_int_img, d_gray_img, img_width, img_height) );

transposeGPU(d_int_img_tr, int_img_tr_pitch,

d_int_img, int_img_pitch,

img_width, img_height);

CUDPP_SAFE_CALL( cudppMultiScan(mscan_tr_plan, d_int_img_tr2, d_int_img_tr, img_height, img_width) );

transposeGPU(d_int_img, int_img_pitch,

d_int_img_tr2, int_img_tr_pitch,

img_height, img_width);

CUDPP_SAFE_CALL( cudppDestroyPlan(mscan_plan) );

CUDPP_SAFE_CALL( cudppDestroyPlan(mscan_tr_plan) );

CUDPP_SAFE_CALL( cudppDestroy( cudpp_lib ) );

CUDA_SAFE_CALL( cudaFree(d_rgb_img) );

CUDA_SAFE_CALL( cudaFree(d_gray_img) );

CUDA_SAFE_CALL( cudaFree(d_int_img_tr) );

CUDA_SAFE_CALL( cudaFree(d_int_img_tr2) );