Question

I am having a problem of transposing an image:

I call the kernel method:

    // index of the pixel on the image
    int index_in  = index_x + index_y * width;

    int index_out = index_x + index_y*height;   

    // Allocate the shared memory
    __shared__ unsigned int onchip_storage[16][16];

    // Load the inputs to the shared memory
    onchip_storage[threadIdx.y][threadIdx.x] =  in[index_in];            

    // Save the output value to the memory  
    out[index_out] = onchip_storage[threadIdx.x][threadIdx.y];

I got the image rotated but somehow the colors are not as original. Any idea?

Thanks in advance.

Answer 1

Assuming your RGB components are interleaved, then your algorithm is not handling the three components correctly. You really need to make your tile size a multiple of 3 in width, e.g. 18 x 18. Then when you do the transpose you need to transpose elements which are 3 x 4 = 12 bytes wide.