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Team KCM

Team Members

  1. Byungho Kim, Some responsibility
  2. Taeyang Chung, Some responsibility
  3. SeungYeon Moon, Some responsibility

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Assignment 1

Byungho's Findings


To enhance image quality, most of S/W use convolution algorithm with sharpen kernel. The convolution algorithm is based on pixel window and kernel multiplication and the kernel which consists of 3 x 3 matrix or 5 x 5 matrix. Therefore, as we learned at the GPU610 class, I can speed up the program using CUDA library

Original Image Enhanced Image

These two images show the result of the S/W. Left picture is the original image and right picture is obtained by the S/W. 3x3 matrix sharpen kernel is used.

6 x 4 Pixel Small Image
IP11 IP12 IP13 IP14 IP15 IP16
IP21 IP22 IP23 IP24 IP25 IP26
IP31 IP32 IP33 IP34 IP35 IP36
IP41 IP42 IP43 IP44 IP45 IP46

K0 K1 K2
K3 K4 k5
k6 k7 k8

The 33th output pixel will be given by

OP33 = IP22 x K0 + IP23 x K1 + IP24 x K2 + IP32 x K3 + IP33 x K4 + IP34 x K5 + IP42 x K6 + IP43 x K7 + IP44 x K8


The profile shows that filter function occupies the most of processing time.

  %   cumulative   self              self     total          
 time   seconds   seconds    calls  ns/call  ns/call  name   
 93.59      1.46     1.46                             filter(image_t*, double*, int, double, double)
  6.41      1.56     0.10  5038848    19.85    19.85  put_pixel_unsafe(image_t*, unsigned int, unsigned int, unsigned char, unsigned char, unsigned char)
  0.00      1.56     0.00        2     0.00     0.00  alloc_img(unsigned int, unsigned int)
  0.00      1.56     0.00        1     0.00     0.00  _GLOBAL__sub_I__Z7get_ppmP8_IO_FILE
  0.00      1.56     0.00        1     0.00     0.00  get_ppm(_IO_FILE*)

In the filter function, 3 x 3 mask walk through all RGB pixels and calculate convolution of them.

image filter(image im, double *K, int Ks, double divisor, double offset)
    image oi;
    unsigned int ix, iy, l;
    int kx, ky;
    double cp[3];
    oi = alloc_img(im->width, im->height);
    if ( oi != NULL ) {
        for(ix=0; ix < im->width; ix++) {
            for(iy=0; iy < im->height; iy++) {
                cp[0] = cp[1] = cp[2] = 0.0;
                for(kx=-Ks; kx <= Ks; kx++) {
                    for(ky=-Ks; ky <= Ks; ky++) {
                        for(l=0; l<3; l++)
                            cp[l] += (K[(kx+Ks) +
                                    (ky+Ks)*(2*Ks+1)]/divisor) *
                                ((double)GET_PIXEL_CHECK(im, ix+kx, iy+ky, l)) + offset;
                for(l=0; l<3; l++)
                    cp[l] = (cp[l]>255.0) ? 255.0 : ((cp[l]<0.0) ? 0.0 : cp[l]) ;
                put_pixel_unsafe(oi, ix, iy,
        return oi;
   return NULL;

Taeyang's Findings

My program is to solve the heat transfer problem using explicit method. I found this source code at

The 'Solve()' function takes 3 arguments and as t-value decreases the processing time increases as shown below A1 3.png

A1 4.png

The 'Solve()' function:

      void solve(){
               int j=0;
                       for(int k=1;k<xGridNum;k++){
                            solutionNew[k] = solutionLast[k]+dt*(K/dx/dx*

By Implementing parallel solution, I believe I can shorten the processing time.

SeungYeon's Findings

There are many types of image processing or operations can be done. Some of examples are rotating,re-sizing,blurring, etc... For Assignment 1, I decided to work with one of the operation that can be done with an image in c++, which deals with brightness and contrast of an image. I was able to find a open source code from "openCV" website it stands for Open Source Computer Vision, is open source libraries developed by Intel for image and video processing. The libraries can be installed in any platform, and i was able to install it in my windows platform, and all test runs all done using visual studio 2013, Test file is compiled and profiled using performance wizard vs13. Following website is an official documentation website of openCV libraries, with code examples for many image and video type operations

The open source code for the program requires 3 user inputs which are path to an image and alpha,beta values which will be multiplied and added to each pixels' in the image. To make sure test run is accurate, i had to change some code in the program and hard code in the values for alpha and beta.

Here is two test runs using same image but in different file size

Test run with an image size of 500KB

Test run 500KB total.png

Total Time takes is 12 seconds

Test run 500KB.png

Test run with an image size of 2MB

Test run 2MB total.png

Total Time takes is 14 seconds

Test run 2MB.png

SeungYeons' observation for As_1

Changing contrast and brightness of an image in the function is implemented with a scale * matrix operation. M_A(x,y) = ALPHA * M_B(x,y) + BETA;

Assignment 2

For our Assignment 2 we decided to work with heat transfer problem.

To compare the speed difference between the original code and parallelized code, we first profiled the original code in matrix environment an parallelized code in school computer. (using gporf and nvvp)

Profile results

Each Program was tested with 5 different input data.(500,1000,2500,5000,10000)

Profile #1 (Original code)

Sample Data = 500


Sample Data = 2500


Sample Data = 10000


Profile #2 (GPU implementation version)

Sample Data = 500


Sample Data = 2500


Sample Data = 10000


Summary of profiling

We tested CPU and GPU implementation version with same data sizes and showed significant speedup in result after using kernel.

Summary of profiling in Chart


Charts with some of main operation(function) calls for CPU version and GPU(kernel)



GPU (kernel)


Screen shot of solve function in CPU and GPU(kernel) versions



GPU(Solve) and Kernel



Assignment 3

For assignment 3, we were checking everything we can do to improve the performance and found 2 thing we can do. Firstly, in the while loop, there were 6 times of memory copy functions called, and we found that we can reduce 6 times to 1 time by using device address pointer switching. Furthermore, we found that if the sample number n is less that 1024, we can use shared memory in the kernel.

Reduce Memory Copy Function Calls

Assignment 2 Source Code

                                cudaMemcpy(d_x, x, (xGridNum + 1) * sizeof(float), cudaMemcpyHostToDevice);
                                cudaMemcpy(d_solutionLast, solutionLast, xGridNum * sizeof(double), cudaMemcpyHostToDevice);
                                cudaMemcpy(d_solutionNew, solutionNew, xGridNum * sizeof(double), cudaMemcpyHostToDevice);


                                kernel<<<(xGridNum + ntpb - 1) / ntpb, ntpb>>>(d_solutionNew, d_solutionLast, d_x, xGridNum, dt, dx, K, j);

                                cudaMemcpy(x, d_x, (xGridNum + 1) * sizeof(float), cudaMemcpyDeviceToHost);
                                cudaMemcpy(solutionLast, d_solutionLast, xGridNum * sizeof(double), cudaMemcpyDeviceToHost);
                                cudaMemcpy(solutionNew, d_solutionNew, xGridNum * sizeof(double), cudaMemcpyDeviceToHost);



Improved Source Code

<syntaxhighlight lang="cpp"> void solve(){

   int j=0;
   int d;
   cudaDeviceProp prop;
   cudaGetDeviceProperties(&prop, d);
   unsigned ntpb = prop.maxThreadsDim[0];
   unsigned ntpg = ntpb * prop.maxGridSize[0];
   if (xGridNum > ntpg) {
       xGridNum = ntpg;
       std::cout << "n reduced to " << xGridNum << std::endl;
   double* d_x;
   double* d_solutionA;
   double* d_solutionB;
   cudaMalloc((void**)&d_x, (xGridNum + 1) * sizeof(float));       
   cudaMalloc((void**)&d_solutionA, xGridNum * sizeof(double));
   cudaMalloc((void**)&d_solutionB, xGridNum * sizeof(double));
   double* d_solutionTemp;
   cudaMemcpy(d_x, x, (xGridNum + 1) * sizeof(float), cudaMemcpyHostToDevice);
   cudaMemcpy(d_solutionA, solutionNew, xGridNum * sizeof(double), cudaMemcpyHostToDevice);
   cudaMemcpy(d_solutionB, solutionLast, xGridNum * sizeof(double), cudaMemcpyHostToDevice);
   std::ofstream myfile; ("output.txt");                   
   // A = new, B = last
   while( j < tTotal / dt){                    
       kernel<<<(xGridNum + ntpb - 1) / ntpb, ntpb>>>(d_solutionA, d_solutionB, d_x, xGridNum, dt, dx, K, j);
       cudaMemcpy(solutionNew, d_solutionA, xGridNum * sizeof(double), cudaMemcpyDeviceToHost); 
       myfile << "Time" << tTotal/dt << std::endl;
       for(int i = 0; i <= xGridNum; i++){                                   
         myfile << solutionNew[i] << ":";
       d_solutionTemp = d_solutionA;
       d_solutionA = d_solutionB;
       d_solutionB = d_solutionTemp;

   cudaDeviceReset(); // Important

} <syntaxhighlight>