Seeking Guidance on Implementing Sobel Edge Detection for BMP Images on DE0 Experiment Board with SD

Hi,

I first conducted practical tests on SD card read/write functionality using official Altera documentation(.pdf). Following that, I incorporated the Sobel filter and proceeded to modify the code.

I may have errors in the code I provided earlier, and I will make corrections.

This time, I will attach the results of the Sobel operation. I used Python to convert the text file to PNG for observation. Since I haven't been able to successfully write back to the SD card yet, I manually copied the results from the Nios II Console.

Original:

I have included the code for writing back to the SD card.

result image:

no writing back to the SD card.

result image:

It's intriguing that after adding the code to write back to the SD card, the Sobel results differ. Removing that part seems to restore the original Sobel outcomes. Currently, I am unable to resolve the issue of not being able to write all Sobel results to the SD card at once, managing to successfully write back only 769 sets of data.

The Sobel results seem to be relatively consistent, with no apparent differences.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <altera_up_sd_card_avalon_interface.h>

#define WIDTH 100
#define HEIGHT 100

// 3x3 Sobel operators for gradient calculation
int sobel_x[3][3] = {{-1, 0, 1}, {-2, 0, 2}, {-1, 0, 1}};
int sobel_y[3][3] = {{-1, -2, -1}, {0, 0, 0}, {1, 2, 1}};

void applySobel(short int* imageData, unsigned char* resultData) {
    memset(resultData, 0, WIDTH * HEIGHT);

    for (int y = 1; y < HEIGHT - 1; y++) {
        for (int x = 1; x < WIDTH - 1; x++) {
            int gx = 0, gy = 0;

            // Convolution with Sobel operators
            for (int i = -1; i <= 1; i++) {
                for (int j = -1; j <= 1; j++) {
                    int pixelValue = imageData[(y + i) * WIDTH + (x + j)];
                    gx += sobel_x[i + 1][j + 1] * pixelValue;
                    gy += sobel_y[i + 1][j + 1] * pixelValue;
                }
            }

            // Calculate gradient magnitude
            int magnitude = (int)sqrt((double)(gx * gx + gy * gy));

            // Clamp magnitude to 0-255
            magnitude = (magnitude > 255) ? 255 : ((magnitude < 0) ? 0 : magnitude);

            resultData[y * WIDTH + x] = (unsigned char)magnitude;
        }
    }
}

int main() {
    short int sd_fileh,sd_fileh2;
    alt_up_sd_card_dev *sd_card_dev = alt_up_sd_card_open_dev(ALTERA_UP_SD_CARD_AVALON_INTERFACE_0_NAME);

    if (sd_card_dev != 0 && alt_up_sd_card_is_Present() && alt_up_sd_card_is_FAT16()) {
        sd_fileh = alt_up_sd_card_fopen("test8.txt", false);

        if (sd_fileh >= 0) {
            short int imageData[WIDTH * HEIGHT];
            unsigned char resultData[WIDTH * HEIGHT];

            printf("Reading data from test8.txt:\n");

            // Read image data into the array
            for (int i = 0; i < WIDTH * HEIGHT; i++) {
                char buffer[10];
                int j;
                for (j = 0; j < 4; j++) {  // 根據你的像素值調整大小
                	char currentChar = alt_up_sd_card_read(sd_fileh);
                    if (currentChar == -1 || currentChar == '\n') {
                    	break; // 到達檔案結尾或換行字元
                    }
                    buffer[j] = currentChar;
                }
                if (j == 0) {
                    break;
                }
                buffer[j] = '\0';
                printf("%s\n", buffer);
                imageData[i] = atoi(buffer);
            }

            // Apply Sobel operator to the image data
            applySobel(imageData, resultData);

            // Print the Sobel operation result
            printf("Sobel operation result:\n");
            for (int i = 0; i < WIDTH * HEIGHT; i++) {
                printf("%d\n", resultData[i]);

            }
            // Close the original file
            alt_up_sd_card_fclose(sd_fileh);

//            // Create and write the result to test11.txt
//            sd_fileh2 = alt_up_sd_card_fopen("test11.txt", true);
//            if (sd_fileh2 >= 0) {
//                for (int i = 0; i < WIDTH * HEIGHT; i++) {
//                    char buffer[10];
//                    sprintf(buffer, "%d\n", resultData[i]);
//                    alt_up_sd_card_write(sd_fileh2, buffer);
//                }
//                alt_up_sd_card_fclose(sd_fileh2);
//                printf("Sobel result written to test11.txt\n");
//            } else {
//                printf("Problem opening or writing to file. Error %i\n", sd_fileh);
//            }
//
//            // Close the original file
//            alt_up_sd_card_fclose(sd_fileh2);

        } else {
            printf("Problem opening file. Error %i\n", sd_fileh);
        }
    } else {
        printf("SD card not available or not in FAT16 format\n");
    }

    return 0;
}