模糊图像滤镜-C

Question

I've posted this program several other times, but am different troubles with it. I want to write an algorithm to blur an image, and so far have gotten every pixel value of a grayscale image into a **char array. From there, my plan is to go through each pixel, look to its immediate neighboring pixels, sum the values of them AND the pixel I am currently looking at, and get the average of all of those pixels.

After that is done, I want to set the pixel I'm currently looking at to that average value. I've written partial code for this, and I believe I'm adding it up correctly, but still do not get a resulting image. Must I provide a cast to my sum before assigning it back to the pixel?

Code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    FILE *fin, *fout;
    char path_in[64], path_out[64];
    unsigned char **rev, px;
    int sum, width, height, read, row, i, j;

    printf("Input file name: ");
    scanf("%s", path_in);
    printf("Output file name: ");
    scanf("%s", path_out);

    printf("Width of image (in pixels): ");
    scanf("%d", &width);
    printf("Height of image (in pixels): ");
    scanf("%d", &height);

    fin = fopen(path_in, "rb");
    fout = fopen(path_out, "wb");

    rev = (unsigned char **)malloc(height * sizeof(unsigned char *));
    for(i = 0; i < height; i++)
        rev[i] = (unsigned char *)malloc(width * sizeof(unsigned char));

    for(i = 0; i < height; i++)
    {
        for(j = 0; j < width; j++)
        {
            read = fread(&px, sizeof(char), 1, fin);
            rev[i][j] = px;
        }
    }

    sum = 0;
    for(i = 0; i < height; i++)
    {
        for(j = 0; j < width; j++)
        {
            //Top row of image
            if(i == 0)
            {
                if(j == 0)
                    sum = ((unsigned)rev[i][j] + (unsigned)rev[i][j + 1] + 
                            (unsigned)rev[i + 1][j] + (unsigned)rev[i + 1][j + 1]) / 4;
                else if(j == width - 1)
                    sum = ((unsigned)rev[i][j] + (unsigned)rev[i][j - 1] +
                            (unsigned)rev[i + 1][j] + (unsigned)rev[i + 1][j - 1]) / 4;
                else
                    sum = ((unsigned)rev[i][j] + (unsigned)rev[i][j - 1] + (unsigned)rev[i][j + 1] +
                            (unsigned)rev [i + 1][j] + (unsigned)rev[i + 1][j - 1] + (unsigned)rev[i + 1][j + 1]) / 6;
            }
            //Bottom row of image
            else if(i == height - 1)
            {
                if(j == 0)
                    sum = ((unsigned)rev[i][j] + (unsigned)rev[i][j + 1] + 
                            (unsigned)rev[i - 1][j] + (unsigned)rev[i - 1][j + 1]) / 4;
                else if(j == width - 1)
                    sum = ((unsigned)rev[i][j] + (unsigned)rev[i][j - 1] +
                            (unsigned)rev[i - 1][j] + (unsigned)rev[i - 1][j - 1]) / 4;
                else
                    sum = ((unsigned)rev[i][j] + (unsigned)rev[i][j - 1] + (unsigned)rev[i][j + 1] +
                            (unsigned)rev[i - 1][j] + (unsigned)rev[i - 1][j - 1] + (unsigned)rev[i - 1][j + 1]) / 6;
            }
            //Left side of image (excluding top or bottom row)
            else if(j == 0)
                sum = ((unsigned)rev[i][j] + (unsigned)rev[i - 1][j] + (unsigned)rev[i + 1][j] +
                        (unsigned)rev[i][j + 1] + (unsigned)rev[i - 1][j + 1] + (unsigned)rev[i + 1][j + 1]) / 6;
            //Right side of image (excluding top or bottom row)
            else if(j == width - 1)
                sum = ((unsigned)rev[i][j] + (unsigned)rev[i - 1][j] + (unsigned)rev[i + 1][j] + 
                        (unsigned)rev[i][j - 1] + (unsigned)rev[i - 1][j - 1] + (unsigned)rev[i + 1][j - 1]) / 6;
            rev[i][j] = (unsigned char)sum;         
        }
    }

    for(i = 0; i < height; i++)
    {
        for(j = 0; j < width; j++)
        {
            if(j < width && i < height)
                fwrite(&rev[i][j], sizeof(char), 1, fout);
        }
    }

    fclose(fout);
    fclose(fin);

    return 0;
}

Note : this code only works with .raw grayscale images.

EDIT : I've implemented blurring to the rest of the image, but am still not getting a readable output file. I'm not sure if my arithmetic is correct, as I'm not too familiar with adding bytes together.

Answer 1

This part

rev = (char **)malloc(height * sizeof(char *));
for(i = 0; i < width; i++)
    rev[i] = (char *)malloc(width * sizeof(char));

I think you meant

for(i = 0; i < height; i++)

Other bugs:

• you probably want to use unsigned char as the data type
• don't use sum += , use sum =
• you're only doing the blur calculation for the first row of the image
• you might want to convert each input used in the calculation to unsigned , otherwise the values will overflow

try:

for(i = 0; i < (height - 1); i++)
{
    for(j = 0; j < (width - 1); j++)
    {
        sum = ((unsigned) rev[i][j] + (unsigned) rev[i][j + 1] + 
          (unsigned) rev[i + 1][j] + (unsigned) rev[i + 1][j + 1]) / 4;
        rev[i][j] = (unsigned char) sum;
    }
}