cs50 filter "blur" pset4 - c

Question

This code for cs50 filter "blur" compiles, but when I run it, it says, index 600 out of bounds for type 'RGBTRIPLE [width].'. I somewhat understand what it means, but I dont know why its saying that I exceeded the array limit.
void blur(int height, int width, RGBTRIPLE image[height][width])
{
int counter = 0;
int sumGreen = 0;
int sumRed = 0;
int sumBlue = 0;
for (int i = 0; i < height; i++)
{
for (int j = 0; j < width; j++)
{
for (int k = i - 1; k <= i + 1; k++)
{
for (int m = j - 1; m <= j + 1; m++)
{
if (k >= 0 && m >= 0 && k <= height && m <= width)
{
sumGreen += image[k][m].rgbtGreen;
sumBlue += image[k][m].rgbtBlue;
sumRed += image[k][m].rgbtRed;
counter++;
}
}
}
image[i][j].rgbtGreen = sumGreen / counter;
image[i][j].rgbtBlue = sumBlue / counter;
image[i][j].rgbtRed = sumRed / counter;
counter = 0;
sumGreen = 0;
sumBlue = 0;
sumRed = 0;
}
}
return;
}

Answer 1

In C, even in CS50, arrays of size N have highest legal index N-1 and start at 0.
With your loops
i gets up to height-1, correct
j gets up to width-1, correct
k starts at -1, incorrect but the if protects
m starts at -1, incorrect but the if protects
k gets up to i+1 which is heigth, incorrect and the if does not protect either
m gets up to j+1 which is width, incorrect and the if does not protect either
You get the "index 600 out of bounds for type 'RGBTRIPLE [width]" because you access
image[k][m].rgbtGreen
with m being equal to width, because of the last bullet point.
That is forbidden because of the first sentence in this answer.
What you need is to change your loops to go from 0 to width-1, especially for the inner loops. For that I would change the outer loops, make them go from 1 to width-2. At that point the protective if should become unneeded, it is broken anyway. It should use < instead of <=.
Then you probably need to treat the picture edges specially.
Same for the height-related parts obviously.