pset4 filter blur problem

Question

the images is blurry but the check gives errors (it only blurs correctly the edges and corners apparently ...):

• :( blur correctly filters middle pixel expected "127 140 149\n", not "120 133 143\n"
• :) blur correctly filters pixel on edge
• :) blur correctly filters pixel in corner
• :( blur correctly filters 3x3 image expected "70 85 95\n80 9...", not "70 85 95\n80 9..."
• :( blur correctly filters 4x4 image expected "70 85 95\n80 9...", not "70 85 95\n80 9..."

not sure what i`m missing...? grateful for any opinions :D

void blur(int height, int width, RGBTRIPLE image[height][width])
{
    int averageRed;
    int averageGreen;
    int averageBlue;
    RGBTRIPLE copy[height][width];
    
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            // blur top row
            if (i == 0)
            {
                // blur top left corner
                if (j == 0)
                {
                    averageRed = round((image[i][j].rgbtRed + image[i][j + 1].rgbtRed + image[i + 1][j].rgbtRed + image[i + 1][j + 1].rgbtRed) / 4.0);
                    averageGreen = round((image[i][j].rgbtGreen + image[i][j + 1].rgbtGreen + image[i + 1][j].rgbtGreen + image[i + 1][j + 1].rgbtGreen) / 4.0);
                    averageBlue = round((image[i][j].rgbtBlue + image[i][j + 1].rgbtBlue + image[i + 1][j].rgbtBlue + image[i + 1][j + 1].rgbtBlue) / 4.0);
                }
                // blur the top right corner
                else if (j == width - 1)
                {
                    averageRed = round((image[i][j].rgbtRed + image[i][j - 1].rgbtRed + image[i + 1][j].rgbtRed + image[i + 1][j - 1].rgbtRed) / 4.0);
                    averageGreen = round((image[i][j].rgbtGreen + image[i][j - 1].rgbtGreen + image[i + 1][j].rgbtGreen + image[i + 1][j - 1].rgbtGreen) / 4.0);
                    averageBlue = round((image[i][j].rgbtBlue + image[i][j - 1].rgbtBlue + image[i + 1][j].rgbtBlue + image[i + 1][j - 1].rgbtBlue) / 4.0);
                }
                // blur the top edge
                else
                {
                    averageRed = round((image[i][j].rgbtRed + image[i][j - 1].rgbtRed + image[i][j + 1].rgbtRed + image[i + 1][j].rgbtRed + image[i + 1][j - 1].rgbtRed + image[i + 1][j + 1].rgbtRed) / 6.0);
                    averageGreen = round((image[i][j].rgbtGreen + image[i][j - 1].rgbtGreen + image[i][j + 1].rgbtGreen + image[i + 1][j].rgbtGreen + image[i + 1][j - 1].rgbtGreen + image[i + 1][j + 1].rgbtGreen) / 6.0);
                    averageBlue = round((image[i][j].rgbtBlue + image[i][j - 1].rgbtBlue + image[i][j + 1].rgbtBlue + image[i + 1][j].rgbtBlue + image[i + 1][j - 1].rgbtBlue + image[i + 1][j + 1].rgbtBlue) / 6.0);
                }
            }
            //blur the bottom row
            else if (i == height - 1)
            {
                // blur bottom left corner
                if (j == 0)
                {
                    averageRed = round((image[i][j].rgbtRed + image[i][j + 1].rgbtRed + image[i - 1][j].rgbtRed + image[i - 1][j + 1].rgbtRed) / 4.0);
                    averageGreen = round((image[i][j].rgbtGreen + image[i][j + 1].rgbtGreen + image[i - 1][j].rgbtGreen + image[i - 1][j + 1].rgbtGreen) / 4.0);
                    averageBlue = round((image[i][j].rgbtBlue + image[i][j + 1].rgbtBlue + image[i - 1][j].rgbtBlue + image[i - 1][j + 1].rgbtBlue) / 4.0);
                }
                // blur the bottom right corner
                else if (j == width - 1)
                {
                    averageRed = round((image[i][j].rgbtRed + image[i][j - 1].rgbtRed + image[i - 1][j].rgbtRed + image[i - 1][j - 1].rgbtRed) / 4.0);
                    averageGreen = round((image[i][j].rgbtGreen + image[i][j - 1].rgbtGreen + image[i - 1][j].rgbtGreen + image[i - 1][j - 1].rgbtGreen) / 4.0);
                    averageBlue = round((image[i][j].rgbtBlue + image[i][j - 1].rgbtBlue + image[i - 1][j].rgbtBlue + image[i - 1][j - 1].rgbtBlue) / 4.0);
                }
                // blur the top edge
                else
                {
                    averageRed = round((image[i][j].rgbtRed + image[i][j - 1].rgbtRed + image[i][j + 1].rgbtRed + image[i - 1][j].rgbtRed + image[i - 1][j - 1].rgbtRed + image[i - 1][j + 1].rgbtRed) / 6.0);
                    averageGreen = round((image[i][j].rgbtGreen + image[i][j - 1].rgbtGreen + image[i][j + 1].rgbtGreen + image[i - 1][j].rgbtGreen + image[i - 1][j - 1].rgbtGreen + image[i - 1][j + 1].rgbtGreen) / 6.0);
                    averageBlue = round((image[i][j].rgbtBlue + image[i][j - 1].rgbtBlue + image[i][j + 1].rgbtBlue + image[i - 1][j].rgbtBlue + image[i - 1][j - 1].rgbtBlue + image[i - 1][j + 1].rgbtBlue) / 6.0);
                }
            }
            
            else
            {
                // blur the left edge
                if (j == 0)
                {
                    averageRed = round((image[i][j].rgbtRed + image[i][j + 1].rgbtRed + image[i + 1][j].rgbtRed + image[i + 1][j + 1].rgbtRed + image[i - 1][j].rgbtRed + image[i - 1][j + 1].rgbtRed) / 6.0);
                    averageGreen = round((image[i][j].rgbtGreen + image[i][j + 1].rgbtGreen + image[i + 1][j].rgbtGreen + image[i + 1][j + 1].rgbtGreen + image[i - 1][j].rgbtGreen) + image[i - 1][j + 1].rgbtGreen/ 6.0);
                    averageBlue = round((image[i][j].rgbtBlue + image[i][j + 1].rgbtBlue + image[i + 1][j].rgbtBlue + image[i + 1][j + 1].rgbtBlue) + image[i - 1][j].rgbtBlue + image[i - 1][j + 1].rgbtBlue/ 6.0);  
                }
                //blur the right edge
                else if (j == width - 1)
                {
                    averageRed = round((image[i][j].rgbtRed + image[i][j - 1].rgbtRed + image[i + 1][j].rgbtRed + image[i + 1][j - 1].rgbtRed + image[i - 1][j].rgbtRed + image[i - 1][j - 1].rgbtRed) / 6.0);
                    averageGreen = round((image[i][j].rgbtGreen + image[i][j - 1].rgbtGreen + image[i + 1][j].rgbtGreen + image[i + 1][j - 1].rgbtGreen + image[i - 1][j].rgbtGreen) + image[i - 1][j - 1].rgbtGreen/ 6.0);
                    averageBlue = round((image[i][j].rgbtBlue + image[i][j - 1].rgbtBlue + image[i + 1][j].rgbtBlue + image[i + 1][j - 1].rgbtBlue) + image[i - 1][j].rgbtBlue + image[i - 1][j - 1].rgbtBlue/ 6.0);
                }
                //blur the middle
                else
                {
                    averageRed = round((image[i][j].rgbtRed + image[i][j - 1].rgbtRed + image[i][j + 1].rgbtRed + image[i + 1][j].rgbtRed + image[i + 1][j - 1].rgbtRed + image[i + 1][j + 1].rgbtRed + image[i - 1][j].rgbtRed + image[i - 1][j - 1].rgbtRed + image[i - 1][j - 1].rgbtRed) / 9.0);
                    averageGreen = round((image[i][j].rgbtGreen + image[i][j - 1].rgbtGreen + image[i][j + 1].rgbtGreen + image[i + 1][j].rgbtGreen + image[i + 1][j - 1].rgbtGreen + image[i + 1][j + 1].rgbtGreen + image[i - 1][j].rgbtGreen + image[i - 1][j - 1].rgbtGreen + image[i - 1][j - 1].rgbtGreen) / 9.0);
                    averageBlue = round((image[i][j].rgbtBlue + image[i][j - 1].rgbtBlue + image[i][j + 1].rgbtBlue + image[i + 1][j].rgbtBlue + image[i + 1][j - 1].rgbtBlue + image[i + 1][j + 1].rgbtBlue + image[i - 1][j].rgbtBlue + image[i - 1][j - 1].rgbtBlue + image[i - 1][j - 1].rgbtBlue) / 9.0);
                }
            }
            //store the new pixel values in the copy image
            copy[i][j].rgbtRed = averageRed;
            copy[i][j].rgbtGreen = averageGreen;
            copy[i][j].rgbtBlue = averageBlue;
        }
    }
    
    //change the image pixels to the values form the copy image
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            image[i][j].rgbtRed = copy[i][j].rgbtRed; 
            image[i][j].rgbtGreen = copy[i][j].rgbtGreen;
            image[i][j].rgbtBlue = copy[i][j].rgbtBlue;
        }
    }
    return;
}

Answer 1

You're adding one pixel twice, and missing one pixel.

The code, as you've written it, is really prone to tiny bugs like that, and they're hard to find. Once you've got it working, consider how you can make it more readable, and less prone to having issues where you copy/paste and forget to change one little thing. You're handling 9 types of pixels separately, and for each one you're writing out exactly which pixels to calculate from. Could you loop over the pixels you're calculating with, and do checking to make sure you're inside the bounds of the image instead?