result black or white filter edges

Question

    int superior( float value);
// Detect edges
void edges(int height, int width, RGBTRIPLE image[height][width])
{
    float red_x, green_x, blue_x, red_y ,green_y ,blue_y ;
    red_x = green_x = blue_x = red_y = green_y = blue_y = 0.0;

//create a copy of original imgcopy to save original pixel values
RGBTRIPLE imgcopy[height][width];
    for (int row = 0; row < height; row++)
    {
        for (int w = 0; w < width; w++)
        {
            imgcopy[row][w].rgbtRed = image[row][w].rgbtRed;
            imgcopy[row][w].rgbtGreen = image[row][w].rgbtGreen;
            imgcopy[row][w].rgbtBlue = image[row][w].rgbtBlue;
        }
    }
    //
    for (int row = 0; row < height; row++)
    {
        for (int col = 0; col < width; col++)
        {
            //up
            if (row > 0)
            {
                red_y += -2 * imgcopy[row - 1][col].rgbtRed;
                green_y += -2 * imgcopy[row - 1][col].rgbtGreen;
                blue_y += -2 * imgcopy[row - 1][col].rgbtBlue;
            }
            //down
             if ( row < height -1)
            {
                red_y += 2 * imgcopy[row + 1][col].rgbtRed ;
                green_y += 2 * imgcopy[row + 1][col].rgbtGreen;
                blue_y += 2 * imgcopy[row + 1][col].rgbtBlue;
            }
            //left
             if(col > 0)
            {
                red_x += - 2 * imgcopy[row][col -1].rgbtRed ;
                green_x += - 2 * imgcopy[row][col -1].rgbtGreen;
                blue_x += - 2 * imgcopy[row][col -1].rgbtBlue;
            }
            //right 
             if ( col < width -1)
            {
                red_x += 2 * imgcopy[row][col + 1].rgbtRed;
                green_x += 2 * imgcopy[row][col + 1].rgbtGreen;
                blue_x += 2 * imgcopy[row][col + 1].rgbtBlue;
            }
            //top left
             if ( row > 0 && col > 0) 
            {
                red_x += -1 * imgcopy[row -1][col - 1].rgbtRed;
                green_x += -1 * imgcopy[row -1][col - 1].rgbtGreen;
                blue_x += -1 * imgcopy[row -1][col - 1].rgbtBlue;
                red_y += -1 * imgcopy[row - 1][col - 1].rgbtRed ;
                green_y += -1 * imgcopy[row - 1][col -1].rgbtGreen;
                blue_y += -1 * imgcopy[row - 1][col -1].rgbtBlue;
            }
            //top right
             if ( row > 0 && col < width -1)
            {
                red_x += 1 * imgcopy[row -1][col + 1].rgbtRed;
                green_x += 1 * imgcopy[row -1][col + 1].rgbtGreen;
                blue_x += 1 * imgcopy[row -1][col + 1].rgbtBlue;
                red_y += -1 * imgcopy[row - 1][col + 1].rgbtRed ;
                green_y += -1 * imgcopy[row - 1][col + 1].rgbtGreen;
                blue_y += -1 * imgcopy[row - 1][col + 1].rgbtBlue;
            }
               //bot right
             if ( row < height -1 && col < width -1)
            {
                red_x += 1 * imgcopy[row +1][col + 1].rgbtRed;
                green_x += 1 * imgcopy[row +1][col + 1].rgbtGreen;
                blue_x += 1 * imgcopy[row +1][col + 1].rgbtBlue;
                red_y += 1 * imgcopy[row + 1][col + 1].rgbtRed ;
                green_y += 1 * imgcopy[row + 1][col + 1].rgbtGreen;
                blue_y += 1 * imgcopy[row + 1][col + 1].rgbtBlue;
            }
            //bot left
             if ( row < height -1 && col > 0)
            {
                red_x += -1 * imgcopy[row +1][col - 1].rgbtRed;
                green_x += -1 * imgcopy[row +1][col - 1].rgbtGreen;
                blue_x += -1 * imgcopy[row +1][col -1].rgbtBlue;
                red_y += 1 * imgcopy[row + 1][col - 1].rgbtRed ;
                green_y += 1 * imgcopy[row + 1][col - 1].rgbtGreen;
                blue_y += 1 * imgcopy[row + 1][col - 1].rgbtBlue;
            }
    
        image[row][col].rgbtRed =  superior(sqrt(( red_x * red_x) + (red_y * red_y)));
        image[row][col].rgbtGreen = superior(sqrt(( green_x * green_x )+ (green_y * green_y)));
        image[row][col].rgbtBlue =  superior( sqrt(( blue_x * blue_x) + (blue_y * blue_y)));
    }
}
return;
}
// //                     //./filter -e images/yard.bmp out.bmp

int superior(float value)
{
    int result =0;
    if (value > 255) 

    {
        result = 255;
    }
    else if( value < 0)
    {
        result =0;
    }
    else 
    {
        result = round(value);
    }
return result;
}

Answer 1

It looks your main issue is not resetting the red_x, green_x, etc values to 0 between iterations.