CS50 PSET4边缘函数不正确过滤边缘和角红像素值

Question

我试图用Sobel算子在图像中编写一个边缘检测函数。这是CS50课程中问题集4-过滤器(更多)的一部分.链接这里 (仅边缘部分)。

所编写的函数是正确地过滤图像的中间像素，但没有为边缘和边框像素提供所需的输出，而对于红色像素值(只有)来说，这一点太令人惊讶了，其余的都是正确的。

我已经手动检查了代码，调试了几次，但仍然找不到bug。任何帮助都将不胜感激。

谢谢。

这是边缘函数的代码。

// Detect edges
void edges(int height, int width, RGBTRIPLE image[height][width])
{

    // Array for storing corresponding gx values of the pixels.
    RGBTRIPLE(*gx)[width] = calloc(height, width * sizeof(RGBTRIPLE));
    if (gx == NULL)
    {
        printf("Not enough memory to store blur pixels.\n");
        return;
    }

    // Array for storing corresponding gy values of the pixels.
    RGBTRIPLE(*gy)[width] = calloc(height, width * sizeof(RGBTRIPLE));
    if (gy == NULL)
    {
        printf("Not enough memory to store blur pixels.\n");
        return;
    }


    for (int row = 0; row < height; row++)
    {
        for (int col = 0; col < width; col++)
        {
            Gx(row, col, height, width, image, gx);
            Gy(row, col, height, width, image, gy);
        }
    }

    for (int row = 0; row < height; row++)
    {
        for (int col = 0; col < width; col++)
        {
            image[row][col].rgbtBlue = r_sqrt_sum(gx[row][col].rgbtBlue, gy[row][col].rgbtBlue);
            image[row][col].rgbtGreen = r_sqrt_sum(gx[row][col].rgbtGreen, gy[row][col].rgbtGreen);
            image[row][col].rgbtRed = r_sqrt_sum(gx[row][col].rgbtRed, gy[row][col].rgbtRed);

        }
    }

    free(gx);
    free(gy);
    return;
}

Gx和Gy功能代码。

void Gx(int row, int col, int height, int width, RGBTRIPLE matrix[height][width], RGBTRIPLE new_matrix[height][width])
// This function will return Gx value of a given pixel.
{
    float Blue = 0;
    float Green = 0;
    float Red = 0;

    for (int i = -1; i < 2; i++)
    {
        for (int j = -1; j < 2; j++)
        {
            // for rows and columns out of range.
            if ((i + row) < 0 || (i + row >= height) || (j + col) < 0 || (j + col >= width))
            {
                continue;
            }

            // for (-1,-1) and (1,-1)
            else if ((i == -1 && j == -1) || (i == 1 && j == -1))
            {
                Blue += matrix[i + row][j + col].rgbtBlue * -1;
                Green += matrix[i + row][j + col].rgbtGreen * -1;
                Red += matrix[i + row][j + col].rgbtRed * -1;
            }

            // for (0,-1)
            else if ((i == 0 && j == -1))
            {
                Blue += matrix[i + row][j + col].rgbtBlue * -2;
                Green += matrix[i + row][j + col].rgbtGreen * -2;
                Red += matrix[i + row][j + col].rgbtRed * -2;
            }

            // for (-1, 0) , (0, 0), (1, 0)
            else if ((i == -1 && j == 0) || (i == 0 && j == 0) || (i == 1 && j == 0))
            {
                Blue += matrix[i + row][j + col].rgbtBlue * 0;
                Green += matrix[i + row][j + col].rgbtGreen * 0;
                Red += matrix[i + row][j + col].rgbtRed * 0;
            }

            // for (0, 1)
            else if ((i == 0 && j == 1))
            {
                Blue += matrix[i + row][j + col].rgbtBlue * 2;
                Green += matrix[i + row][j + col].rgbtGreen * 2;
                Red += matrix[i + row][j + col].rgbtRed * 2;
            }

            // for (-1,1) and (1,1)
            else if ((i == -1 && j == 1) || (i == 1 && j == 1))
            {
                Blue += matrix[i + row][j + col].rgbtBlue * 1;
                Green += matrix[i + row][j + col].rgbtGreen * 1;
                Red += matrix[i + row][j + col].rgbtRed * 1;
            }
        }
    }

    new_matrix[row][col].rgbtBlue = fabsf(Blue);
    new_matrix[row][col].rgbtGreen = fabsf(Green);
    new_matrix[row][col].rgbtRed = fabsf(Red);
}


void Gy(int row, int col, int height, int width, RGBTRIPLE matrix[height][width], RGBTRIPLE new_matrix[height][width])
// This function will return Gy value of a given pixel.
{
    float Blue = 0;
    float Green = 0;
    float Red = 0;

    for (int i = -1; i < 2; i++)
    {
        for (int j = -1; j < 2; j++)
        {
            // for rows and columns out of range.
            if ((i + row) < 0 || (i + row >= height) || (j + col) < 0 || (j + col >= width))
            {
                continue;
            }

            // for (-1,-1) and (-1,1)
            else if ((i == -1 && j == -1) || (i == -1 && j == 1))
            {
                Blue += matrix[i + row][j + col].rgbtBlue * -1;
                Green += matrix[i + row][j + col].rgbtGreen * -1;
                Red += matrix[i + row][j + col].rgbtRed * -1;
            }

            // for (-1, 0)
            else if ((i == -1 && j == 0))
            {
                Blue += matrix[i + row][j + col].rgbtBlue * -2;
                Green += matrix[i + row][j + col].rgbtGreen * -2;
                Red += matrix[i + row][j + col].rgbtRed * -2;
            }

            // for (0, -1) , (0, 0), (0, 1)
            else if ((i == 0 && j == -1) || (i == 0 && j == 0) || (i == 0 && j == 1))
            {
                // printf("for (%d, %d) considering (%d, %d) and using -1 \n", row, col, row+i, col+j);
                Blue += matrix[i + row][j + col].rgbtBlue * 0;
                Green += matrix[i + row][j + col].rgbtGreen * 0;
                Red += matrix[i + row][j + col].rgbtRed * 0;
            }

            // for (1, 0)
            else if ((i == 1 && j == 0))
            {
                Blue += matrix[i + row][j + col].rgbtBlue * 2;
                Green += matrix[i + row][j + col].rgbtGreen * 2;
                Red += matrix[i + row][j + col].rgbtRed * 2;
            }

            // for (1,-1) and (1,1)
            else if ((i == 1 && j == -1) || (i == 1 && j == 1))
            {
                Blue += matrix[i + row][j + col].rgbtBlue * 1;
                Green += matrix[i + row][j + col].rgbtGreen * 1;
                Red += matrix[i + row][j + col].rgbtRed * 1;
            }
        }
    }

    new_matrix[row][col].rgbtBlue = fabsf(Blue);
    new_matrix[row][col].rgbtGreen = fabsf(Green);
    new_matrix[row][col].rgbtRed = fabsf(Red);
}

r_sqrt_sum函数的代码。

int r_sqrt_sum(float a, float b)
// Return rounded sqrt of sum of squared a and b.
{
    float x = round(sqrt((a*a + b*b)));

    if (x > 255) return 255;

    else return x;
}

Answer 1

所以我被困了这么久的问题终于解决了。在上述代码中(在Gx和Gy函数中)，我在RGBTRIPLE类型的new_matrix中附加了绿色、蓝色、红色的值。当浮子的值可能大于8位时，它只能占用8位。对于这个问题，我定义了一个新的结构：

typedef struct
{
    float  rgbtBlu;
    float  rgbtGree;
    float  rgbtRe;
} __attribute__((__packed__))
RGBFTRIPLE;

并将new_matrix()类型从RGBTRIPLE更改为RGBFTRIPLE，从而使获取更大的值成为可能。这解决了问题。

感谢整个社会对这几个问题的回答，并消除了我的疑虑。