CS50 pset4 滤镜模糊 function

Question

我为模糊 function 编写了一个代码，但它返回了错误的 output，原因我不知道（它对我来说看起来不错），这是一个示例（始终相同）：

:( blur correctly filters middle pixel
    expected "127 140 149\n", not "126 140 149\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..."

代码在这里：

void blur(int height, int width, RGBTRIPLE image[height][width])
{
    RGBTRIPLE original[height][width];
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            original[i][j] = image[i][j];
        }
    }
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            if (i == 0)
            {
                if (j == 0)
                {
                    image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i + 1][j].rgbtRed + original[i][j + 1].rgbtRed + original[i + 1][j + 1].rgbtRed) / 4);
                    image[i][j].rgbtGreen = round((original[i][j].rgbtGreen + original[i + 1][j].rgbtGreen + original[i][j + 1].rgbtGreen + original[i + 1][j + 1].rgbtGreen) / 4);
                    image[i][j].rgbtBlue = round((original[i][j].rgbtBlue + original[i + 1][j].rgbtBlue + original[i][j + 1].rgbtBlue + original[i + 1][j + 1].rgbtBlue) / 4);
                }
                else if (j == width - 1)
                {
                    image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i + 1][j].rgbtRed + original[i][j - 1].rgbtRed + original[i + 1][j - 1].rgbtRed) / 4);
                    image[i][j].rgbtGreen = round((original[i][j].rgbtGreen + original[i + 1][j].rgbtGreen + original[i][j - 1].rgbtGreen + original[i + 1][j - 1].rgbtGreen) / 4);
                    image[i][j].rgbtBlue = round((original[i][j].rgbtBlue + original[i + 1][j].rgbtBlue + original[i][j - 1].rgbtBlue + original[i + 1][j - 1].rgbtBlue) / 4);
                }
                else
                {
                    image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i + 1][j].rgbtRed + original[i][j - 1].rgbtRed + original[i + 1][j - 1].rgbtRed + original[i][j + 1].rgbtRed + original[i + 1][j + 1].rgbtRed) / 6);
                    image[i][j].rgbtGreen = round((original[i][j].rgbtGreen + original[i + 1][j].rgbtGreen + original[i][j - 1].rgbtGreen + original[i + 1][j - 1].rgbtGreen + original[i][j + 1].rgbtGreen + original[i + 1][j + 1].rgbtGreen) / 6);
                    image[i][j].rgbtBlue = round((original[i][j].rgbtBlue + original[i + 1][j].rgbtBlue + original[i][j - 1].rgbtBlue + original[i + 1][j - 1].rgbtBlue + original[i][j + 1].rgbtBlue + original[i + 1][j + 1].rgbtBlue) / 6);
                }
            }
            else if (i > 0 && i < height - 1)
            {
                if (j == 0)
                {
                    image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i + 1][j].rgbtRed + original[i - 1][j].rgbtRed + original[i + 1][j + 1].rgbtRed + original[i][j + 1].rgbtRed + original[i - 1][j + 1].rgbtRed) / 6);
                    image[i][j].rgbtGreen = round((original[i][j].rgbtGreen + original[i + 1][j].rgbtGreen + original[i- 1][j].rgbtGreen + original[i + 1][j + 1].rgbtGreen + original[i][j + 1].rgbtGreen + original[i - 1][j + 1].rgbtGreen) / 6);
                    image[i][j].rgbtBlue = round((original[i][j].rgbtBlue + original[i + 1][j].rgbtBlue + original[i - 1][j].rgbtBlue + original[i + 1][j + 1].rgbtBlue + original[i][j + 1].rgbtBlue + original[i - 1][j + 1].rgbtBlue) / 6);
                }
                else if (j == width - 1)
                {
                    image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i + 1][j].rgbtRed + original[i - 1][j].rgbtRed + original[i + 1][j - 1].rgbtRed + original[i][j - 1].rgbtRed + original[i - 1][j - 1].rgbtRed) / 6);
                    image[i][j].rgbtGreen = round((original[i][j].rgbtGreen + original[i + 1][j].rgbtGreen + original[i- 1][j].rgbtGreen + original[i + 1][j - 1].rgbtGreen + original[i][j - 1].rgbtGreen + original[i - 1][j - 1].rgbtGreen) / 6);
                    image[i][j].rgbtBlue = round((original[i][j].rgbtBlue + original[i + 1][j].rgbtBlue + original[i - 1][j].rgbtBlue + original[i + 1][j - 1].rgbtBlue + original[i][j - 1].rgbtBlue + original[i - 1][j - 1].rgbtBlue) / 6);
                }
                else
                {
                    image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i][j - 1].rgbtRed + original[i][j + 1].rgbtRed + original[i + 1][j - 1].rgbtRed + original[i + 1][j + 1].rgbtRed + original[i + 1][j].rgbtRed + original[i - 1][j - 1].rgbtRed + original[i - 1][j + 1].rgbtRed + original[i - 1][j].rgbtRed) / 9);
                    image[i][j].rgbtGreen = round((original[i][j].rgbtGreen + original[i][j - 1].rgbtGreen + original[i][j + 1].rgbtGreen + original[i + 1][j - 1].rgbtGreen + original[i + 1][j + 1].rgbtGreen+ original[i + 1][j].rgbtGreen + original[i - 1][j - 1].rgbtGreen + original[i - 1][j + 1].rgbtGreen + original[i - 1][j].rgbtGreen) / 9);
                    image[i][j].rgbtBlue = round((original[i][j].rgbtBlue + original[i][j - 1].rgbtBlue + original[i][j + 1].rgbtBlue + original[i + 1][j - 1].rgbtBlue + original[i + 1][j + 1].rgbtBlue + original[i + 1][j].rgbtBlue + original[i - 1][j - 1].rgbtBlue + original[i - 1][j + 1].rgbtBlue + original[i - 1][j].rgbtBlue) / 9);
                }
            }
            else if (i == height - 1)
            {
                if (j == 0)
                {
                    image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i - 1][j].rgbtRed + original[i][j + 1].rgbtRed + original[i - 1][j + 1].rgbtRed) / 4);
                    image[i][j].rgbtGreen = round((original[i][j].rgbtGreen + original[i - 1][j].rgbtGreen + original[i][j + 1].rgbtGreen + original[i - 1][j + 1].rgbtGreen) / 4);
                    image[i][j].rgbtBlue = round((original[i][j].rgbtBlue + original[i - 1][j].rgbtBlue + original[i][j + 1].rgbtBlue + original[i - 1][j + 1].rgbtBlue) / 4);
                }
                else if (j == width - 1)
                {
                    image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i - 1][j].rgbtRed + original[i][j - 1].rgbtRed + original[i - 1][j - 1].rgbtRed) / 4);
                    image[i][j].rgbtGreen = round((original[i][j].rgbtGreen + original[i - 1][j].rgbtGreen + original[i][j - 1].rgbtGreen + original[i - 1][j - 1].rgbtGreen) / 4);
                    image[i][j].rgbtBlue = round((original[i][j].rgbtBlue + original[i - 1][j].rgbtBlue + original[i][j - 1].rgbtBlue + original[i - 1][j - 1].rgbtBlue) / 4);
                }
                else
                {
                    image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i - 1][j].rgbtRed + original[i][j - 1].rgbtRed + original[i - 1][j - 1].rgbtRed + original[i][j + 1].rgbtRed + original[i - 1][j + 1].rgbtRed) / 6);
                    image[i][j].rgbtGreen = round((original[i][j].rgbtGreen + original[i - 1][j].rgbtGreen + original[i][j - 1].rgbtGreen + original[i - 1][j - 1].rgbtGreen + original[i][j + 1].rgbtGreen + original[i - 1][j + 1].rgbtGreen) / 6);
                    image[i][j].rgbtBlue = round((original[i][j].rgbtBlue + original[i - 1][j].rgbtBlue + original[i][j - 1].rgbtBlue + original[i - 1][j - 1].rgbtBlue + original[i][j + 1].rgbtBlue + original[i - 1][j + 1].rgbtBlue) / 6);
                }
            }
        }
    }
}

Answer 1

如果结构RGBTRIPLE的成员具有 integer 类型，则 integer 划分发生在如下行中

image[i][j].rgbtRed = round((original[i][j].rgbtRed + original[i + 1][j].rgbtRed + original[i][j + 1].rgbtRed + original[i + 1][j + 1].rgbtRed) / 4);

并且结果在传递给round() function之前被截断为整数。

除法器应该是像4.0这样的浮点数，而不是像4这样的整数。

如果在应用此更改后法官仍然拒绝您的答案，则应该是由于浮点数的计算错误。 在这种情况下，您应该避免使用浮点数计算，并考虑如何仅使用整数计算来计算所需的值。

Answer 2

MikeCAT 的回答肯定是对的。 作为他建议的替代方案，您可以通过在 integer 除法之前添加一半除数来避免与浮点的转换，例如

image[i][j].rgbtRed = (original[i][j].rgbtRed + … + original[i+1][j+1].rgbtRed + 2) / 4;
…
image[i][j].rgbtRed = (original[i][j].rgbtRed + … + original[i-1][j  ].rgbtRed + 4) / 9;

Answer 3

我想我的解决方案很短

void blur(int height, int width, RGBTRIPLE image[height][width])
{
for(int i = 0; i < height; i++)
{
    for(int j = 0; j < width; j++)
    {
        int avgrgb[3] = {0,0,0}, n = 0;
        
        int a[3][3] = { {i-1, i-1, i-1}, {i, i, i}, {i+1, i+1,i+1} }, b[3][3] = { {j-1, j, j+1}, {j-1, j, j+1}, {j-1, j, j+1} };
        
        for(int x = 0; x < 3; x++)
        {
            for(int y = 0; y < 3; y++)
            {
                if (a[x][y] >= 0 && a[x][y] >= 0)
                {
                    avgrgb[0] += image[a[x][y]][b[x][y]].rgbtRed;
                    avgrgb[1] += image[a[x][y]][b[x][y]].rgbtGreen;
                    avgrgb[2] += image[a[x][y]][b[x][y]].rgbtBlue;
                    n++;
                }
            }
        }
        
        avgrgb[0] /= n;
        avgrgb[1] /= n;
        avgrgb[2] /= n;

        image[i][j].rgbtRed = avgrgb[0];
        image[i][j].rgbtGreen = avgrgb[1];
        image[i][j].rgbtBlue = avgrgb[2];
    }
}
return;
}

Answer 4

您的解决方案是完美的，您只需编写 4.0, 6.0, 9.0 而不是 4,6, 9