c - cs50 pset4 - 边缘检测过滤器不起作用 - sobel 算子

Question

我编写的以下代码旨在使用 sobel 算子检测像素中的边缘。但是，它无法通过 check50（cs50 提供的工具）给出的所有测试。输出图像也与输入完全相同。

在继续阅读之前，请访问pset 的链接

• 注意： 我应该在要过滤的像素周围形成一个 3x3 网格，以便可以遍历 GX 和 GY 值中的每个值。我用过整数hh并ww做到这一点。

       // Detect edges
        void edges(int height, int width, RGBTRIPLE image[height][width])
        {
            int sqrtRedd;
            int sqrtGreenn;
            int sqrtBluee;
        
        //make copy of image
            RGBTRIPLE copy[height][width];
        
            for(int h = 0; h < height; h++)
            {
                for(int w = 0; w < width; w++)
                {
                    copy[h][w] = image[h][w];
                }
            }
        
        //loop through pixels
            for(int h = 0; h < height; h++)
            {
                for(int w = 0; w < width; w++)
                {
                    int GXred = 0;
                    int GYred = 0;
                    int GXgreen = 0;
                    int GYgreen = 0;
                    int GXblue = 0;
                    int GYblue = 0;
                    
                    for(int hh = -1; hh <= 1; hh++)
                    {
                        for(int ww = -1; ww <= 1; ww++)
                        {
                            if( h + hh >= 0 && h + hh < height && w + ww >= 0 && w + ww < width)
                            {
                                //form 3x3 grid
                            GXred += ww * copy[2 - hh * hh][2 - ww * ww].rgbtRed;
                            GYred += hh * copy[2 - hh * hh][2 - ww * ww].rgbtRed;
     
    
                       
                        GXgreen += ww * copy[2 - hh * hh][2 - ww * ww].rgbtGreen;
                        GYgreen += hh * copy[2 - hh * hh][2 - ww * ww].rgbtGreen;
                        
                        GXblue += ww * copy[2 - hh * hh][2 - ww * ww].rgbtBlue;
                        GXblue += hh * copy[2 - hh * hh][2 - ww * ww].rgbtBlue;
                        
                            }
                        }
                    }
                    
                    int red = round(sqrt(GXred * GXred + GYred * GYred));
                    int green = round(sqrt(GXgreen * GXgreen + GYgreen * GXgreen));
                    int blue = round(sqrt(GXblue * GXblue + GYblue * GYblue));
                    
                    if(red > 225)
                    {
                        red = 225;
                    }
                    
                    else if(green > 225)
                    {
                        green = 225;
                    }
                    
                    else if(blue > 225)
                    {
                        blue = 225
                    }
                    
                    image[h][w].rgbtRed = red;
                    image[h][w].rgbtGreen = green;
                    image[h][w].rgbtBlue = blue;
                    
                }
            }
                
            return;
        }

RGB三元组：

typedef struct
{
    BYTE  rgbtBlue;
    BYTE  rgbtGreen;
    BYTE  rgbtRed;
} __attribute__((__packed__))
RGBTRIPLE;

这些是 check50 给出的错误消息：

    :( edges correctly filters middle pixel
        expected "210 150 60\n", not "143 105 30\n"
    :( edges correctly filters pixel on edge
        expected "213 228 255\n", not "164 144 79\n"
    :( edges correctly filters pixel in corner
        expected "76 117 255\n", not "58 77 64\n"
    :( edges correctly filters 3x3 image
        expected "76 117 255\n21...", not "58 77 64\n164 ..."
    :( edges correctly filters 4x4 image
        expected "76 117 255\n21...", not "58 77 64\n164 ..."

如您所见，输出值与实际值相差甚远，甚至不接近应有的值。问题是：我不知道这些错误是否是由a）我试图从内核中找到 GX 和 GY 值的方式或 b）我应用 sobel 运算符的方式引起的。

我尝试以其他方式（无效）查找 GX 和 GY 值，例如：

                         if(hh == -1)
                         {
                            GYred += copy[h - 1][w + ww].rgbtRed * -1;
                            GYgreen += copy[h - 1][w + ww].rgbtGreen * -1;
                            GYblue += copy[h - 1][w + ww].rgbtBlue * -1;
                         }
                         
                         else if( hh == 0)
                         {
                             GYred += copy[h][w + ww].rgbtRed * 0;
                             GYgreen += copy[h][w + ww].rgbtGreen * 0;
                             GYblue += copy[h][w + ww].rgbtBlue * 0;
                         }
                         
                         else if(hh == 1)
                         {
                             GYred += copy[h + 1][w + ww].rgbtRed * 1;
                             GYgreen += copy[h + 1][w + ww].rgbtGreen * 1;
                             GYblue += copy[h + 1][w + ww].rgbtBlue * 2;
                         }
                         
                         else if(hh == 2)
                         {
                             GYred += copy[h + 2][w + ww].rgbtRed * 2;
                             GYgreen += copy[h + 2][w + ww].rgbtGreen * 2;
                             GYblue += copy[h + 2][w + ww].rgbtBlue * 2;
                         }
                         
    //start setting GX values
                         if(ww == -2)
                         {
                             GXred += copy[h + hh][w - 2].rgbtRed * -2;
                             GXgreen += copy[h + hh][w - 2].rgbtGreen * -2;
                             GXblue += copy[h + hh][w - 2].rgbtBlue * -2;
                         }
                         
                         else if(ww == -1)
                         {
                             GXred += copy[h + hh][w - 1].rgbtRed * -1;
                             GXgreen += copy[h + hh][w - 1].rgbtGreen * -1;
                             GXblue += copy[h + hh][w - 1].rgbtBlue * -1;
                         }
                         
                         else if(ww == 0)
                         {
                             GXred += copy[h + hh][w].rgbtRed * 0;
                             GXgreen += copy[h + hh][w].rgbtGreen * 0;
                             GXblue += copy[h + hh][w].rgbtBlue * 0;
                         }
                         
                         else if(ww == 1)
                         {
                             GXred += copy[h + hh][w + 1].rgbtRed * 1;
                             GXgreen += copy[h + hh][w + 1].rgbtGreen * 1;
                             GXblue += copy[h + hh][w + 1].rgbtBlue * 1;
                         }

我已经在这个 pset 上停留了将近一个星期，所以在这一点上，我不知道还能尝试什么。

标签： ccs50edge-detectionsobel

Answer 1

您有相当多的部分没有真正意义或缺失。

• 您不会在任何地方应用 sobel 因子。仅在 3x3 网格内获取偏移量不会产生正确的值，
• 如果溢出，您只能限制 1 个颜色通道，
• 您限制为 225 而不是 255，
• 你混合了GXblueand GYblue，同样的GXgreenand GYgreen。

我准备了一个应该可以解决问题的新版本。现在测试并使用最初失败的 4x4 图像测试的测试数据。

#include <stdio.h>
#include <math.h>

typedef unsigned char BYTE;

typedef struct
{
    BYTE  rgbtBlue;
    BYTE  rgbtGreen;
    BYTE  rgbtRed;
} __attribute__((__packed__))
RGBTRIPLE;

// Detect edges
void edges(int height, int width, RGBTRIPLE image[height][width])
{
    int sqrtRedd;
    int sqrtGreenn;
    int sqrtBluee;

    //make copy of image
    RGBTRIPLE copy[height][width];
    for(int h = 0; h < height; h++)
    {
        for(int w = 0; w < width; w++)
        {
            copy[h][w] = image[h][w];
        }
    }

    //loop through pixels
    for(int h = 0; h < height; h++)
    {
        for(int w = 0; w < width; w++)
        {
            int GXred = 0;
            int GYred = 0;
            int GXgreen = 0;
            int GYgreen = 0;
            int GXblue = 0;
            int GYblue = 0;
            
            int index = 0;
            int factorsX[] = {-1,  0,  1, -2, 0, 2, -1, 0, 1};
            int factorsY[] = {-1, -2, -1,  0, 0, 0,  1, 2, 1};

            //form 3x3 grid
            for(int hh = -1; hh <= 1; hh++)
            {
                for(int ww = -1; ww <= 1; ww++)
                {
                    int x = w+ww;
                    int y = h+hh;
                    if( y >= 0 && y < height && x >= 0 && x < width)
                    {
                        GXred += factorsX[index] * copy[y][x].rgbtRed;
                        GYred += factorsY[index] * copy[y][x].rgbtRed;

                        GXgreen += factorsX[index] * copy[y][x].rgbtGreen;
                        GYgreen += factorsY[index] * copy[y][x].rgbtGreen;

                        GXblue += factorsX[index] * copy[y][x].rgbtBlue;
                        GYblue += factorsY[index] * copy[y][x].rgbtBlue;
                    }                   
                    index++;
                }
            }

            int red = round(sqrt(GXred * GXred + GYred * GYred));
            int green = round(sqrt(GXgreen * GXgreen + GYgreen * GYgreen));
            int blue = round(sqrt(GXblue * GXblue + GYblue * GYblue));

            if(red > 255)
            {
                red = 255;
            }
            if(green > 255)
            {
                green = 255;
            }
            if(blue > 255)
            {
                blue = 255;
            }

            image[h][w].rgbtRed = red;
            image[h][w].rgbtGreen = green;
            image[h][w].rgbtBlue = blue;
        }
    }

    return;
}

int main(void)
{
    RGBTRIPLE test_4x4[4][4] = {
        {{0, 10, 25}, {0, 10, 30}, {40, 60, 80}, {50, 60, 80}},
        {{20, 30, 90}, {30, 40, 100}, {80, 70, 90}, {80, 80, 90}},
        {{20, 20, 40}, {30, 10, 30}, {50, 40, 10}, {50, 40, 100}},
        {{50, 20, 40}, {50, 20, 40}, {50, 40, 80}, {50, 40, 80}},
    };

    edges(4, 4, test_4x4);
    for(int h = 0; h < 4; h++)
    {
        for(int w = 0; w < 4; w++)
        {
            printf("%d %d %d\n", test_4x4[h][w].rgbtBlue, test_4x4[h][w].rgbtGreen, test_4x4[h][w].rgbtRed);
        }
    }

    return 0;
}