为什么 CS50 的滤镜（less）（PSET 4）中的模糊功能没有返回正确的值？

Question

目前卡在 CS50 的 PSET 4 过滤器上较少。为了创建模糊函数，我想出了 9 种可能的情况，其中像素可能出现在图像中（例如，在第一行和第一列中）。但是，当我使用 check50 检查代码时，函数返回的值与预期值不同。我已经多次查看了我的代码，但我不太明白问题出在哪里，并希望有第二双眼睛来帮助我。提前致谢。

#include "helpers.h"
#include <math.h>

// Blur image
void blur(int height, int width, RGBTRIPLE image[height][width])
{
    // Copy 2D image array into a new array to work with
    RGBTRIPLE copy[height][width];
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            copy[i][j] = image[i][j];
        }
    }
    // Determine case and respond accordingly
    for (int i = 0; i < height; i++)
    {
        for (int j = 0; j < width; j++)
        {
            // CASE 1: Pixel is not in 1st/last row AND not in 1st/LAST column
            if (0 < j < width - 1 && 0 < i < height - 1 )
            {
                int R1 = round((copy[i-1][j-1].rgbtRed + copy[i-1][j].rgbtRed + copy[i-1][j+1].rgbtRed + copy[i][j-1].rgbtRed + copy[i][j].rgbtRed + copy[i][j+1].rgbtRed + copy[i+1][j-1].rgbtRed + copy[i+1][j].rgbtRed + copy[i+1][j+1].rgbtRed)/9.0);
                int G1 = round((copy[i-1][j-1].rgbtGreen + copy[i-1][j].rgbtGreen + copy[i-1][j+1].rgbtGreen + copy[i][j-1].rgbtGreen + copy[i][j].rgbtGreen + copy[i][j+1].rgbtGreen + copy[i+1][j-1].rgbtGreen + copy[i+1][j].rgbtGreen + copy[i+1][j+1].rgbtGreen)/9.0);
                int B1 = round((copy[i-1][j-1].rgbtBlue + copy[i-1][j].rgbtBlue + copy[i-1][j+1].rgbtBlue + copy[i][j-1].rgbtBlue + copy[i][j].rgbtBlue + copy[i][j+1].rgbtBlue + copy[i+1][j-1].rgbtBlue + copy[i+1][j].rgbtBlue + copy[i+1][j+1].rgbtBlue)/9.0);
                image[i][j].rgbtRed = R1;
                image[i][j].rgbtGreen = G1;
                image[i][j].rgbtBlue = B1;
            }
            // CASE 2: Pixel in 1st row, 1st column
            else if (i == 0 && j == 0)
            {
                int R2 = round((copy[i][j].rgbtRed + copy[i][j+1].rgbtRed + copy[i+1][j].rgbtRed + copy[i+1][j+1].rgbtRed)/4.0);
                int B2 = round((copy[i][j].rgbtBlue + copy[i][j+1].rgbtBlue + copy[i+1][j].rgbtBlue + copy[i+1][j+1].rgbtBlue)/4.0);
                int G2 = round((copy[i][j].rgbtGreen + copy[i][j+1].rgbtGreen + copy[i+1][j].rgbtGreen + copy[i+1][j+1].rgbtGreen)/4.0);
                image[i][j].rgbtRed = R2;
                image[i][j].rgbtGreen = G2;
                image[i][j].rgbtBlue = B2;
            }
            // CASE 3: Pixel in 1st row, NOT 1ST/LAST COLUMN
            else if (i == 0 && 0 < j < width - 1)
            {
                int R3 = round((copy[i][j-1].rgbtRed + copy[i][j].rgbtRed + copy[i][j+1].rgbtRed + copy[i+1][j-1].rgbtRed + copy[i+1][j].rgbtRed + copy[i+1][j+1].rgbtRed)/6.0);
                int G3 = round((copy[i][j-1].rgbtGreen + copy[i][j].rgbtGreen + copy[i][j+1].rgbtGreen + copy[i+1][j-1].rgbtGreen + copy[i+1][j].rgbtGreen + copy[i+1][j+1].rgbtGreen)/6.0);
                int B3 = round((copy[i][j-1].rgbtBlue + copy[i][j].rgbtBlue + copy[i][j+1].rgbtBlue + copy[i+1][j-1].rgbtBlue + copy[i+1][j].rgbtBlue + copy[i+1][j+1].rgbtBlue)/6.0);
                image[i][j].rgbtRed = R3;
                image[i][j].rgbtGreen = G3;
                image[i][j].rgbtBlue = B3;
            }
            // CASE 4: PIXEL IN 1ST ROW, LAST COLUMN
            else if (i == 0 && j == width - 1)
            {
                int R4 = round((copy[i][j-1].rgbtRed + copy[i][j].rgbtRed + copy[i+1][j].rgbtRed + copy[i+1][j-1].rgbtRed)/4.0);
                int B4 = round((copy[i][j-1].rgbtBlue + copy[i][j].rgbtBlue + copy[i+1][j].rgbtBlue + copy[i+1][j-1].rgbtBlue)/4.0);
                int G4 = round((copy[i][j-1].rgbtGreen + copy[i][j].rgbtGreen + copy[i+1][j].rgbtGreen + copy[i+1][j-1].rgbtGreen)/4.0);
                image[i][j].rgbtRed = R4;
                image[i][j].rgbtGreen = G4;
                image[i][j].rgbtBlue = B4;
            }
            // CASE 5: PIXEL NOT IN 1ST/LAST ROW, IN 1ST COLUMN
            else if (0 < i < height - 1 && j == 0)
            {
                int R5 = round((copy[i-1][j].rgbtRed + copy[i-1][j+1].rgbtRed + copy[i][j].rgbtRed + copy[i][j+1].rgbtRed + copy[i+1][j].rgbtRed + copy[i+1][j+1].rgbtRed)/6.0);
                int G5 = round((copy[i-1][j].rgbtBlue + copy[i-1][j+1].rgbtBlue + copy[i][j].rgbtBlue + copy[i][j+1].rgbtBlue + copy[i+1][j].rgbtBlue + copy[i+1][j+1].rgbtBlue)/6.0);
                int B5 = round((copy[i-1][j].rgbtGreen + copy[i-1][j+1].rgbtGreen + copy[i][j].rgbtGreen + copy[i][j+1].rgbtGreen + copy[i+1][j].rgbtGreen + copy[i+1][j+1].rgbtGreen)/6.0);
                image[i][j].rgbtRed = R5;
                image[i][j].rgbtGreen = G5;
                image[i][j].rgbtBlue = B5;
            }
            // CASE 6: PIXEL IN LAST ROW, 1ST COLUMN
            else if (i == height - 1 && j == 0)
            {
                int R6 = round((copy[i-1][j].rgbtRed + copy[i-1][j+1].rgbtRed + copy[i][j].rgbtRed + copy[i][j+1].rgbtRed)/4.0);
                int B6 = round((copy[i-1][j].rgbtBlue + copy[i-1][j+1].rgbtBlue + copy[i][j].rgbtBlue + copy[i][j+1].rgbtBlue)/4.0);
                int G6 = round((copy[i-1][j].rgbtGreen + copy[i-1][j+1].rgbtGreen + copy[i][j].rgbtGreen + copy[i][j+1].rgbtGreen)/4.0);
                image[i][j].rgbtRed = R6;
                image[i][j].rgbtGreen = G6;
                image[i][j].rgbtBlue = B6;
            }
            // CASE 7: Pixel IN LAST ROW, LAST COLUMN
            else if (i == height - 1 && j == width - 1)
            {
                int R7 = round((copy[i-1][j].rgbtRed + copy[i-1][j-1].rgbtRed + copy[i][j].rgbtRed + copy[i][j-1].rgbtRed)/4.0);
                int B7 = round((copy[i-1][j].rgbtBlue + copy[i-1][j-1].rgbtBlue + copy[i][j].rgbtBlue + copy[i][j-1].rgbtBlue)/4.0);
                int G7 = round((copy[i-1][j].rgbtGreen + copy[i-1][j-1].rgbtGreen + copy[i][j].rgbtGreen + copy[i][j-1].rgbtGreen)/4.0);
                image[i][j].rgbtRed = R7;
                image[i][j].rgbtGreen = G7;
                image[i][j].rgbtBlue = B7;
            }
            // CASE 8: PIXEL IN LAST ROW, NOT LAST / 1ST COLUMN
            else if (i == height - 1 && 0 < j < width - 1)
            {
                int R8 = round((copy[i][j-1].rgbtRed + copy[i][j].rgbtRed + copy[i][j+1].rgbtRed + copy[i-1][j-1].rgbtRed + copy[i-1][j].rgbtRed + copy[i-1][j+1].rgbtRed)/6.0);
                int G8 = round((copy[i][j-1].rgbtGreen + copy[i][j].rgbtGreen + copy[i][j+1].rgbtGreen + copy[i-1][j-1].rgbtGreen + copy[i-1][j].rgbtGreen + copy[i-1][j+1].rgbtGreen)/6.0);
                int B8 = round((copy[i][j-1].rgbtBlue + copy[i][j].rgbtBlue + copy[i][j+1].rgbtBlue + copy[i-1][j-1].rgbtBlue + copy[i-1][j].rgbtBlue + copy[i-1][j+1].rgbtBlue)/6.0);
                image[i][j].rgbtRed = R8;
                image[i][j].rgbtGreen = G8;
                image[i][j].rgbtBlue = B8;
            }
            // CASE 9: PIXEL IN LAST COLUMN, NOT 1ST / LAST ROW
            else if (0 < i < height - 1 && j == width - 1 )
            {
                int R9 = round((copy[i-1][j].rgbtRed + copy[i-1][j-1].rgbtRed + copy[i][j].rgbtRed + copy[i][j-1].rgbtRed + copy[i+1][j].rgbtRed + copy[i+1][j-1].rgbtRed)/6.0);
                int G9 = round((copy[i-1][j].rgbtBlue + copy[i-1][j-1].rgbtBlue + copy[i][j].rgbtBlue + copy[i][j-1].rgbtBlue + copy[i+1][j].rgbtBlue + copy[i+1][j-1].rgbtBlue)/6.0);
                int B9 = round((copy[i-1][j].rgbtGreen + copy[i-1][j-1].rgbtGreen + copy[i][j].rgbtGreen + copy[i][j-1].rgbtGreen + copy[i+1][j].rgbtGreen + copy[i+1][j-1].rgbtGreen)/6.0);
                image[i][j].rgbtRed = R9;
                image[i][j].rgbtGreen = G9;
                image[i][j].rgbtBlue = B9;
            }
        }
    }
}

起初，我认为问题是由于使用相同的变量名称来存储新的 RGB 值，因此我创建了唯一的变量名称来存储 9 种情况中每种情况的 RGB 值（例如 R1 R2 R3 ...）。然而，事实并非如此。

Answer 1

我认为主要问题是关系运算符不能按您希望的方式工作。

具体来说;对于像 0 0 这样的条件我< height 编译器从左到右计算它，如 (0 < i) < height，其中第一部分变为 true 或 false，第二部分与 true 或 false 进行比较，而不是与 i 进行比较（例如 TRUE < height） 。

要解决此问题，您必须在关系运算符之间使用布尔运算符，例如 (0 < i) && （i<高度）。

作为替代方案；您可以删除所有分支并按顺序执行像素；喜欢：

    // Do top left pixel
    // Do middle pixels on top row
    for (int j = 1; j < width-1; j++) {
    }
    // Do top right pixel

    // Do middle rows
    for (int i = 1; i < height-1; i++) {
        // Do pixel on left edge
        // Do middle pixels
        for (int j = 1; j < width-1; j++) {
        }
        // Do pixel on right edge
     }

    // Do bottom left pixel
    // Do middle pixels on bottom row
    for (int j = 1; j < width-1; j++) {
    }
    // Do bottom right pixel