我正在从 BMP 文件中读取像素的 RGB 值，但没有得到正确的值

Question

我遵循此链接read pixel value in bmp file 上的代码能够读取像素的 RGB 值，当我将整个图像作为一种颜色并读取随机像素的值时，它们是正确的。在此之后，我尝试制作它，因此该功能也将尝试找出有多少种独特的颜色，因此我在图像中添加了一个具有不同颜色的框，但该功能仍然只能找到一种颜色。我想知道我是否可能没有查看 BMP 中包含的所有字节，但我不确定那会是怎样的，因为我是新手。

为了确保代码没有找到不同颜色的像素但未能将它们添加到唯一像素列表中，我尝试在找到与始终找到但没有输出的颜色不同时打印输出来自它。

struct Color {
int R = -1;
int G = -1;
int B = -1;
};

unsigned char* readBMP(char* filename) {
int i;
FILE* f = fopen(filename, "rb");
unsigned char info[54];
fread(info, sizeof(unsigned char), 54, f);

int width = *(int*)&info[18]; //the reason *(int*) is used here because there's an integer stored at 18 in the array that indicates how wide the BMP is
int height = *(int*)&info[22]; // same reasoning for *(int*)

int size = 3 * width * height;
unsigned char* data = new unsigned char[size];
fread(data, sizeof(unsigned char), size, f);
fclose(f);

// windows has BMP saved as BGR tuples and this switches it to RGB
for(i = 0; i < size; i += 3){
    unsigned char tmp = data[i];
    data[i] = data[i+2];
    data[i+2] = tmp;
}

i = 0; // i is the x value of the pixel that is having its RGB values checked
int j = 0; // j is the y value of the pixel that is having its RGB values checked
unsigned char R = data[3 * (i * width + j)]; // value of R of the pixel at (i,j)
unsigned char G = data[3 * (i * width + j) + 1]; // value of G of the pixel at (i,j)
unsigned char B = data[3 * (i * width + j) + 2]; // value of B of the pixel at (i,j)

std::cout << "value of R is " << int(R);
std::cout << " value of G is " << int(G);
std::cout << " value of B is " << int(B);

Color num_colors[5];
int count;
int z;
int flag;
int iterator;
int sum;
for(count = 0; count < size; count += 1){
    unsigned char R = data[3 * (i * width + j)];
    unsigned char G = data[3 * (i * width + j) + 1];
    unsigned char B = data[3 * (i * width + j) + 2];
    sum = int(R) + int(G) + int(B);
    if(sum != 301) {// 301 is the sum of the RGB values of the color that the program does manage to find
        std::cout << sum;
    }
    flag = 0;
    for(z = 0; z < 5; z += 1){
        if(num_colors[z].R == R && num_colors[z].G == G && num_colors[z].B == B){
            flag = 1;
        }
    }
    if(flag == 1){
        continue;
    }
    iterator = 0;
    while(num_colors[iterator].R != -1){
        iterator += 1;
    }
    num_colors[iterator].R = R;
    num_colors[iterator].G = G;
    num_colors[iterator].B = B;
}

int number = 0;
for(int r = 0; r < 5; r += 1){
    std::cout << "\nValue of R here: " << num_colors[r].R;
    if(num_colors[r].R != -1){
        number += 1;
    }
}
std::cout << "\nNumber of colors in image: " << number;
return data;
}

https://imgur.com/a/dXllIWL 这是我正在使用的图片，所以应该找到两种颜色，但代码只找到红色像素。

Answer 1

您的问题是您总是检查 (0,0) 处的 RGB 值

i = 0; // i is the x value of the pixel that is having its RGB values checked
int j = 0; // j is the y value of the pixel that is having its RGB values checked
...
for(count = 0; count < size; count += 1){
    unsigned char R = data[3 * (i * width + j)];
    unsigned char G = data[3 * (i * width + j) + 1];
    unsigned char B = data[3 * (i * width + j) + 2];

i 和 j 定义了您正在检查的像素的 X 和 Y 位置，但请注意，您永远不会在循环中更改它们。你的循环会一遍又一遍地做同样的事情。您可能想要的是一个双循环，遍历图像中的所有坐标：

   for(int y=0; y<height; y++)
       for(int x=0; x<width; x++){
          unsigned char R = data[3 * (y * width + x) + 0];
          unsigned char G = data[3 * (y * width + x) + 1];
          unsigned char B = data[3 * (y * width + x) + 2];