我正在从 BMP 文件中读取像素的 RGB 值，但未获得正确的值

Question

我按照此链接处的代码读取bmp文件中的像素值，以便能够读取像素的RGB值，当我将整个图像作为一种颜色并读取随机像素值时，它们是正确的。在此之后，我尝试制作它，以便函数也会尝试查找有多少独特的颜色，所以我添加了一个不同颜色的框到图像中，但函数仍然只能找到一种颜色。我想知道我是否不知何故没有查看BMP中包含的所有字节，但我不确定这会是怎样的，因为我是新尝试这种东西的。

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，当发现颜色与始终找到的颜色不同但从未输出时，我尝试打印输出。

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，总是在（0,0）处检查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];