我正在从BMP文件读取像素的RGB值，但没有获得正确的值

Question

我按照此链接上的代码读取bmp文件中的像素值，从而能够读取像素的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，我尝试制作该函数，以便该函数还将尝试查找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，但该函数仍然只能找到一种颜色。 我想知道是否也许我不以某种方式查看BMP中包含的所有字节，但是我不确定如何尝试，因为我是新手。

为了确保代码没有找到不同的彩色像素，但是没有将它们添加到唯一像素列表中，我尝试在发现一种不同于始终找到的颜色但没有任何输出的颜色时打印输出。

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，因此应该找到两种颜色，但是代码只能找到红色像素。

Answer 1

您的问题是您始终检查（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定义了要检查的像素的X和Y位置，但请注意，您永远不要在循环中更改像素位置。 您的循环将一遍又一遍地执行相同的操作。 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];