まず、実験コード

#include <iostream>
#include <fstream>
using namespace std;

#define Height 256
#define Width 256
#define Size 256


// 计算熵
double Count_Entropy(double* freq) {
	double entropy=0;
	for (int i = 0; i < Size; i++)
	{
		if ((*(freq + i)) != 0) {
			entropy += (*(freq + i)) * log2(1 / (*(freq + i)));
		}
	}
	return entropy;
}

// 计算频率
void Count_freq(double *freq,int *cnt) {
	for (int i = 0; i < Size; i++) {
		*(freq + i) = *(cnt + i) / (double)(Height * Width);
	}
}

// 输出至 .txt
void PrintToTxt(double* freq, ofstream& File) {
	for (int i = 0; i < Size; i++) {
		File <<i<<"\t"<<*(freq+i)<< endl;
	}
}

int main(){
	// 开辟3个width * height的unsigned char型数组
	unsigned char Red[Height][Width] = { 0 }, Green[Height][Width] = { 0 }, Blue[Height][Width] = {};
	// 开辟3个数组用以统计
	int Red_cnt[Size] = { 0 }, Blue_cnt[Size] = { 0 }, Green_cnt[Size] = { 0 };
	// 开辟3个数组用以计算
	double Red_freq[Size] = { 0 }, Blue_freq[Size] = { 0 }, Green_freq[Size] = { 0 };

	// 打开要读出的RGB文件
	ifstream File_in;
	File_in.open("C:\\File_xieyh\\FILE\\down.rgb", ios::in | ios::binary);
	if (!File_in) {
		cout << "Error opening down.rgb" << endl;
		return 0;
	}

	// 打开3个要输出的数据统计文件
	ofstream R_sat, G_sat, B_sat;
	R_sat.open("R_sat.txt", ios::out, ios::trunc);
	G_sat.open("G_sat.txt", ios::out, ios::trunc);
	B_sat.open("B_sat.txt", ios::out, ios::trunc);
	if (!R_sat||!G_sat||!B_sat) {
		cout << "Error opening R_sat.txt||G_sat.txt||B_sat.txt" << endl;
		return 0;
	}

	// 向txt写入抬头
	R_sat << "symbol\tfreq" << endl;
	G_sat << "symbol\tfreq" << endl;
	B_sat << "symbol\tfreq" << endl;

	// 将RGB数据从RGB文件中读出，并分别保存到3个数组中
	for (int i = 0; i <Height; i++) {
		for (int j = 0; j < Width; j++) {
			File_in.read((char*)(*(Blue + i)+j), sizeof(unsigned char));
			Blue_cnt[*(*(Blue + i) + j)]++;
			
			File_in.read((char*)(*(Green + i) + j), sizeof(unsigned char));
			Green_cnt[*(*(Green + i) + j)]++;

			File_in.read((char*)(*(Red + i) + j), sizeof(unsigned char));
			Red_cnt[*(*(Red + i) + j)]++;
		}
	}

	// 计算数据的概率分布和
	Count_freq(Red_freq, Red_cnt);
	Count_freq(Green_freq, Green_cnt);
	Count_freq(Blue_freq, Blue_cnt);

	// 打印至 .txt
	PrintToTxt(Red_freq, R_sat);
	PrintToTxt(Green_freq, G_sat);
	PrintToTxt(Blue_freq, B_sat);

	cout << "已输出至txt" << endl;

	// 计算熵
	double Red_Entropy, Green_Entropy, Blue_Entropy;
	Red_Entropy = Count_Entropy(Red_freq);
	Green_Entropy = Count_Entropy(Green_freq);
	Blue_Entropy = Count_Entropy(Blue_freq);

	// 输出熵
	cout << "Red_Entropy=" << Red_Entropy << endl;
	cout << "Green_Entropy=" << Green_Entropy << endl;
	cout << "Blue_Entropy=" << Blue_Entropy << endl;

	//关闭文件
	File_in.close();
	R_sat.close();
	G_sat.close();
	B_sat.close();

	return 0;
}