2020.3.9读入一个24bitRGB文件（以down.rgb为例，其分辨率为256*256），输出该数据文件中R、G、B三个分量（各8bit表示）的概率分布示意图（类似下图）和熵。

2020.3.9读入一个24bitRGB文件（以down.rgb为例，其分辨率为256*256），输出该数据文件中R、G、B三个分量（各8bit表示）的概率分布示意图（类似下图）和熵。

#include "stdafx.h"
#include <stdio.h>
#include<stdlib.h>
#include<malloc.h>
#include<math.h>
using namespace std;
int main()
{
    FILE* photo;
    FILE* Bsat;
    FILE* Gsat;
    FILE* Rsat;
    const int width = 256;
    const int height = 256;
    fopen_s(&photo, "down.rgb", "rb");//打开要读出的RGB文件（以“rb”方式打开）
    fopen_s(&Bsat, "B_sat.txt", "w");//打开3个要输出的数据统计文件（以“w”方式打开，可命名为R_sat.txt等）
    fopen_s(&Gsat, "G_sat.txt", "w");
    fopen_s(&Rsat, "R_sat.txt", "w");
    unsigned char* buffer = NULL;
    buffer= (unsigned char*)malloc(sizeof(unsigned char) * 3 * width * height);
    fread(buffer,sizeof(unsigned char), 3 * width * height, photo);
    unsigned char B[width * height] ={ 0 };//开辟3个width*height的unsigned char型数组
    unsigned char G[width * height] ={ 0 };
    unsigned char R[width * height] ={ 0 };
    int nB = 0;
    int nG = 0;
    int nR = 0;
    //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 <3*width*height; i++)
    {
        if (i % 3 == 0)
        {
             B[nB]= *(buffer+i);
             nB++;
        }
        else if(i % 3 == 1)
        {
             G[nG]= *(buffer + i);
             nG++;
        }
        else if (i % 3 == 2)
        {
             R[nR]= *(buffer + i);
             nR++;
        }
    }
     //计算数据的概率分布
   int numB[256] = { 0 };
   double freqB[256] = { 0 };
   for (int i = 0; i < 256;i++)
    {
        for (int j = 0; j < width* height; j++)
        {
             if (i == B[j])
             {
                 numB[i]++;
             }
        }
        freqB[i]= double(numB[i]) / (width *height);
    }
    int numG[256] = { 0 };
    double freqG[256] = { 0 };
    for (int i = 0; i < 256;i++)
    {
        for (int j = 0; j < width* height; j++)
        {
             if (i == G[j])
             {
                 numG[i]++;
             }
        }
        freqG[i]= double(numG[i]) / (width *height);
    }
    int numR[256] = { 0 };
    double freqR[256] = { 0 };
    for (int i = 0; i < 256;i++)
    {
        for (int j = 0; j < width* height; j++)
        {
             if (i == R[j])
             {
                 numR[i]++;
             }
        }
        freqR[i]= double(numR[i]) / (width *height);
    }
    //计算熵
    double HB = 0;
    double HG = 0;
    double HR = 0;
    for (int i = 0; i < 256;i++)
    {
        if (freqB[i] != 0)
        {
         double a=2;
         HB= HB - freqB[i] * log(freqB[i]) / log(a); 
        }
        if (freqG[i] != 0)
        {
            double a=2;
            HG= HG - freqG[i] * log(freqG[i]) / log(a);
        }
        if (freqR[i] != 0)
        {
            double a=2;
            HR= HR - freqR[i] * log(freqR[i]) / log(a);
        }
     }
    printf("B的熵是%f\n",HB);
    printf("G的熵是%f\n",HG);
    printf("R的熵是%f\n",HR);
    //将这些数据写入3个数据统计txt文件中。Txt文件的写入方式如下所示（每行的两个数据用tab分开)
    fprintf(Bsat,"symbol\tfreq\n"); 
    fprintf(Gsat,"symbol\tfreq\n"); 
    fprintf(Rsat,"symbol\tfreq\n");
    for (int i = 0; i < 256;i++)
    {
        fprintf(Bsat,"%d\t%f\n",i,freqB[i]);
        fprintf(Gsat,"%d\t%f\n", i,freqG[i]);
        fprintf(Rsat,"%d\t%f\n", i,freqR[i]);
    }
    free(buffer);
    fclose(photo);
    fclose(Bsat);
    fclose(Gsat);
    fclose(Rsat);
    system("pause");
    return 0;
    }

运行结果如下图
R的熵:7.23
G的熵:7.18
B的熵:6.86

输出RGB统计文件

在Excel里将这3个txt文件打开即可生成统计图。