（三） 用C/C++读取rgb格式文件数据并分析其概率分布

rgb格式文件并不多见。其存储方式为B G R Y 的数值顺序存储
以下图为例：

将此图的rgb格式文件用FlexHEX打开后是这样的：

其中存储数据的顺序为B G R Y
我们用codeblock编译C++语言文件对其进行分析
代码如下：
#include “iostream”
#include"stdio.h"
#include"math.h"
using namespace std;
double entropy(double freq[256])
{
double entropy = 0;
for (int i = 0; i < 256; i++)
{
if (freq[i] == 0)
continue;
entropy = entropy - freq[i]*log(freq[i])/log(2);//计算BGR的熵
}
return entropy;
}

int main()
{
//图像分辨率为256256，格式为bgr
unsigned char b = new unsigned char[256256];
unsigned char g = new unsigned char[256256];
unsigned char r = new unsigned char[256256];
unsigned char img = new unsigned char[2562563];
FILE* fp = fopen(“E:\大三下\数据压缩\down.rgb”, “rb”);
if (fp == NULL)
cout << “无法读取图像” << endl;
fread(img, sizeof(unsigned char), 2562563, fp);
fclose(fp);
for (int i = 0;i < 256256; i++)
{
b[i] = img[3i];
g[i] = img[3i+1];
r[i] = img[3i+2];
}
//计算分布概率
double freb[256] = {0};
double freg[256] = {0};
double frer[256] = {0};
for (int i = 0; i < 256; i++)
{
int countb = 0, countg = 0, countr = 0;
for (int j = 0; j < 256 * 256; j++)
{
if ((int)b[j] == i)
countb ++;
if ((int)g[j] == i)
countg ++;
if ((int)r[j] == i)
countr++;
}
freb[i] = (double)countb/256/256;
freg[i] = (double)countg/256/256;
frer[i] = (double)countr/256/256;
}
//计算熵
double entropyB = 0, entropyG = 0, entropyR = 0;
entropyB = entropy(freb);
entropyG = entropy(freg);
entropyR = entropy(frer);
//输出txt文件
char s[] = “symbol\tfrequency\n”;
FILE* dataB = fopen(“E:\大三下\数据压缩\b.txt”,“w”);
fprintf(dataB, s);
FILE* dataG = fopen(“E:\大三下\数据压缩\g.txt”,“w”);
fprintf(dataG, s);
FILE* dataR = fopen(“E:\大三下\数据压缩\r.txt”,“w”);
fprintf(dataR, s);
for (int i = 0;i < 256; i++)
{
fprintf(dataB,"%d\t%f\n",i, freb[i]);
fprintf(dataG,"%d\t%f\n",i, freg[i]);
fprintf(dataR,"%d\t%f\n",i, frer[i]);
}
fprintf(dataB,“entropy = %f”,entropyB);
fprintf(dataG,“entropy = %f”,entropyG);
fprintf(dataR,“entropy = %f”,entropyR);
fclose(dataB);
fclose(dataG);
fclose(dataR);
}

最后输出到txt文件中是这样的
将其中的数据导入excel生成概率分布图：