RGB文件三通道分量的熵计算

一、实验内容

编程实现RGB文件三通道分量的熵计算。

该测试文件分辨率为256256，数据格式为每个像素占用3字节，BGRBGR…保存。拿到文件可以先计算一下文件大小是否为宽高*3字节。

计算公式：

二、代码实现

先从test.rgb中读取rgb分量，再计算各分量出现的次数，由此计算概率密度，按照熵的计算公式计算出各分量的熵值。

采用C++语言。

注意：提取rgb分量时要按照BGR的顺序提取。

#pragma warning(disable:4996);	//防止编译时不允许使用fopen函数
#include
#include
#include
using namespace std;

int main()
{
	FILE* fp = fopen("C:\\Users\\26617\\Desktop\\数据压缩exe1\\exe1\\test.rgb", "rb");	//打开该文件
	double h = 256;	//高为256
	double w = 256;	//宽为256
	unsigned char* r = (unsigned char*)malloc(256 * 256 * sizeof(unsigned char));	//分配r、g、b分量和buffer的空间
	unsigned char* g = (unsigned char*)malloc(256 * 256 * sizeof(unsigned char));
	unsigned char* b = (unsigned char*)malloc(256 * 256 * sizeof(unsigned char));
	unsigned char* buffer = (unsigned char*)malloc(256 * 256 * 3*sizeof(unsigned char));
	fread(buffer, sizeof(unsigned char), 256 * 256 * 3, fp);	//将文件数据读入

	double pr[256] = { 0 };	//存放rgb概率
	double pg[256] = { 0 };
	double pb[256] = { 0 };
	double rnum[256] = { 0 };	//存放rgb数量
	double gnum[256] = { 0 };
	double bnum[256] = { 0 };
	double sr = 0;	//存放rgb熵值
	double sg = 0;
	double sb = 0;
	int i, j;

	//分别提取rgb分量
	for (i = 0, j = 0; i < 256 * 256 * 3; i = i + 3, j++)
	{
		b[j] = buffer[i];
		g[j] = buffer[i + 1];
		r[j] = buffer[i + 2];
	}

	//计算rgb分量各数值出现的次数
	for (i = 0; i < 256; i++)
	{
		for (j = 0; j < 256 * 256; j++)
		{
			if (r[j] == i)
			{
				rnum[i]++;
			}
			if (g[j] == i)
			{
				gnum[i]++;
			}
			if (b[j] == i)
			{
				bnum[i]++;
			}
		}
	}

	//计算rgb分量概率密度
	for (i = 0; i < 256; i++)
	{
		pr[i] = rnum[i] / double(h * w);
		pg[i] = gnum[i] / double(h * w);
		pb[i] = bnum[i] / double(h * w);
	}

	//计算rgb熵值
	for (i = 0; i < 256; i++)
	{
		if (pr[i] != 0)
		{
			sr += (-1) * pr[i] * (log(pr[i]) / log(2.0));
		}
		if (pg[i] != 0)
		{
			sg += (-1) * pg[i] * (log(pg[i]) / log(2.0));
		}
		if (pb[i] != 0)
		{
			sb += (-1) * pb[i] * (log(pb[i]) / log(2.0));
		}
	}

	cout << "r的熵值为" << sr << endl;
	cout << "g的熵值为" << sg << endl;
	cout << "b的熵值为" << sb << endl;

	return 0;
}

三、实验结果