数据压缩第三次作业

作业3：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。

MATLAB代码
clc;
close all;
clear all;

file1=fopen(“down.rgb”);
X=fread(file1);%读入文件
L=length(X);
R=zeros(256,1);
G=zeros(256,1);
B=zeros(256,1);
for i=1:L
if mod(i,3)==0
R(X(i)+1)=R(X(i)+1)+1;
elseif mod(i,3)==2
G(X(i)+1)=G(X(i)+1)+1;
elseif mod(i,3)==1
B(X(i)+1)=B(X(i)+1)+1;
end
end%用被3除取余数的方法判断是哪一个分量
plot(0:255,R,‘R’);
hold on;
plot(0:255,G,‘G’);
hold on;
plot(0:255,B,‘B’);

MATLAB运行结果

C++代码

#include<stdio.h>
#include<iostream>
#include<math.h>
using namespace std;
const int width = 256;
const int height = 256;

int main()
{
	const int size = width * height * 3;
	FILE *p;
	if ((p = fopen("down.rgb", "rb")) == NULL)
		cout << "file not opened."<<endl;
	else
		cout << "file opened."<<endl;//判断是否打开文件
	unsigned char a[size];
	unsigned char R[width * height] = { 0 };
	unsigned char G[width * height] = { 0 };
	unsigned char B[width * height] = { 0 };
	fread(a, sizeof(unsigned char),size, p);
	int x = 0;
	int y = 0;
	int z = 0;
	for (int i = 0; i < width * height * 3; i++)
	{
		if (i % 3 == 0)
		{
			B[x] = a[i];
			x++;
		}
		else if (i % 3 == 1)
		{
			G[y] = a[i];
			y++;
		}
		else if (i % 3 == 2)
		{
			R[z] = a[i];
			z++;
		}
	}//用被3除求余数的方法判断是RGB哪个分量
	int RT[256] = { 0 };
	int GT[256] = { 0 };
	int BT[256] = { 0 };
	for (int i = 0; i < 256; i++)
	{
		for (int j = 0; j < width * height; j++)
		{
			if (i == R[j])
				RT[i]++;
			if (i == G[j])
				GT[i]++;
			if (i == B[j])
				BT[i]++;
		}
	}//统计各分量出现的次数
	double RF[256] = { 0 };
	double GF[256] = { 0 };
	double BF[256] = { 0 };
	for (int i = 0; i < 256; i++) {
		RF[i] = double(RT[i]) / (width * height);
		GF[i] = double(GT[i]) / (width * height);
		BF[i] = double(BT[i]) / (width * height);
	}//计算各分量的频率
	FILE *r;
	FILE *g;
	FILE *b;
	if ((r = fopen("r.txt", "w")) == NULL)
		cout<<"file not opened."<<endl;
	else
		cout<<"flie opened."<<endl;
	if ((g = fopen("g.txt", "w")) == NULL)
		cout << "file not opened."<<endl;
	else
		cout << "flie opened." << endl;
	if ((b = fopen("b.txt", "w")) == NULL)
		cout << "file not opened."<<endl;
	else
		cout << "flie opened." << endl;//创建txt文件用来存放各分量数据
	fprintf(r, "symbol\tfrequency\n");
	for (int i = 0; i < 256; i++)
	{
		fprintf(r, "%d\t%f\n", i, RF[i]);
	}
	fprintf(g, "symbol\tfrequency\n");
	for (int i = 0; i < 256; i++)
	{
		fprintf(g, "%d\t%f\n", i, GF[i]);
	}
	fprintf(b, "symbol\tfrequency\n");
	for (int i = 0; i < 256; i++)
	{
		fprintf(b, "%d\t%f\n", i, BF[i]);
	}//写入各分量数据
	double HR = 0;
	double HG = 0;
	double HB = 0;
	for (int i = 0; i < 256; i++) {
		if (RF[i] != 0)
			HR = HR - RF[i] * log(RF[i]) / log(2);
		if (GF[i] != 0)
			HG = HG - GF[i] * log(GF[i]) / log(2);
		if (BF[i] != 0)
			HB = HB - BF[i] * log(BF[i]) / log(2);
	}//计算各分量的熵值
	cout << "H(R)=" << HR <<endl;
	cout << "H(G)=" << HG << endl;
	cout << "H(B)=" << HB << endl;
	fclose(p);
	fclose(r);
	fclose(g);
	fclose(b);
	return 0;
}

C++运行结果