均匀分布产生高斯分布

简介

上图像处理课的小作业，顺便复习概率论！！

这里只用了三种方法，未完待续。。。

方法和证明

已经写成word了，不想再打一遍了awsl。

逆变换法

Box-Muller算法

拒绝采样

代码

逆变换代码

clc;
clear;

% 验证高斯噪声--------------
ep = 1e-3;  %间隔
x = -4 : ep : 4;
num = length(x);
U = rand(1, num);
gaussian = @(u) sqrt(2) * erfinv(u);	%高斯分布的逆累积分布函数
y = gaussian(2 * U - 1);
[f, xi] = ksdensity(y, x);				%绘制概率分布
% 作图
figure(1);
plot(x, f);


% 添加高斯噪声--------------
img = imread('lena.bmp');
Nvar = [0 50];	% 均值0，标准差50
rate = 0.5;		% 50%的区域加噪声
img_processed = add_Guassian_noise(img, Nvar, rate);
% 原图
figure(2);
subplot(1, 2, 1);
imshow(img);
title('src');
% 处理后
subplot(1, 2, 2);
imshow(img_processed);
title('dst');

function dst = add_Guassian_noise(src, Nvar, rate)
% src --> raw img to be processed
% Nvar --> [mean, std]
% rate --> the rate of noise
	[r, c] = size(src);
	src = double(src);
	flag = (rand(r,c) > rate);
	U = rand(r, c);
	noise = Nvar(2) * sqrt(2) * erfinv(2 * U - 1) + Nvar(1);
	dst = src + noise .* flag;
	dst = uint8(dst);
	
end

Box-Muller算法代码

clc;
clear;

% 验证高斯噪声---------------
ep = 1e-3;  %间隔
x = -4 : ep : 4;
num = length(x);
U1 = rand(1, num);
U2 = rand(1, num);
y = sqrt(-2 * log(U1)) .* cos(2*pi*U2);		%Box-Muller公式
[f, xi] = ksdensity(y, x);
figure(1);
plot(x, f);

% 添加高斯噪声--------------
img = imread('lena.bmp');
Nvar = [0 50];		% 均值0，标准差50
rate = 0.5;			% 50%的区域加噪声
img_processed = add_Gaussian_noise(img, Nvar, rate);
% 作图
figure(2);
subplot(1, 2, 1);
imshow(img);
title('src');

subplot(1, 2, 2);
imshow(img_processed);
title('dst');

function dst = add_Gaussian_noise(src, Nvar, rate)
% src --> raw img to be processed
% Nvar --> [mean, std]
% rate --> the rate of noise
	[r, c] = size(src);
	src = double(src);
	flag = (rand(r,c) > rate);
	U1 = rand(r, c);
	U2 = rand(r, c);
	noise = Nvar(2) * sqrt(-2 * log(U1)) .* cos(2 * pi * U2) + Nvar(1);
	dst = src + noise .* flag;
	dst = uint8(dst);
	
end

拒绝采样代码

clc;
clear;

% 检验高斯分布------------
ep = 1e-3;
x = -5 : ep : 5;	%five sigma
top = 4 * 1 / 10;	%由于均匀分布U~(-5,5)，则p=0.1；但高斯分布最大值0.4，因此k取4。
sample_num = 1e5;	%采样点1e5个
U = rand(1, sample_num) * 10 - 5;
gaussian = @(x) 1/sqrt(2*pi) * exp(-x.^2 / 2);
sample_id = (rand(1, sample_num) * top) <= gaussian(U);		%接受的id
sample = U(sample_id);
[f, xi] = ksdensity(sample, x);
figure(1);
plot(x, f);

% 添加高斯噪声--------------
img = imread('lena.bmp');
Nvar = [0 50];
rate = 0.5;
img_processed = add_Guassian_noise(img, Nvar, rate);
% 作图
figure(2);
subplot(1, 2, 1);
imshow(img);
title('src');

subplot(1, 2, 2);
imshow(img_processed);
title('dst');

function dst = add_Guassian_noise(src, Nvar, rate)
% src --> raw img to be processed
% Nvar --> [mean, std]
% rate --> the rate of noise
	[r, c] = size(src);
	src = double(src);
	flag = (rand(r,c) < rate);
    sample_num = r * c;	%每次取样r*c个，得到接受的个数n
    noise = [];
    top = 4 * 1 / 10;
    while(length(noise) < sample_num)	%取样n达到r*c后退出循环
        U = 10 * rand(1, sample_num) - 5;
        gau = 1/sqrt(2*pi) * exp(-U.^2 / 2);
        sample_id = (rand(1, sample_num) * top <= gau);
        noise = [noise U(sample_id)];
    end
    noise = noise(1, 1:sample_num);
    noise = reshape(noise, [r, c]);
	noise = Nvar(2) * noise + Nvar(1);
	dst = src + noise .* flag;
	dst = uint8(dst);
end

效果

检验

算法效果

引用

1. https://blog.csdn.net/renwudao24/article/details/44463489
2. https://www.jianshu.com/p/cb916e1ba399
3. https://blog.csdn.net/libing_zeng/article/details/81842245?depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1&utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1

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