一、简介
1 Retinex理论
Retinex理论始于Land和McCann于20世纪60年代作出的一系列贡献,其基本思想是人感知到某点的颜色和亮度并不仅仅取决于该点进入人眼的绝对光线，还和其周围的颜色和亮度有关。Retinex这个词是由视网膜(Retina)和大脑皮层(Cortex)两个词组合构成的.Land之所以设计这个词，是为了表明他不清楚视觉系统的特性究竟取决于此两个生理结构中的哪一个，抑或是与两者都有关系。
Land的Retinex模型是建立在以下的基础之上的：
（1）真实世界是无颜色的，我们所感知的颜色是光与物质的相互作用的结果。我们见到的水是无色的，但是水膜—肥皂膜却是显现五彩缤纷，那是薄膜表面光干涉的结果；
（2）每一颜色区域由给定波长的红、绿、蓝三原色构成的；
（3）三原色决定了每个单位区域的颜色。Retinex 理论的基本内容是物体的颜色是由物体对长波（红）、中波（绿）和短波（蓝）光线的反射能力决定的，而不是由反射光强度的绝对值决定的；物体的色彩不受光照非均性的影响，具有一致性，即Retinex理论是以色感一致性（颜色恒常性）为基础的。如下图所示，观察者所看到的物体的图像S是由物体表面对入射光L反射得到的，反射率R由物体本身决定，不受入射光L变化。
Retinex理论的基本假设是原始图像S是光照图像L和反射率图像R的乘积,即可表示为下式的形式：
基于Retinex的图像增强的目的就是从原始图像S中估计出光照L，从而分解出R，消除光照不均的影响，以改善图像的视觉效果,正如人类视觉系统那样。在处理中，通常将图像转至对数域，即
从而将乘积关系转换为和的关系：
Retinex方法的核心就是估测照度L，从图像S中估测L分量，并去除L分量，得到原始反射分量R，即：
函数 f(x) 实现对照度L的估计（可以去这么理解，实际很多都是直接估计r分量）。
2 Retinex理论的理解
如果大家看论文，那么在接下去的篇幅当中，肯定会介绍两个经典的Retinex算法：基于路径的Retinex以及基于中心/环绕Retinex。在介绍两个经典的Retinex算法之前，我先来讲一点个人的理解，以便第一次接触该理论的朋友能够更快速地理解。当然，如果我的理解有问题，也请大家帮忙指出。
Retinex理论就我理解，与降噪类似，该理论的关键就是合理地假设了图像的构成。如果将观察者看到的图像看成是一幅带有乘性噪声的图像，那么入射光的分量就是一种乘性的，相对均匀，且变换缓慢的噪声。Retinex算法所做的就是合理地估计图像中各个位置的噪声，并除去它。
在极端情况下，我们大可以认为整幅图像中的分量都是均匀的，那么最简单的估计照度L的方式就是在将图像变换到对数域后对整幅图像求均值。因此，我设计了以下算法来验证自己的猜想，流程如下：
（1） 将图像变换到对数域
（2） 归一化去除加性分量
（3） 对步骤3得到的结果求指数，反变换到实数域
二、源代码
function varargout = MainForm(varargin)
% MAINFORM MATLAB code for MainForm.fig
% MAINFORM, by itself, creates a new MAINFORM or raises the existing
% singleton*.
%
% H = MAINFORM returns the handle to a new MAINFORM or the handle to
% the existing singleton*.
%
% MAINFORM('CALLBACK',hObject,eventData,handles,...) calls the local
% function named CALLBACK in MAINFORM.M with the given input arguments.
%
% MAINFORM('Property','Value',...) creates a new MAINFORM or raises the
% existing singleton*. Starting from the left, property value pairs are
% applied to the GUI before MainForm_OpeningFcn gets called. An
% unrecognized property name or invalid value makes property application
% stop. All inputs are passed to MainForm_OpeningFcn via varargin.
%
% *See GUI Options on GUIDE's Tools menu. Choose "GUI allows only one
% instance to run (singleton)".
%
% See also: GUIDE, GUIDATA, GUIHANDLES
% Edit the above text to modify the response to help MainForm
% Last Modified by GUIDE v2.5 5-Apr-2021 17:16:36
% Begin initialization code - DO NOT EDIT
gui_Singleton = 1;
gui_State = struct('gui_Name', mfilename, ...
'gui_Singleton', gui_Singleton, ...
'gui_OpeningFcn', @MainForm_OpeningFcn, ...
'gui_OutputFcn', @MainForm_OutputFcn, ...
'gui_LayoutFcn', [] , ...
'gui_Callback', []);
if nargin && ischar(varargin{1})
gui_State.gui_Callback = str2func(varargin{1});
end
if nargout
[varargout{1:nargout}] = gui_mainfcn(gui_State, varargin{:});
else
gui_mainfcn(gui_State, varargin{:});
end
% End initialization code - DO NOT EDIT
% --- Executes just before MainForm is made visible.
function MainForm_OpeningFcn(hObject, eventdata, handles, varargin)
% This function has no output args, see OutputFcn.
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% varargin command line arguments to MainForm (see VARARGIN)
% Choose default command line output for MainForm
handles.output = hObject;
handles.Img1 = 0;%
handles.Img2 = 0;
% Update handles structure
guidata(hObject, handles);
% UIWAIT makes MainForm wait for user response (see UIRESUME)
% uiwait(handles.figure1);
% --- Outputs from this function are returned to the command line.
function varargout = MainForm_OutputFcn(hObject, eventdata, handles)
% varargout cell array for returning output args (see VARARGOUT);
% hObject handle to figure
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Get default command line output from handles structure
varargout{1} = handles.output;
% --------------------------------------------------------------------
function File_Callback(hObject, eventdata, handles)
% hObject handle to File (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% --------------------------------------------------------------------
function FileOpen_Callback(hObject, eventdata, handles)
% hObject handle to FileOpen (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% 打开
warning off all;
% 载入图像
[FileName,PathName,FilterIndex] = uigetfile({'*.jpg;*.tif;*.png;*.gif', ...
'所有图像文件';...
'*.*','所有文件' },'载入图像',...
'.\images\\sweden_input.jpg');
if isequal(FileName, 0) || isequal(PathName, 0)
return;
end
InitFig(hObject, handles);
Img1 = imread(fullfile(PathName, FileName));
axes(handles.axes1);
imshow(Img1, []);
handles.Img1 = Img1;
handles.Img2 = 0;
guidata(hObject, handles);
% --------------------------------------------------------------------
function Exist_Callback(hObject, eventdata, handles)
% hObject handle to Exist (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
close();
% --------------------------------------------------------------------
function About_Callback(hObject, eventdata, handles)
% hObject handle to About (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
msgbox('低对比度图像增强系统，全局及局部直方图均衡化和基于RETINEX理论图像对比度增强算法', '提示信息');
function edit1_Callback(hObject, eventdata, handles)
% hObject handle to edit1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% Hints: get(hObject,'String') returns contents of edit1 as text
% str2double(get(hObject,'String')) returns contents of edit1 as a double
% --- Executes during object creation, after setting all properties.
function edit1_CreateFcn(hObject, eventdata, handles)
% hObject handle to edit1 (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles empty - handles not created until after all CreateFcns called
% Hint: edit controls usually have a white background on Windows.
% See ISPC and COMPUTER.
if ispc && isequal(get(hObject,'BackgroundColor'), get(0,'defaultUicontrolBackgroundColor'))
set(hObject,'BackgroundColor','white');
end
% --------------------------------------------------------------------
function ImageDeFog_Callback(hObject, eventdata, handles)
% hObject handle to ImageDeFog (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% --------------------------------------------------------------------
function ColorSpaceDeFog_Callback(hObject, eventdata, handles)
% hObject handle to ColorSpaceDeFog (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% --------------------------------------------------------------------
function RetinexDeFog_Callback(hObject, eventdata, handles)
% hObject handle to RetinexDeFog (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
if isequal(handles.Img1, 0)
msgbox('请载入图像！', '提示信息');
return;
end
Img2 = RemoveFogByRetinex(handles.Img1, 0);
axes(handles.axes2); imshow(Img2, []);
handles.Img2 = Img2;
guidata(hObject, handles);
set(handles.textInfo, 'String', ...
'基于RETINEX理论图像对比度增强算法。');
% --------------------------------------------------------------------
function help_Callback(hObject, eventdata, handles)
% hObject handle to help (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% --------------------------------------------------------------------
function Flow_Callback(hObject, eventdata, handles)
% hObject handle to Flow (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
str = '低对比度图像增强系统，首先载入图像并显示，然后选择对比度增强算法，最后可以观察直方图对比效果。';
msgbox(str, '提示信息');
% --------------------------------------------------------------------
function SaveGUI_Callback(hObject, eventdata, handles)
% hObject handle to SaveGUI (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% 截图
SnapImage();
% --------------------------------------------------------------------
function SaveResult_Callback(hObject, eventdata, handles)
% hObject handle to SaveResult (see GCBO)
% eventdata reserved - to be defined in a future version of MATLAB
% handles structure with handles and user data (see GUIDATA)
% 保存
if isequal(handles.Img2, 0)
msgbox('请进行对比度增强处理！', '提示信息');
return;
end
三、运行结果
四、备注
版本：2014a
完整代码或代写加1564658423