自动色阶算法用于图像增强，去雾等，其思想去掉像素值最高的比例，去掉像素值最低的一些比例，然后在将图像的其余像素值进行线性映射或者伽马校正至[0, 255]区间。如下图，在图像处理中是不是很熟悉?!

本文主要参考人在旅途的博客，采用matlab语言实现，算法不在详细叙述，在此代码留做备注。http://www.cnblogs.com/Imageshop/archive/2011/11/13/2247614.html。

以下是程序代码：

function imDst = autolevel(varargin)

[I,lowCut,highCut] =parse_inputs(varargin{:});

[hei,wid,~] = size(I);

PixelAmount = wid * hei;

if size(I,3)==3

[HistRed,~] = imhist(I(:,:,1));

[HistGreen,~] = imhist(I(:,:,2));

[HistBlue,~] = imhist(I(:,:,3));

CumRed = cumsum(HistRed);

CumGreen = cumsum(HistGreen);

CumBlue = cumsum(HistBlue);

minR =find(CumRed>=PixelAmount*lowCut,1,'first');

minG = find(CumGreen>=PixelAmount*lowCut,1,'first');

minB =find(CumBlue>=PixelAmount*lowCut,1,'first');

maxR =find(CumRed>=PixelAmount*(1-highCut),1,'first');

maxG =find(CumGreen>=PixelAmount*(1-highCut),1,'first');

maxB = find(CumBlue>=PixelAmount*(1-highCut),1,'first');

RedMap = linearmap(minR,maxR);

GreenMap = linearmap(minG,maxG);

BlueMap = linearmap(minB,maxB);

imDst = zeros(hei,wid,3,'uint8');

imDst(:,:,1) = RedMap (I(:,:,1));

imDst(:,:,2) = GreenMap(I(:,:,2));

imDst(:,:,3) = BlueMap(I(:,:,3));

else

HistGray = imhist(I(:,:));

CumGray = cumsum(HistRed);

minGray =find(CumGray>=PixelAmount*lowCut,1,'first');

maxGray =find(CumGray>=PixelAmount*(1-highCut),1,'first');

GrayMap = linearmap(minGray,maxGray);

imDst = zeros(hei,wid,'uint8');

imDst(:,:,1) = GrayMap (I(:,:));

end

%--------------------------------------------------------------------

function map = linearmap(low,high)

map = [0:1:255];

for i=0:255

if(i

map(i+1) = 0;

elseif (i>high)

map(i+1) = 255;

else

map(i+1) =uint8((i-low)/(high-low)*255);

end

end

%-------------------------------------------------------------------

function [I,lowCut,highCut] = parse_inputs(varargin)

narginchk(1,3)

I = varargin{1};

validateattributes(I,{'double','logical','uint8','uint16','int16','single'},{},...

mfilename,'Image',1);

if nargin == 1

lowCut = 0.005;

highCut = 0.005;

elseif nargin == 3

lowCut = varargin{2};

highCut = varargin{3};

else

error(message('images:im2double:invalidIndexedImage','single, or logical.'));

end

测试驱动代码：

I = imread('bikes1.jpg');

Out = autolevel(I,0.005,0.005);

imshow([I Out])

测试样例：

个人感觉：

自动色阶用来做去雾，还是最为稳定的，虽然现在有很多种其他增强方法，例如暗通道去雾，优化对比度去雾，基于Color-Lines的去雾，但是这些算法还不是很稳定，当先验知识失效时，处理失真比较严重。顺便一提的是，美图秀秀的一键去雾即是采用此方法。