双边滤波基于小波变换的多尺度自适应THZ增强双边滤波器的MATLAB仿真

Posted 2022-03-28 fpga&matlab

1.软件版本

MATLAB2021a
2.本算法理论知识

        提出了一种”基于小波变换的多尺度自适应双边滤波器“算法。

        其对应的算法流程如下所示：

 

       下面，我们从理论上限介绍一下这里所采用的改进后的算法。

第一：多尺度图像的自适应双边滤波

        这个部分，是我们这里所需要研究的创新的算法，这里重点从理论上介绍一下。

首先通过图像亮度，将图像区分为前景图和背景图。

       这里，我们主要通过二值话处理，进行图像的前景和背景的区分，这个部分的理论为：

 这里，门限T的计算，我们主要通过matlab自带的一个函数获得，这个函数会根据每个图像自动计算出门限T。

graythresh

对于的代码为：

 然后分别对前景和背景进行sigma参数的自适应调整。

       这里，sigma的计算公式为：

       

 这里，我们根据上面的背景前景，做如下的设置。

     这里，我们分别对前景和背景下乘以系数K1和K2，其中根据亮度分布（亮的为背景、暗的为物体）来确定BF的各像素的两个sigma值，让亮区域平滑更多（选用大sigma），暗区域平滑偏小（小sigma）。

3.核心代码

% Pre-process input and select appropriate filter.
function B = bfilter2(A,w,sigma)

% Verify that the input image exists and is valid.
if ~exist('A','var') || isempty(A)
   error('Input image A is undefined or invalid.');
end
if ~isfloat(A) || ~sum([1,3] == size(A,3)) || ...
      min(A(:)) < 0 || max(A(:)) > 1
   error(['Input image A must be a double precision ',...
          'matrix of size NxMx1 or NxMx3 on the closed ',...
          'interval [0,1].']);      
end

% Verify bilateral filter window size.
if ~exist('w','var') || isempty(w) || ...
      numel(w) ~= 1 || w < 1
   w = 5;
end
w = ceil(w);

% Verify bilateral filter standard deviations.
if ~exist('sigma','var') || isempty(sigma) || ...
      numel(sigma) ~= 2 || sigma(1) <= 0 || sigma(2) <= 0
   sigma = [3 0.1];
end

% Apply either grayscale or color bilateral filtering.
if size(A,3) == 1
   B = bfltGray(A,w,sigma(1),sigma(2));
else
   B = bfltColor(A,w,sigma(1),sigma(2));
end


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Implements bilateral filtering for grayscale images.
function B = bfltGray(A,w,sigma_d,sigma_r)

% Pre-compute Gaussian distance weights.
[X,Y] = meshgrid(-w:w,-w:w);
G = exp(-(X.^2+Y.^2)/(2*sigma_d^2));

% Create waitbar.
h = waitbar(0,'Applying bilateral filter...');
set(h,'Name','Bilateral Filter Progress');

% Apply bilateral filter.
dim = size(A);
B = zeros(dim);
for i = 1:dim(1)
   for j = 1:dim(2)
      
         % Extract local region.
         iMin = max(i-w,1);
         iMax = min(i+w,dim(1));
         jMin = max(j-w,1);
         jMax = min(j+w,dim(2));
         I = A(iMin:iMax,jMin:jMax);
      
         % Compute Gaussian intensity weights.
         H = exp(-(I-A(i,j)).^2/(2*sigma_r^2));
      
         % Calculate bilateral filter response.
         F = H.*G((iMin:iMax)-i+w+1,(jMin:jMax)-j+w+1);
         B(i,j) = sum(F(:).*I(:))/sum(F(:));
               
   end
   waitbar(i/dim(1));
end

% Close waitbar.
close(h);


%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Implements bilateral filter for color images.
function B = bfltColor(A,w,sigma_d,sigma_r)

% Convert input sRGB image to CIELab color space.
if exist('applycform','file')
   A = applycform(A,makecform('srgb2lab'));
else
   A = colorspace('Lab<-RGB',A);
end

% Pre-compute Gaussian domain weights.
[X,Y] = meshgrid(-w:w,-w:w);
G = exp(-(X.^2+Y.^2)/(2*sigma_d^2));

% Rescale range variance (using maximum luminance).
sigma_r = 100*sigma_r;

% Create waitbar.
h = waitbar(0,'Applying bilateral filter...');
set(h,'Name','Bilateral Filter Progress');

% Apply bilateral filter.
dim = size(A);
B = zeros(dim);
for i = 1:dim(1)
   for j = 1:dim(2)
      
         % Extract local region.
         iMin = max(i-w,1);
         iMax = min(i+w,dim(1));
         jMin = max(j-w,1);
         jMax = min(j+w,dim(2));
         I = A(iMin:iMax,jMin:jMax,:);
      
         % Compute Gaussian range weights.
         dL = I(:,:,1)-A(i,j,1);
         da = I(:,:,2)-A(i,j,2);
         db = I(:,:,3)-A(i,j,3);
         H = exp(-(dL.^2+da.^2+db.^2)/(2*sigma_r^2));
      
         % Calculate bilateral filter response.
         F = H.*G((iMin:iMax)-i+w+1,(jMin:jMax)-j+w+1);
         norm_F = sum(F(:));
         B(i,j,1) = sum(sum(F.*I(:,:,1)))/norm_F;
         B(i,j,2) = sum(sum(F.*I(:,:,2)))/norm_F;
         B(i,j,3) = sum(sum(F.*I(:,:,3)))/norm_F;
                
   end
   waitbar(i/dim(1));
end

% Convert filtered image back to sRGB color space.
if exist('applycform','file')
   B = applycform(B,makecform('lab2srgb'));
else  
   B = colorspace('RGB<-Lab',B);
end

% Close waitbar.
close(h);

4.操作步骤与仿真结论

 

 

5.参考文献

  A25-09
6.完整源码获得方式

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