function I=imgaussian(I,sigma,siz) % IMGAUSSIAN filters an 1D, 2D color/greyscale or 3D image with an % Gaussian filter. This function uses for filtering IMFILTER or if % compiled the fast  mex code imgaussian.c . Instead of using a % multidimensional gaussian kernel, it uses the fact that a Gaussian % filter can be separated in 1D gaussian kernels. % % J=IMGAUSSIAN(I,SIGMA,SIZE) % % inputs, %   I: The 1D, 2D greyscale/color, or 3D input image with %           data type Single or Double %一维、二维或是三维的输入图像 %   SIGMA: The sigma used for the Gaussian kernel %标准差 %   SIZE: Kernel size (single value) (default: sigma*6) % 默认的高斯核大小是sigma*6 % outputs, %   J: The gaussian filtered image %输出滤波后的图像 % note, compile the code with: mex imgaussian.c -v % % example, %   I = im2double(imread('peppers.png')); %   figure, imshow(imgaussian(I,10)); % % Function is written by D.Kroon University of Twente (September 2009) if(~exist('siz','var')), siz=sigma*6; end if(sigma>0)     % Make 1D Gaussian kernel     x=-ceil(siz/2):ceil(siz/2);     H = exp(-(x.^2/(2*sigma^2)));     H = H/sum(H(:));%归一化的一步     % Filter each dimension with the 1D Gaussian kernels\     if(ndims(I)==1)         I=imfilter(I,H, 'same' ,'replicate');     elseif(ndims(I)==2)         Hx=reshape(H,[length(H) 1]);         Hy=reshape(H,[1 length(H)]);         I=imfilter(imfilter(I,Hx, 'same' ,'replicate'),Hy, 'same' ,'replicate');     elseif(ndims(I)==3)         if(size(I,3)<4) % Detect if 3D or color image             Hx=reshape(H,[length(H) 1]);             Hy=reshape(H,[1 length(H)]);             for k=1:size(I,3)                 I(:,:,k)=imfilter(imfilter(I(:,:,k),Hx, 'same' ,'replicate'),Hy, 'same' ,'replicate');             end         else             Hx=reshape(H,[length(H) 1 1]);             Hy=reshape(H,[1 length(H) 1]);             Hz=reshape(H,[1 1 length(H)]);             I=imfilter(imfilter(imfilter(I,Hx, 'same' ,'replicate'),Hy, 'same' ,'replicate'),Hz, 'same' ,'replicate');         end     else         error('imgaussian:input','unsupported input dimension');     end end

先是对行进行卷积，再是对列进行卷积。