如何在空间和频率域中的每个尺度和方向创建 64 个 Gabor 特征

通常，Gabor 滤波器，顾名思义，用于过滤图像并提取与过滤方向相同的所有内容。

在这个问题中，您可以看到比此中编写的代码更有效的代码Link

假设 4 个方向上有 16 个尺度的滤波器，因此我们得到 64 个 gabor 滤波器。

scales=[7:2:37]，7x7 到 37x37 以两个像素为步长，所以我们有 7x7, 9x9, 11x11, 13x13, 15x15, 17x17, 19x19, 21x21, 23x23, 25x25, 27x27, 29x29, 31x31, 33 x33, 35x35 和 37x37。

方向=[0, pi/4, pi/2, 3pi/4]。

Gabor滤波器在空间域的方程为：

The equation of Gabor filter in the frequency domain is:

在空间域中：

function [fSiz,filters,c1OL,numSimpleFilters] = init_gabor(rot, RF_siz)    

    image=imread('xxx.jpg');
    image_gray=rgb2gray(image);
    image_gray=imresize(image_gray, [100 100]);
    image_double=double(image_gray);

    rot = [0 45 90 135]; % we have four orientations
                RF_siz    = [7:2:37]; %we get 16 scales (7x7 to 37x37 in steps of two pixels)
                minFS     = 7; % the minimum receptive field
                maxFS     = 37; % the maximum receptive field
                sigma  = 0.0036*RF_siz.^2 + 0.35*RF_siz + 0.18; %define the equation of effective width
                lambda = sigma/0.8; % it the equation of wavelength (lambda)
                G      = 0.3;   % spatial aspect ratio: 0.23 < gamma < 0.92


                numFilterSizes   = length(RF_siz); % we get 16

                numSimpleFilters = length(rot); % we get 4

                numFilters       = numFilterSizes*numSimpleFilters; % we get 16x4 = 64 filters

                fSiz             = zeros(numFilters,1); % It is a vector of size numFilters where each cell contains the size of the filter (7,7,7,7,9,9,9,9,11,11,11,11,......,37,37,37,37)

                filters          = zeros(max(RF_siz)^2,numFilters); % Matrix of Gabor filters of size %max_fSiz x num_filters, where max_fSiz is the length of the largest filter and num_filters the total number of filters. Column j of filters matrix contains a n_jxn_j filter (reshaped as a column vector and padded with zeros).




            for k = 1:numFilterSizes  
                for r = 1:numSimpleFilters
                    theta     = rot(r)*pi/180; % so we get 0, pi/4, pi/2, 3pi/4
                    filtSize  = RF_siz(k); 
                    center    = ceil(filtSize/2);
                    filtSizeL = center-1;
                    filtSizeR = filtSize-filtSizeL-1;
                    sigmaq    = sigma(k)^2;

                    for i = -filtSizeL:filtSizeR
                        for j = -filtSizeL:filtSizeR

                            if ( sqrt(i^2+j^2)>filtSize/2 )
                                E = 0;
                            else
                                x = i*cos(theta) - j*sin(theta);
                                y = i*sin(theta) + j*cos(theta);
                                E = exp(-(x^2+G^2*y^2)/(2*sigmaq))*cos(2*pi*x/lambda(k));
                            end
                            f(j+center,i+center) = E;
                        end
                    end

                    f = f - mean(mean(f));
                    f = f ./ sqrt(sum(sum(f.^2)));
                    p = numSimpleFilters*(k-1) + r;
                    filters(1:filtSize^2,p)=reshape(f,filtSize^2,1);
                    fSiz(p)=filtSize;
                end
            end

            % Rebuild all filters (of all sizes)

            nFilts = length(fSiz);
            for i = 1:nFilts
              sqfilter{i} = reshape(filters(1:(fSiz(i)^2),i),fSiz(i),fSiz(i));

            %if you will use conv2 to convolve an image with this gabor, so you should also add the equation below. But if you will use imfilter instead of conv2, so do not add the equation below.

                    sqfilter{i} = sqfilter{i}(end:-1:1,end:-1:1); %flip in order to use conv2 instead of imfilter (%bug_fix 6/28/2007);

    convv=imfilter(image_double, sqfilter{i}, 'same', 'conv');
    figure;

        imagesc(convv);
        colormap(gray);

                      end