SIFT-sift.m

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% [image, descriptors, locs] = sift(imageFile)%% This function reads an image and returns its SIFT keypoints.%   Input parameters:%     imageFile: the file name for the image.%%   Returned:%     image: the image array in double format%     descriptors: a K-by-128 matrix, where each row gives an invariant%         descriptor for one of the K keypoints.  The descriptor is a vector%         of 128 values normalized to unit length.%     locs: K-by-4 matrix, in which each row has the 4 values for a%         keypoint location (row, column, scale, orientation).  The %         orientation is in the range [-PI, PI] radians.%% Credits: Thanks for initial version of this program to D. Alvaro and %          J.J. Guerrero, Universidad de Zaragoza (modified by D. Lowe)function [image, descriptors, locs] = sift(imageFile)% Load imageimage = imread(imageFile);% If you have the Image Processing Toolbox, you can uncomment the following  % lines to allow input of color images, which will be converted to grayscale.% if isrgb(image)   % image = rgb2gray(image);% end[rows, cols] = size(image); % Convert into PGM imagefile, readable by "keypoints" executablef = fopen('tmp.pgm', 'w');if f == -1    error('Could not create file tmp.pgm.');endfprintf(f, 'P5\n%d\n%d\n255\n', cols, rows);fwrite(f, image', 'uint8');fclose(f);% Call keypoints executableif isunix    command = '!./sift ';else    command = '!siftWin32 ';endcommand = [command ' <tmp.pgm >tmp.key'];eval(command);% Open tmp.key and check its headerg = fopen('tmp.key', 'r');if g == -1    error('Could not open file tmp.key.');end[header, count] = fscanf(g, '%d %d', [1 2]);if count ~= 2    error('Invalid keypoint file beginning.');endnum = header(1);len = header(2);if len ~= 128    error('Keypoint descriptor length invalid (should be 128).');end% Creates the two output matrices (use known size for efficiency)locs = double(zeros(num, 4));descriptors = double(zeros(num, 128));% Parse tmp.keyfor i = 1:num    [vector, count] = fscanf(g, '%f %f %f %f', [1 4]); %row col scale ori    if count ~= 4        error('Invalid keypoint file format');    end    locs(i, :) = vector(1, :);    [descrip, count] = fscanf(g, '%d', [1 len]);    if (count ~= 128)        error('Invalid keypoint file value.');    end    % Normalize each input vector to unit length    descrip = descrip / sqrt(sum(descrip.^2));    descriptors(i, :) = descrip(1, :);endfclose(g);