Documentation>vl_demo_dsift

# Source code for ``vl_demo_dsift.m

This file is located in the ``toolbox/demo folder in VLFeat package.

    % VL_DEMO_DSIFT Demo: DSIFT

    randn('state',0) ;
    rand('state',0) ;

    % read a test image
    I = imread(fullfile(vl_root,'data','roofs1.jpg')) ;
    I = single(vl_imdown(rgb2gray(I))) ;

    % --------------------------------------------------------------------
    %                                                      Basic benchmark
    % --------------------------------------------------------------------

    binSize = 4 ; % bin size in pixels
    magnif = 3 ; % bin size / keypoint scale

    elaps_dsift = [] ;
    elaps_dsift_fast = [] ;
    err_dsift = [] ;
    err_dsift_fast = [] ;

    binSizeRange = [3 4 5 6] ;
    for wi = 1:length(binSizeRange)
      binSize = binSizeRange(wi) ;
      scale = binSize / magnif ;

      tic ;
      [f, d] = vl_dsift(vl_imsmooth(I, sqrt(scale.^2 - .25)), ...
                        'size', binSize, ...
                        'step', 2, ...
                        'bounds', [20,20,210,140], ...
                        'floatdescriptors', ...
                        'verbose') ;
      elaps_dsift(wi) = toc ;

      tic ;
      [f, dfast] = vl_dsift(vl_imsmooth(I, sqrt(scale.^2 - .25)), ...
                            'size', binSize, ...
                            'step', 2, ...
                            'bounds', [20,20,210,140], ...
                            'floatdescriptors', ...
                            'fast', ...
                            'verbose') ;
      elaps_dsift_fast(wi) = toc ;

      numKeys = size(f, 2) ;
      f_ = [f ; ones(1, numKeys) * scale ; zeros(1, numKeys)] ;

      tic ;
      [f_, d_] = vl_sift(I, ...
                         'magnif', magnif, ...
                         'frames', f_, ...
                         'firstoctave', -1, ...
                         'levels', 5, ...
                         'floatdescriptors') ;
      elaps_sift(wi) = toc ;

      err_dsift(wi)      = mean(mean(abs(d     - d_)) ./ mean(d_)) * 100 ;
      err_dsift_fast(wi) = mean(mean(abs(dfast - d_)) ./ mean(d_)) * 100 ;
    end

    figure(1) ; clf ; title('Descriptor  SIFT') ;
    plot(binSizeRange, [err_dsift ; err_dsift_fast]', 'linewidth', 3) ;
    legend('DSIFT', 'DSIFT fast') ;
    ylabel('Approx error (%)') ;
    xlabel('binSize parameter') ;
    grid on ;
    axis square ;

    figure(2) ; clf ; title('Speedup on regular SIFT') ;
    plot(binSizeRange, ...
         [elaps_sift ./ elaps_dsift ; ...
          elaps_sift ./ elaps_dsift_fast ; ...
          elaps_sift ./ elaps_sift], 'linewidth', 3) ;
    legend('DSIFT', 'DSIFT fast', 'SIFT') ;
    ylabel('Speedup') ;
    xlabel('binSize parameter') ;
    grid on ;
    axis square ;

    figure(1) ; vl_demo_print('dsift_accuracy') ;
    figure(2) ; vl_demo_print('dsift_speedup') ;