Casey Barnette

Notre Dame Harris corners

get_features

For this part of the project we were tasked with creating a feature vector from our interest points. I did a simplified version of sift. I took the gradient of the image and then for a window around the interest points I created a histogram based on the magnitude and direction of the gradient in a 4x4 cell. I did this for each 4x4 cell in the surrounding window. The code for that is shown below. I initially tried to add a scale invariance by normalizing my histogram along the dominant orientation; however, this proved to be ineffective. After the feature vector is created from the histograms I raise it to a small power and then normalize the vector. Sift features brought me from 43% accuracy to 80%

    for j = 1:feature_width/4
        for k=1:feature_width/4
            cWindowDir = feature_window_dir(((j-1)*4) + 1:4*j, ((k-1)*4)+1:4*k);
            cWindowMag = feature_window_mag(4*(j-1)+1:4*j, 4*(k-1)+1:4*k);
            h = zeros(8,1);
            dirFlat = reshape(cWindowDir, [], 1);
            %disp(size(dirFlat));
            magFlat = reshape(cWindowMag, [], 1);
            for v = 1:size(dirFlat, 1)
                [cY, cX] = ind2sub([4 4], v);
                cY = ((j-1)*4)+cY;
                cX = ((k-1)*4)+cX;
                degrees = wrapTo360(atand(dirFlat(v)));
                d_idx = ceil(degrees/45) + 1;
                if d_idx == 9
                    d_idx = 1;
                end
                h(d_idx) = h(d_idx) + (magFlat(v)*g(cY, cX));
            end
            fVec = [fVec; h];
        end

match_feature

This was perhaps the easiest part. For this part I took the euclidean distance for every combination of vectors and found the 2 closest for any given feature. I added the index of the nearest neighbor and the feature I was looking at to the list and then added the confidence value of nn2/nn1. Lastly the values were sorted based on the confidence. This means that the higher confidence values are at the beginning of the list

Results