非极大值抑制

冷不防 2022-08-09 11:54 148阅读 0赞

用于滑动窗口后处理：

优先选择得分高的候选位置，排除与已选窗口重叠的窗口

求两个矩形框相交：

分别求最大左上角点和最小右下角点，后者大于前者，两点确定的矩形框即为相交部分。

function top = nms_face(boxes,overlap)
    % Non-maximum suppression.
    % Greedily select high-scoring detections and skip detections
    % that are significantly covered by a previously selected detection.
    
    if nargin < 2
        overlap = 0.5;
    end
    
    N = length(boxes);
    
    if isempty(boxes)
        top = [];
    else
        numpart = size(boxes(1).xy,1);
        
        % throw away boxes with low score if there are too many candidates
        if N > 30000
            s = [boxes.s];
            [vals, I] = sort(s);
            boxes = boxes(I(end-29999:end));
        end
        N = min(30000,N);
        
        x1 = zeros(N,1);
        y1 = zeros(N,1);
        x2 = zeros(N,1);
        y2 = zeros(N,1);
        area = zeros(N,1);
        for nb = 1:N
            if numpart==1
                x1(nb) = boxes(nb).xy(1);
                y1(nb) = boxes(nb).xy(2);
                x2(nb) = boxes(nb).xy(3);
                y2(nb) = boxes(nb).xy(4);
            else
                x1(nb) = min(boxes(nb).xy(:,1));
                y1(nb) = min(boxes(nb).xy(:,2));
                x2(nb) = max(boxes(nb).xy(:,3));
                y2(nb) = max(boxes(nb).xy(:,4));
            end
            area(nb) = (x2(nb)-x1(nb)+1) * (y2(nb)-y1(nb)+1);
        end
        
        s = [boxes.s];
        [vals, I] = sort(s);
        pick = [];
        while ~isempty(I)
            last = length(I);
            i = I(last);
            pick = [pick; i];
            suppress = [last];
          
            j = I(1:last-1);
            xx1 = max(x1(i), x1(j));
            yy1 = max(y1(i), y1(j));
            xx2 = min(x2(i), x2(j));
            yy2 = min(y2(i), y2(j));
            
            w = xx2-xx1+1;
            w(w<0) = 0;
            h = yy2-yy1+1;
            h(h<0) = 0;
            
            inter = w.*h;
            o1 = inter ./ area(j);
            o2 = inter / area(i);
            idx =  (find((o1 > overlap) | (o2 > overlap)));
            suppress = [suppress ; idx];
            
            I(suppress) = [];
        end
        top = boxes(pick);
    end