解释一下这段代码function [params, bg_area, fg_area, area_resize_factor] = initializeAllAreas(im, params) % we want a regular frame surrounding the object avg_dim = sum(params.target_sz)/2; % size from which we extract features bg_area = round(params.target_sz + avg_dim); % pick a "safe" region smaller than bbox to avoid mislabeling fg_area = round(params.target_sz - avg_dim * params.inner_padding); % saturate to image size if(bg_area(2)>size(im,2)), bg_area(2)=size(im,2)-1; end if(bg_area(1)>size(im,1)), bg_area(1)=size(im,1)-1; end % make sure the differences are a multiple of 2 (makes things easier later in color histograms) bg_area = bg_area - mod(bg_area - params.target_sz, 2); fg_area = fg_area + mod(bg_area - fg_area, 2); % Compute the rectangle with (or close to) params.fixedArea and % same aspect ratio as the target bbox area_resize_factor = sqrt(params.fixed_area/prod(bg_area)); params.norm_bg_area = round(bg_area * area_resize_factor); % Correlation Filter (HOG) feature space % It smaller that the norm bg area if HOG cell size is > 1 params.cf_response_size = floor(params.norm_bg_area / params.hog_cell_size); % given the norm BG area, which is the corresponding target w and h? norm_target_sz_w = 0.75*params.norm_bg_area(2) - 0.25*params.norm_bg_area(1); norm_target_sz_h = 0.75*params.norm_bg_area(1) - 0.25*params.norm_bg_area(2); % norm_target_sz_w = params.target_sz(2) * params.norm_bg_area(2) / bg_area(2); % norm_target_sz_h = params.target_sz(1) * params.norm_bg_area(1) / bg_area(1); params.norm_target_sz = round([norm_target_sz_h norm_target_sz_w]); % distance (on one side) between target and bg area norm_pad = floor((params.norm_bg_area - params.norm_target_sz) / 2); radius = min(norm_pad); % norm_delta_area is the number of rectangles that are considered. % it is the "sampling space" and the dimension of the final merged resposne % it is squared to not privilege any particular direction params.norm_delta_area = (2*radius+1) * [1, 1]; % Rectangle in which the integral images are computed. % Grid of rectangles ( each of size norm_target_sz) has size norm_delta_area. params.norm_pwp_search_area = params.norm_target_sz + params.norm_delta_area - 1; end

这段代码是一个目标跟踪算法中的初始化函数，主要作用是初始化背景区域、前景区域、目标尺寸等参数。首先根据目标大小计算出平均尺寸，然后用它来扩展背景区域和缩小前景区域。接下来根据图像大小对背景区域进行截断，然后将背景区域和前景区域调整为尺寸差为偶数。然后根据设定的固定区域面积和目标宽高比计算出缩放因子和规范化背景区域的大小。根据HOG特征单元大小计算出相关滤波器响应图的大小，然后根据缩放后的背景区域大小计算出对应的目标大小。最后根据目标大小和背景区域大小计算出采样区域大小和积分图计算的矩形区域。