详解目标检测模型的评价指标及代码实现

import numpy as np
import matplotlib.pyplot as plt
class_names = ["car", "pedestrians", "bicycle"]
def draw_PR_curve(predict_scores, eval_labels, name, cls_idx=1):
 """calculate AP and draw PR curve, there are 3 types
    Parameters:
    @all_scores: single test dataset predict scores array, (-1, 3)
    @all_labels: single test dataset predict label array, (-1, 3)
    @cls_idx: the serial number of the AP to be calculated, example: 0,1,2,3...
    """
 # print('sklearn Macro-F1-Score:', f1_score(predict_scores, eval_labels, average='macro'))
 global class_names
    fig, ax = plt.subplots(nrows=1, ncols=1, figsize=(15, 10))
 # Rank the predicted scores from large to small, extract their corresponding index(index number), and generate an array
 idx = predict_scores[:, cls_idx].argsort()[::-1]
 eval_labels_descend = eval_labels[idx]
 pos_gt_num = np.sum(eval_labels == cls_idx) # number of all gt
 predict_results = np.ones_like(eval_labels)
 tp_arr = np.logical_and(predict_results == cls_idx, eval_labels_descend == cls_idx) # ndarray
 fp_arr = np.logical_and(predict_results == cls_idx, eval_labels_descend != cls_idx)
 tp_cum = np.cumsum(tp_arr).astype(float) # ndarray, Cumulative sum of array elements.
 fp_cum = np.cumsum(fp_arr).astype(float)
 precision_arr = tp_cum / (tp_cum + fp_cum) # ndarray
 recall_arr = tp_cum / pos_gt_num
    ap = 0.0
 prev_recall = 0
 for p, r in zip(precision_arr, recall_arr):
      ap += p * (r - prev_recall)
 # pdb.set_trace()
 prev_recall = r
 print("------%s, ap: %f-----" % (name, ap))
 fig_label = '[%s, %s] ap=%f' % (name, class_names[cls_idx], ap)
 ax.plot(recall_arr, precision_arr, label=fig_label)
 ax.legend(loc="lower left")
 ax.set_title("PR curve about class: %s" % (class_names[cls_idx]))
 ax.set(xticks=np.arange(0., 1, 0.05), yticks=np.arange(0., 1, 0.05))
 ax.set(xlabel="recall", ylabel="precision", xlim=[0, 1], ylim=[0, 1])
 fig.savefig("./pr-curve-%s.png" % class_names[cls_idx])
 plt.close(fig)

def voc_ap(rec, prec, use_07_metric=False):
 """ 
    ap = voc_ap(rec, prec, [use_07_metric])
    Compute VOC AP given precision and recall.
    If use_07_metric is true, uses the
    VOC 07 11 point method (default:False).
    """
 if use_07_metric:
 # 11 point metric
        ap = 0.
 for t in np.arange(0., 1.1, 0.1):
 if np.sum(rec >= t) == 0:
                p = 0
 else:
                p = np.max(prec[rec >= t])
            ap = ap + p / 11.
 else:
 # correct AP calculation
 # first append sentinel values at the end
 mrec = np.concatenate(([0.], rec, [1.]))
 mpre = np.concatenate(([0.], prec, [0.]))
 # compute the precision envelope
 for i in range(mpre.size - 1, 0, -1):
 mpre[i - 1] = np.maximum(mpre[i - 1], mpre[i])
 # to calculate area under PR curve, look for points
 # where X axis (recall) changes value
 i = np.where(mrec[1:] != mrec[:-1])[0]
 # and sum (Delta recall) * prec
        ap = np.sum((mrec[i + 1] - mrec[i]) * mpre[i + 1])
 return ap

def parse_rec(filename):
 """ Parse a PASCAL VOC xml file 
 Return : list, element is dict.
    """
    tree = ET.parse(filename)
    objects = []
 for obj in tree.findall('object'):
 obj_struct = {}
 obj_struct['name'] = obj.find('name').text
 obj_struct['pose'] = obj.find('pose').text
 obj_struct['truncated'] = int(obj.find('truncated').text)
 obj_struct['difficult'] = int(obj.find('difficult').text)
 bbox = obj.find('bndbox')
 obj_struct['bbox'] = [int(bbox.find('xmin').text),
 int(bbox.find('ymin').text),
 int(bbox.find('xmax').text),
 int(bbox.find('ymax').text)]
 objects.append(obj_struct)
 return objects
def voc_eval(detpath,
 annopath,
 imagesetfile,
 classname,
 cachedir,
 ovthresh=0.5,
             use_07_metric=False):
 """rec, prec, ap = voc_eval(detpath,
 annopath,
 imagesetfile,
 classname,
                                [ovthresh],
                                [use_07_metric])
    Top level function that does the PASCAL VOC evaluation.
 detpath: Path to detections result file
 detpath.format(classname) should produce the detection results file.
 annopath: Path to annotations file
 annopath.format(imagename) should be the xml annotations file.
 imagesetfile: Text file containing the list of images, one image per line.
 classname: Category name (duh)
 cachedir: Directory for caching the annotations
    [ovthresh]: Overlap threshold (default = 0.5)
    [use_07_metric]: Whether to use VOC07's 11 point AP computation
        (default False)
    """
 # assumes detections are in detpath.format(classname)
 # assumes annotations are in annopath.format(imagename)
 # assumes imagesetfile is a text file with each line an image name
 # cachedir caches the annotations in a pickle file
 # first load gt
 if not os.path.isdir(cachedir):
 os.mkdir(cachedir)
 cachefile = os.path.join(cachedir, '%s_annots.pkl' % imagesetfile)
 # read list of images
 with open(imagesetfile, 'r') as f:
        lines = f.readlines()
 imagenames = [x.strip() for x in lines]
 if not os.path.isfile(cachefile):
 # load annotations
        recs = {}
 for i, imagename in enumerate(imagenames):
            recs[imagename] = parse_rec(annopath.format(imagename))
 if i % 100 == 0:
 print('Reading annotation for {:d}/{:d}'.format(
 i + 1, len(imagenames)))
 # save
 print('Saving cached annotations to {:s}'.format(cachefile))
 with open(cachefile, 'wb') as f:
 pickle.dump(recs, f)
 else:
 # load
 with open(cachefile, 'rb') as f:
 try:
                recs = pickle.load(f)
 except:
                recs = pickle.load(f, encoding='bytes')
 # extract gt objects for this class
 class_recs = {}
 npos = 0
 for imagename in imagenames:
        R = [obj for obj in recs[imagename] if obj['name'] == classname]
 bbox = np.array([x['bbox'] for x in R])
        difficult = np.array([x['difficult'] for x in R]).astype(np.bool)
        det = [False] * len(R)
 npos = npos + sum(~difficult)
 class_recs[imagename] = {'bbox': bbox,
 'difficult': difficult,
 'det': det}
 # read dets
 detfile = detpath.format(classname)
 with open(detfile, 'r') as f:
        lines = f.readlines()
 splitlines = [x.strip().split(' ') for x in lines]
 image_ids = [x[0] for x in splitlines]
    confidence = np.array([float(x[1]) for x in splitlines])
    BB = np.array([[float(z) for z in x[2:]] for x in splitlines])
 nd = len(image_ids)
 tp = np.zeros(nd)
 fp = np.zeros(nd)
 if BB.shape[0] > 0:
 # sort by confidence
 sorted_ind = np.argsort(-confidence)
 sorted_scores = np.sort(-confidence)
        BB = BB[sorted_ind, :]
 image_ids = [image_ids[x] for x in sorted_ind]
 # go down dets and mark TPs and FPs
 for d in range(nd):
            R = class_recs[image_ids[d]]
            bb = BB[d, :].astype(float)
 ovmax = -np.inf
            BBGT = R['bbox'].astype(float)
 if BBGT.size > 0:
 # compute overlaps
 # intersection
 ixmin = np.maximum(BBGT[:, 0], bb[0])
 iymin = np.maximum(BBGT[:, 1], bb[1])
 ixmax = np.minimum(BBGT[:, 2], bb[2])
 iymax = np.minimum(BBGT[:, 3], bb[3])
 iw = np.maximum(ixmax - ixmin + 1., 0.)
 ih = np.maximum(iymax - iymin + 1., 0.)
                inters = iw * ih
 # union
 uni = ((bb[2] - bb[0] + 1.) * (bb[3] - bb[1] + 1.) +
 (BBGT[:, 2] - BBGT[:, 0] + 1.) *
 (BBGT[:, 3] - BBGT[:, 1] + 1.) - inters)
                overlaps = inters / uni
 ovmax = np.max(overlaps)
 jmax = np.argmax(overlaps)
 if ovmax > ovthresh:
 if not R['difficult'][jmax]:
 if not R['det'][jmax]:
 tp[d] = 1.
                        R['det'][jmax] = 1
 else:
 fp[d] = 1.
 else:
 fp[d] = 1.
 # compute precision recall
 fp = np.cumsum(fp)
 tp = np.cumsum(tp)
    rec = tp / float(npos)
 # avoid divide by zero in case the first detection matches a difficult
 # ground truth
 prec = tp / np.maximum(tp + fp, np.finfo(np.float64).eps)
    ap = voc_ap(rec, prec, use_07_metric)
 return rec, prec, ap