目标检测中绘制矩形框

1. 利用matplotlib.pyplot 画矩形框

from matplotlib import pyplot as plt

plt.Rectangle( )参数：

plt.Rectangle(self, xy, width, height, angle=0.0, **kwargs)
#可选参数： fill : bool, optional (whether to fill the rect)
edgecolor: mpl color spec;  linewidth: float or None

第一个参数是矩形左上角点坐标 tuple (x,y)，第二个参数是矩形宽，第三个参数是矩形高

示例：

import matplotlib.pyplot as plt
fig = plt.figure()
ax = fig.add_subplot(1,1,1)
rect = plt.Rectangle((0.1,0.1), 0.5, 0.3, fill=False, edgecolor = 'red',linewidth=1)
ax.add_patch(rect)
plt.show()

rect1.jpg

补充，matplotlib中的图和子图

在使用pyplot进行绘制图形时，是对当前的 figure 或者 axes 进行操作，所以需要先取得需要进行操作的子图，然后利用plt.plot()进行绘图，默认plt.plot( )会在最近的一个图上进行绘制

获得当前的图： plt.gcf() 获得当前的子图: plt.gca()

2. 目标检测中绘制 bounding boxes

参数 Args：
img:    (~numpy.ndarray) in RGB format with shape (3, height, width)
bbox:   (~numpy.ndarray) shape in (R, 4), R is the number of bboxes
label:  (~numpy.ndarray) An integer array of shape R (R, )
score:  (~numpy.ndarray) A float array of shape (R, ), indicating the confidence of predicting
ax:     (matplotlib.axes.Axes): visualization is displayed on this axis, if "None", new one
Returns:    ~matplotlib.axes.Axes

3. 函数 vis_bbox(img, bbox, label=None, score=None, ax=None) 原始链接

def vis_bbox(img, bbox, label=None, score=None, ax=None):
  label_names = list(VOC_BBOX_LABEL_NAMES) + ['bg']
  # add for index `-1`
  if label is not None and not len(bbox) == len(label):
      raise ValueError('The length of label must be same as that of bbox')
  if score is not None and not len(bbox) == len(score):
      raise ValueError('The length of score must be same as that of bbox')

  # Returns newly instantiated matplotlib.axes.Axes object if ax is None
  ax = vis_image(img, ax=ax)

  # If there is no bounding box to display, visualize the image and exit.
  if len(bbox) == 0:
      return ax

  for i, bb in enumerate(bbox):
      xy = (bb[1], bb[0])
      height = bb[2] - bb[0]
      width = bb[3] - bb[1]
      ax.add_patch(plot.Rectangle(
          xy, width, height, fill=False, edgecolor='red', linewidth=2))

      caption = list()

      if label is not None and label_names is not None:
          lb = label[i]
            if not (-1 <= lb < len(label_names)):  # modfy here to add backgroud
              raise ValueError('No corresponding name is given')
          caption.append(label_names[lb])
      if score is not None:
          sc = score[i]
          caption.append('{:.2f}'.format(sc))

      if len(caption) > 0:
          ax.text(bb[1], bb[0],
                  ': '.join(caption),
                  style='italic',
                  bbox={'facecolor': 'white', 'alpha': 0.5, 'pad': 0})
  return ax