Draw labels name (#9496)

* Draw labels name

Draw labels name next to corresponding bounding boxes when the mapping of id to names is specified.

* Update detection.py

* Update detection.py
Fixed missing variable declaration
Fixing lint issues

python/mxnet/image/detection.py

@@ -803,7 +803,7 @@ def check_label_shape(self, label_shape):
             raise ValueError(msg)
 
     def draw_next(self, color=None, thickness=2, mean=None, std=None, clip=True,
-                  waitKey=None, window_name='draw_next'):
+                  waitKey=None, window_name='draw_next', id2labels=None):
         """Display next image with bounding boxes drawn.
 
         Parameters
@@ -822,6 +822,8 @@ def draw_next(self, color=None, thickness=2, mean=None, std=None, clip=True,
             Hold the window for waitKey milliseconds if set, skip ploting if None
         window_name : str
             Plot window name if waitKey is set.
+        id2labels : dict
+            Mapping of labels id to labels name.
 
         Returns
         -------
@@ -889,6 +891,17 @@ def draw_next(self, color=None, thickness=2, mean=None, std=None, clip=True,
                     y2 = int(label[i, 4] * height)
                     bc = np.random.rand(3) * 255 if not color else color
                     cv2.rectangle(image, (x1, y1), (x2, y2), bc, thickness)
+                    if id2labels is not None:
+                        cls_id = int(label[i, 0])
+                        if cls_id in id2labels:
+                            cls_name = id2labels[cls_id]
+                            text = "{:s}".format(cls_name)
+                            font = cv2.FONT_HERSHEY_SIMPLEX
+                            font_scale = 0.5
+                            text_height = cv2.getTextSize(text, font, font_scale, 2)[0][1]
+                            tc = (255, 255, 255)
+                            tpos = (x1 + 5, y1 + text_height + 5)
+                            cv2.putText(image, text, tpos, font, font_scale, tc, 2)
                 if waitKey is not None:
                     cv2.imshow(window_name, image)
                     cv2.waitKey(waitKey)