# nms¶

paddle.vision.ops. nms ( boxes, iou_threshold=0.3, scores=None, category_idxs=None, categories=None, top_k=None ) [source]

This operator implements non-maximum suppression. Non-maximum suppression (NMS) is used to select one bounding box out of many overlapping bounding boxes in object detection. Boxes with IoU > iou_threshold will be considered as overlapping boxes, just one with highest score can be kept. Here IoU is Intersection Over Union, which can be computed by:

$IoU = \frac{intersection\_area(box1, box2)}{union\_area(box1, box2)}$

If scores are provided, input boxes will be sorted by their scores firstly.

If category_idxs and categories are provided, NMS will be performed with a batched style, which means NMS will be applied to each category respectively and results of each category will be concated and sorted by scores.

If K is provided, only the first k elements will be returned. Otherwise, all box indices sorted by scores will be returned.

Parameters
• boxes (Tensor) – The input boxes data to be computed, it’s a 2D-Tensor with the shape of [num_boxes, 4]. The data type is float32 or float64. Given as [[x1, y1, x2, y2], …], (x1, y1) is the top left coordinates, and (x2, y2) is the bottom right coordinates. Their relation should be 0 <= x1 < x2 && 0 <= y1 < y2.

• iou_threshold (float32, optional) – IoU threshold for determine overlapping boxes. Default value: 0.3.

• scores (Tensor, optional) – Scores corresponding to boxes, it’s a 1D-Tensor with shape of [num_boxes]. The data type is float32 or float64. Default: None.

• category_idxs (Tensor, optional) – Category indices corresponding to boxes. it’s a 1D-Tensor with shape of [num_boxes]. The data type is int64. Default: None.

• categories (List, optional) – A list of unique id of all categories. The data type is int64. Default: None.

• top_k (int64, optional) – The top K boxes who has higher score and kept by NMS preds to consider. top_k should be smaller equal than num_boxes. Default: None.

Returns

1D-Tensor with the shape of [num_boxes]. Indices of boxes kept by NMS.

Return type

Tensor

Examples

import paddle
import numpy as np

boxes = np.random.rand(4, 4).astype('float32')
boxes[:, 2] = boxes[:, 0] + boxes[:, 2]
boxes[:, 3] = boxes[:, 1] + boxes[:, 3]
# [[0.06287421 0.5809351  0.3443958  0.8713329 ]
#  [0.0749094  0.9713205  0.99241287 1.2799143 ]
#  [0.46246734 0.6753201  1.346266   1.3821303 ]
#  [0.8984796  0.5619834  1.1254641  1.0201943 ]]

# [0, 1, 3, 0]

scores = np.random.rand(4).astype('float32')
# [0.98015213 0.3156527  0.8199343  0.874901 ]

categories = [0, 1, 2, 3]
category_idxs = np.random.choice(categories, 4)
# [2 0 0 3]