Table Of Contents
Table Of Contents

Source code for gluoncv.nn.bbox

# pylint: disable=arguments-differ
"""Bounding boxes operators"""
from __future__ import absolute_import

import numpy as np
from mxnet import gluon


[docs]class NumPyBBoxCornerToCenter(object): """Convert corner boxes to center boxes using numpy. Corner boxes are encoded as (xmin, ymin, xmax, ymax) Center boxes are encoded as (center_x, center_y, width, height) Parameters ---------- split : bool Whether split boxes to individual elements after processing. axis : int, default is -1 Effective axis of the bounding box. Default is -1(the last dimension). Returns ------- A BxNx4 NDArray if split is False, or 4 BxNx1 NDArray if split is True """ def __init__(self, axis=-1, split=False): super(NumPyBBoxCornerToCenter, self).__init__() self._split = split self._axis = axis def __call__(self, x): xmin, ymin, xmax, ymax = np.split(x, 4, axis=self._axis) # note that we do not have +1 here since our nms and box iou does not. # this is different that detectron. width = xmax - xmin height = ymax - ymin x = xmin + width * 0.5 y = ymin + height * 0.5 if not self._split: return np.concatenate((x, y, width, height), axis=self._axis) else: return x, y, width, height
[docs]class BBoxCornerToCenter(gluon.HybridBlock): """Convert corner boxes to center boxes. Corner boxes are encoded as (xmin, ymin, xmax, ymax) Center boxes are encoded as (center_x, center_y, width, height) Parameters ---------- split : bool Whether split boxes to individual elements after processing. axis : int, default is -1 Effective axis of the bounding box. Default is -1(the last dimension). Returns ------- A BxNx4 NDArray if split is False, or 4 BxNx1 NDArray if split is True """ def __init__(self, axis=-1, split=False): super(BBoxCornerToCenter, self).__init__() self._split = split self._axis = axis
[docs] def hybrid_forward(self, F, x): """Hybrid forward""" xmin, ymin, xmax, ymax = F.split(x, axis=self._axis, num_outputs=4) # note that we do not have +1 here since our nms and box iou does not. # this is different that detectron. width = xmax - xmin height = ymax - ymin x = xmin + width * 0.5 y = ymin + height * 0.5 if not self._split: return F.concat(x, y, width, height, dim=self._axis) else: return x, y, width, height
[docs]class BBoxCenterToCorner(gluon.HybridBlock): """Convert center boxes to corner boxes. Corner boxes are encoded as (xmin, ymin, xmax, ymax) Center boxes are encoded as (center_x, center_y, width, height) Parameters ---------- split : bool Whether split boxes to individual elements after processing. axis : int, default is -1 Effective axis of the bounding box. Default is -1(the last dimension). Returns ------- A BxNx4 NDArray if split is False, or 4 BxNx1 NDArray if split is True. """ def __init__(self, axis=-1, split=False): super(BBoxCenterToCorner, self).__init__() self._split = split self._axis = axis
[docs] def hybrid_forward(self, F, x): """Hybrid forward""" x, y, w, h = F.split(x, axis=self._axis, num_outputs=4) hw = w * 0.5 hh = h * 0.5 xmin = x - hw ymin = y - hh xmax = x + hw ymax = y + hh if not self._split: return F.concat(xmin, ymin, xmax, ymax, dim=self._axis) else: return xmin, ymin, xmax, ymax
[docs]class BBoxSplit(gluon.HybridBlock): """Split bounding boxes into 4 columns. Parameters ---------- axis : int, default is -1 On which axis to split the bounding box. Default is -1(the last dimension). squeeze_axis : boolean, default is `False` If true, Removes the axis with length 1 from the shapes of the output arrays. **Note** that setting `squeeze_axis` to ``true`` removes axis with length 1 only along the `axis` which it is split. Also `squeeze_axis` can be set to ``true`` only if ``input.shape[axis] == num_outputs``. """ def __init__(self, axis, squeeze_axis=False, **kwargs): super(BBoxSplit, self).__init__(**kwargs) self._axis = axis self._squeeze_axis = squeeze_axis
[docs] def hybrid_forward(self, F, x): return F.split(x, axis=self._axis, num_outputs=4, squeeze_axis=self._squeeze_axis)
[docs]class BBoxArea(gluon.HybridBlock): """Calculate the area of bounding boxes. Parameters ---------- fmt : str, default is corner Bounding box format, can be {'center', 'corner'}. 'center': {x, y, width, height} 'corner': {xmin, ymin, xmax, ymax} axis : int, default is -1 Effective axis of the bounding box. Default is -1(the last dimension). Returns ------- A BxNx1 NDArray """ def __init__(self, axis=-1, fmt='corner', **kwargs): super(BBoxArea, self).__init__(**kwargs) if fmt.lower() == 'corner': self._pre = BBoxCornerToCenter(split=True) elif fmt.lower() == 'center': self._pre = BBoxSplit(axis=axis) else: raise ValueError("Unsupported format: {}. Use 'corner' or 'center'.".format(fmt))
[docs] def hybrid_forward(self, F, x): _, _, width, height = self._pre(x) width = F.where(width > 0, width, F.zeros_like(width)) height = F.where(height > 0, height, F.zeros_like(height)) return width * height
[docs]class BBoxBatchIOU(gluon.HybridBlock): """Batch Bounding Box IOU. Parameters ---------- axis : int On which axis is the length-4 bounding box dimension. fmt : str BBox encoding format, can be 'corner' or 'center'. 'corner': (xmin, ymin, xmax, ymax) 'center': (center_x, center_y, width, height) offset : float, default is 0 Offset is used if +1 is desired for computing width and height, otherwise use 0. eps : float, default is 1e-15 Very small number to avoid division by 0. """ def __init__(self, axis=-1, fmt='corner', offset=0, eps=1e-15, **kwargs): super(BBoxBatchIOU, self).__init__(**kwargs) self._offset = offset self._eps = eps if fmt.lower() == 'center': self._pre = BBoxCenterToCorner(split=True) elif fmt.lower() == 'corner': self._pre = BBoxSplit(axis=axis, squeeze_axis=True) else: raise ValueError("Unsupported format: {}. Use 'corner' or 'center'.".format(fmt))
[docs] def hybrid_forward(self, F, a, b): """Compute IOU for each batch Parameters ---------- a : mxnet.nd.NDArray or mxnet.sym.Symbol (B, N, 4) first input. b : mxnet.nd.NDArray or mxnet.sym.Symbol (B, M, 4) second input. Returns ------- mxnet.nd.NDArray or mxnet.sym.Symbol (B, N, M) array of IOUs. """ al, at, ar, ab = self._pre(a) bl, bt, br, bb = self._pre(b) # (B, N, M) left = F.broadcast_maximum(al.expand_dims(-1), bl.expand_dims(-2)) right = F.broadcast_minimum(ar.expand_dims(-1), br.expand_dims(-2)) top = F.broadcast_maximum(at.expand_dims(-1), bt.expand_dims(-2)) bot = F.broadcast_minimum(ab.expand_dims(-1), bb.expand_dims(-2)) # clip with (0, float16.max) iw = F.clip(right - left + self._offset, a_min=0, a_max=6.55040e+04) ih = F.clip(bot - top + self._offset, a_min=0, a_max=6.55040e+04) i = iw * ih # areas area_a = ((ar - al + self._offset) * (ab - at + self._offset)).expand_dims(-1) area_b = ((br - bl + self._offset) * (bb - bt + self._offset)).expand_dims(-2) union = F.broadcast_add(area_a, area_b) - i return i / (union + self._eps)
[docs]class BBoxClipToImage(gluon.HybridBlock): """Clip bounding box coordinates to image boundaries. If multiple images are supplied and padded, must have additional inputs of accurate image shape. """ def __init__(self, **kwargs): super(BBoxClipToImage, self).__init__(**kwargs)
[docs] def hybrid_forward(self, F, x, img): """If images are padded, must have additional inputs for clipping Parameters ---------- x: (B, N, 4) Bounding box coordinates. img: (B, C, H, W) Image tensor. Returns ------- (B, N, 4) Bounding box coordinates. """ x = F.maximum(x, 0.0) # window [B, 2] -> reverse hw -> tile [B, 4] -> [B, 1, 4], boxes [B, N, 4] window = F.shape_array(img).slice_axis(axis=0, begin=2, end=None).expand_dims(0) m = F.tile(F.reverse(window, axis=1), reps=(2,)).reshape((0, -4, 1, -1)) return F.broadcast_minimum(x, F.cast(m, dtype='float32'))