HaMeR / mmpose /datasets /pipelines /top_down_transform.py
geopavlakos's picture
Initial commit
d7a991a
raw
history blame
28.8 kB
# Copyright (c) OpenMMLab. All rights reserved.
import cv2
import numpy as np
from mmpose.core.post_processing import (affine_transform, fliplr_joints,
get_affine_transform, get_warp_matrix,
warp_affine_joints)
from mmpose.datasets.builder import PIPELINES
@PIPELINES.register_module()
class TopDownRandomFlip:
"""Data augmentation with random image flip.
Required keys: 'img', 'joints_3d', 'joints_3d_visible', 'center' and
'ann_info'.
Modifies key: 'img', 'joints_3d', 'joints_3d_visible', 'center' and
'flipped'.
Args:
flip (bool): Option to perform random flip.
flip_prob (float): Probability of flip.
"""
def __init__(self, flip_prob=0.5):
self.flip_prob = flip_prob
def __call__(self, results):
"""Perform data augmentation with random image flip."""
img = results['img']
joints_3d = results['joints_3d']
joints_3d_visible = results['joints_3d_visible']
center = results['center']
# A flag indicating whether the image is flipped,
# which can be used by child class.
flipped = False
if np.random.rand() <= self.flip_prob:
flipped = True
if not isinstance(img, list):
img = img[:, ::-1, :]
else:
img = [i[:, ::-1, :] for i in img]
if not isinstance(img, list):
joints_3d, joints_3d_visible = fliplr_joints(
joints_3d, joints_3d_visible, img.shape[1],
results['ann_info']['flip_pairs'])
center[0] = img.shape[1] - center[0] - 1
else:
joints_3d, joints_3d_visible = fliplr_joints(
joints_3d, joints_3d_visible, img[0].shape[1],
results['ann_info']['flip_pairs'])
center[0] = img[0].shape[1] - center[0] - 1
results['img'] = img
results['joints_3d'] = joints_3d
results['joints_3d_visible'] = joints_3d_visible
results['center'] = center
results['flipped'] = flipped
return results
@PIPELINES.register_module()
class TopDownHalfBodyTransform:
"""Data augmentation with half-body transform. Keep only the upper body or
the lower body at random.
Required keys: 'joints_3d', 'joints_3d_visible', and 'ann_info'.
Modifies key: 'scale' and 'center'.
Args:
num_joints_half_body (int): Threshold of performing
half-body transform. If the body has fewer number
of joints (< num_joints_half_body), ignore this step.
prob_half_body (float): Probability of half-body transform.
"""
def __init__(self, num_joints_half_body=8, prob_half_body=0.3):
self.num_joints_half_body = num_joints_half_body
self.prob_half_body = prob_half_body
@staticmethod
def half_body_transform(cfg, joints_3d, joints_3d_visible):
"""Get center&scale for half-body transform."""
upper_joints = []
lower_joints = []
for joint_id in range(cfg['num_joints']):
if joints_3d_visible[joint_id][0] > 0:
if joint_id in cfg['upper_body_ids']:
upper_joints.append(joints_3d[joint_id])
else:
lower_joints.append(joints_3d[joint_id])
if np.random.randn() < 0.5 and len(upper_joints) > 2:
selected_joints = upper_joints
elif len(lower_joints) > 2:
selected_joints = lower_joints
else:
selected_joints = upper_joints
if len(selected_joints) < 2:
return None, None
selected_joints = np.array(selected_joints, dtype=np.float32)
center = selected_joints.mean(axis=0)[:2]
left_top = np.amin(selected_joints, axis=0)
right_bottom = np.amax(selected_joints, axis=0)
w = right_bottom[0] - left_top[0]
h = right_bottom[1] - left_top[1]
aspect_ratio = cfg['image_size'][0] / cfg['image_size'][1]
if w > aspect_ratio * h:
h = w * 1.0 / aspect_ratio
elif w < aspect_ratio * h:
w = h * aspect_ratio
scale = np.array([w / 200.0, h / 200.0], dtype=np.float32)
scale = scale * 1.5
return center, scale
def __call__(self, results):
"""Perform data augmentation with half-body transform."""
joints_3d = results['joints_3d']
joints_3d_visible = results['joints_3d_visible']
if (np.sum(joints_3d_visible[:, 0]) > self.num_joints_half_body
and np.random.rand() < self.prob_half_body):
c_half_body, s_half_body = self.half_body_transform(
results['ann_info'], joints_3d, joints_3d_visible)
if c_half_body is not None and s_half_body is not None:
results['center'] = c_half_body
results['scale'] = s_half_body
return results
@PIPELINES.register_module()
class TopDownGetRandomScaleRotation:
"""Data augmentation with random scaling & rotating.
Required key: 'scale'.
Modifies key: 'scale' and 'rotation'.
Args:
rot_factor (int): Rotating to ``[-2*rot_factor, 2*rot_factor]``.
scale_factor (float): Scaling to ``[1-scale_factor, 1+scale_factor]``.
rot_prob (float): Probability of random rotation.
"""
def __init__(self, rot_factor=40, scale_factor=0.5, rot_prob=0.6):
self.rot_factor = rot_factor
self.scale_factor = scale_factor
self.rot_prob = rot_prob
def __call__(self, results):
"""Perform data augmentation with random scaling & rotating."""
s = results['scale']
sf = self.scale_factor
rf = self.rot_factor
s_factor = np.clip(np.random.randn() * sf + 1, 1 - sf, 1 + sf)
s = s * s_factor
r_factor = np.clip(np.random.randn() * rf, -rf * 2, rf * 2)
r = r_factor if np.random.rand() <= self.rot_prob else 0
results['scale'] = s
results['rotation'] = r
return results
@PIPELINES.register_module()
class TopDownAffine:
"""Affine transform the image to make input.
Required keys:'img', 'joints_3d', 'joints_3d_visible', 'ann_info','scale',
'rotation' and 'center'.
Modified keys:'img', 'joints_3d', and 'joints_3d_visible'.
Args:
use_udp (bool): To use unbiased data processing.
Paper ref: Huang et al. The Devil is in the Details: Delving into
Unbiased Data Processing for Human Pose Estimation (CVPR 2020).
"""
def __init__(self, use_udp=False):
self.use_udp = use_udp
def __call__(self, results):
image_size = results['ann_info']['image_size']
img = results['img']
joints_3d = results['joints_3d']
joints_3d_visible = results['joints_3d_visible']
c = results['center']
s = results['scale']
r = results['rotation']
if self.use_udp:
trans = get_warp_matrix(r, c * 2.0, image_size - 1.0, s * 200.0)
if not isinstance(img, list):
img = cv2.warpAffine(
img,
trans, (int(image_size[0]), int(image_size[1])),
flags=cv2.INTER_LINEAR)
else:
img = [
cv2.warpAffine(
i,
trans, (int(image_size[0]), int(image_size[1])),
flags=cv2.INTER_LINEAR) for i in img
]
joints_3d[:, 0:2] = \
warp_affine_joints(joints_3d[:, 0:2].copy(), trans)
else:
trans = get_affine_transform(c, s, r, image_size)
if not isinstance(img, list):
img = cv2.warpAffine(
img,
trans, (int(image_size[0]), int(image_size[1])),
flags=cv2.INTER_LINEAR)
else:
img = [
cv2.warpAffine(
i,
trans, (int(image_size[0]), int(image_size[1])),
flags=cv2.INTER_LINEAR) for i in img
]
for i in range(results['ann_info']['num_joints']):
if joints_3d_visible[i, 0] > 0.0:
joints_3d[i,
0:2] = affine_transform(joints_3d[i, 0:2], trans)
results['img'] = img
results['joints_3d'] = joints_3d
results['joints_3d_visible'] = joints_3d_visible
return results
@PIPELINES.register_module()
class TopDownGenerateTarget:
"""Generate the target heatmap.
Required keys: 'joints_3d', 'joints_3d_visible', 'ann_info'.
Modified keys: 'target', and 'target_weight'.
Args:
sigma: Sigma of heatmap gaussian for 'MSRA' approach.
kernel: Kernel of heatmap gaussian for 'Megvii' approach.
encoding (str): Approach to generate target heatmaps.
Currently supported approaches: 'MSRA', 'Megvii', 'UDP'.
Default:'MSRA'
unbiased_encoding (bool): Option to use unbiased
encoding methods.
Paper ref: Zhang et al. Distribution-Aware Coordinate
Representation for Human Pose Estimation (CVPR 2020).
keypoint_pose_distance: Keypoint pose distance for UDP.
Paper ref: Huang et al. The Devil is in the Details: Delving into
Unbiased Data Processing for Human Pose Estimation (CVPR 2020).
target_type (str): supported targets: 'GaussianHeatmap',
'CombinedTarget'. Default:'GaussianHeatmap'
CombinedTarget: The combination of classification target
(response map) and regression target (offset map).
Paper ref: Huang et al. The Devil is in the Details: Delving into
Unbiased Data Processing for Human Pose Estimation (CVPR 2020).
"""
def __init__(self,
sigma=2,
kernel=(11, 11),
valid_radius_factor=0.0546875,
target_type='GaussianHeatmap',
encoding='MSRA',
unbiased_encoding=False):
self.sigma = sigma
self.unbiased_encoding = unbiased_encoding
self.kernel = kernel
self.valid_radius_factor = valid_radius_factor
self.target_type = target_type
self.encoding = encoding
def _msra_generate_target(self, cfg, joints_3d, joints_3d_visible, sigma):
"""Generate the target heatmap via "MSRA" approach.
Args:
cfg (dict): data config
joints_3d: np.ndarray ([num_joints, 3])
joints_3d_visible: np.ndarray ([num_joints, 3])
sigma: Sigma of heatmap gaussian
Returns:
tuple: A tuple containing targets.
- target: Target heatmaps.
- target_weight: (1: visible, 0: invisible)
"""
num_joints = cfg['num_joints']
image_size = cfg['image_size']
W, H = cfg['heatmap_size']
joint_weights = cfg['joint_weights']
use_different_joint_weights = cfg['use_different_joint_weights']
target_weight = np.zeros((num_joints, 1), dtype=np.float32)
target = np.zeros((num_joints, H, W), dtype=np.float32)
# 3-sigma rule
tmp_size = sigma * 3
if self.unbiased_encoding:
for joint_id in range(num_joints):
target_weight[joint_id] = joints_3d_visible[joint_id, 0]
feat_stride = image_size / [W, H]
mu_x = joints_3d[joint_id][0] / feat_stride[0]
mu_y = joints_3d[joint_id][1] / feat_stride[1]
# Check that any part of the gaussian is in-bounds
ul = [mu_x - tmp_size, mu_y - tmp_size]
br = [mu_x + tmp_size + 1, mu_y + tmp_size + 1]
if ul[0] >= W or ul[1] >= H or br[0] < 0 or br[1] < 0:
target_weight[joint_id] = 0
if target_weight[joint_id] == 0:
continue
x = np.arange(0, W, 1, np.float32)
y = np.arange(0, H, 1, np.float32)
y = y[:, None]
if target_weight[joint_id] > 0.5:
target[joint_id] = np.exp(-((x - mu_x)**2 +
(y - mu_y)**2) /
(2 * sigma**2))
else:
for joint_id in range(num_joints):
target_weight[joint_id] = joints_3d_visible[joint_id, 0]
feat_stride = image_size / [W, H]
mu_x = int(joints_3d[joint_id][0] / feat_stride[0] + 0.5)
mu_y = int(joints_3d[joint_id][1] / feat_stride[1] + 0.5)
# Check that any part of the gaussian is in-bounds
ul = [int(mu_x - tmp_size), int(mu_y - tmp_size)]
br = [int(mu_x + tmp_size + 1), int(mu_y + tmp_size + 1)]
if ul[0] >= W or ul[1] >= H or br[0] < 0 or br[1] < 0:
target_weight[joint_id] = 0
if target_weight[joint_id] > 0.5:
size = 2 * tmp_size + 1
x = np.arange(0, size, 1, np.float32)
y = x[:, None]
x0 = y0 = size // 2
# The gaussian is not normalized,
# we want the center value to equal 1
g = np.exp(-((x - x0)**2 + (y - y0)**2) / (2 * sigma**2))
# Usable gaussian range
g_x = max(0, -ul[0]), min(br[0], W) - ul[0]
g_y = max(0, -ul[1]), min(br[1], H) - ul[1]
# Image range
img_x = max(0, ul[0]), min(br[0], W)
img_y = max(0, ul[1]), min(br[1], H)
target[joint_id][img_y[0]:img_y[1], img_x[0]:img_x[1]] = \
g[g_y[0]:g_y[1], g_x[0]:g_x[1]]
if use_different_joint_weights:
target_weight = np.multiply(target_weight, joint_weights)
return target, target_weight
def _megvii_generate_target(self, cfg, joints_3d, joints_3d_visible,
kernel):
"""Generate the target heatmap via "Megvii" approach.
Args:
cfg (dict): data config
joints_3d: np.ndarray ([num_joints, 3])
joints_3d_visible: np.ndarray ([num_joints, 3])
kernel: Kernel of heatmap gaussian
Returns:
tuple: A tuple containing targets.
- target: Target heatmaps.
- target_weight: (1: visible, 0: invisible)
"""
num_joints = cfg['num_joints']
image_size = cfg['image_size']
W, H = cfg['heatmap_size']
heatmaps = np.zeros((num_joints, H, W), dtype='float32')
target_weight = np.zeros((num_joints, 1), dtype=np.float32)
for i in range(num_joints):
target_weight[i] = joints_3d_visible[i, 0]
if target_weight[i] < 1:
continue
target_y = int(joints_3d[i, 1] * H / image_size[1])
target_x = int(joints_3d[i, 0] * W / image_size[0])
if (target_x >= W or target_x < 0) \
or (target_y >= H or target_y < 0):
target_weight[i] = 0
continue
heatmaps[i, target_y, target_x] = 1
heatmaps[i] = cv2.GaussianBlur(heatmaps[i], kernel, 0)
maxi = heatmaps[i, target_y, target_x]
heatmaps[i] /= maxi / 255
return heatmaps, target_weight
def _udp_generate_target(self, cfg, joints_3d, joints_3d_visible, factor,
target_type):
"""Generate the target heatmap via 'UDP' approach. Paper ref: Huang et
al. The Devil is in the Details: Delving into Unbiased Data Processing
for Human Pose Estimation (CVPR 2020).
Note:
- num keypoints: K
- heatmap height: H
- heatmap width: W
- num target channels: C
- C = K if target_type=='GaussianHeatmap'
- C = 3*K if target_type=='CombinedTarget'
Args:
cfg (dict): data config
joints_3d (np.ndarray[K, 3]): Annotated keypoints.
joints_3d_visible (np.ndarray[K, 3]): Visibility of keypoints.
factor (float): kernel factor for GaussianHeatmap target or
valid radius factor for CombinedTarget.
target_type (str): 'GaussianHeatmap' or 'CombinedTarget'.
GaussianHeatmap: Heatmap target with gaussian distribution.
CombinedTarget: The combination of classification target
(response map) and regression target (offset map).
Returns:
tuple: A tuple containing targets.
- target (np.ndarray[C, H, W]): Target heatmaps.
- target_weight (np.ndarray[K, 1]): (1: visible, 0: invisible)
"""
num_joints = cfg['num_joints']
image_size = cfg['image_size']
heatmap_size = cfg['heatmap_size']
joint_weights = cfg['joint_weights']
use_different_joint_weights = cfg['use_different_joint_weights']
target_weight = np.ones((num_joints, 1), dtype=np.float32)
target_weight[:, 0] = joints_3d_visible[:, 0]
if target_type.lower() == 'GaussianHeatmap'.lower():
target = np.zeros((num_joints, heatmap_size[1], heatmap_size[0]),
dtype=np.float32)
tmp_size = factor * 3
# prepare for gaussian
size = 2 * tmp_size + 1
x = np.arange(0, size, 1, np.float32)
y = x[:, None]
for joint_id in range(num_joints):
feat_stride = (image_size - 1.0) / (heatmap_size - 1.0)
mu_x = int(joints_3d[joint_id][0] / feat_stride[0] + 0.5)
mu_y = int(joints_3d[joint_id][1] / feat_stride[1] + 0.5)
# Check that any part of the gaussian is in-bounds
ul = [int(mu_x - tmp_size), int(mu_y - tmp_size)]
br = [int(mu_x + tmp_size + 1), int(mu_y + tmp_size + 1)]
if ul[0] >= heatmap_size[0] or ul[1] >= heatmap_size[1] \
or br[0] < 0 or br[1] < 0:
# If not, just return the image as is
target_weight[joint_id] = 0
continue
# # Generate gaussian
mu_x_ac = joints_3d[joint_id][0] / feat_stride[0]
mu_y_ac = joints_3d[joint_id][1] / feat_stride[1]
x0 = y0 = size // 2
x0 += mu_x_ac - mu_x
y0 += mu_y_ac - mu_y
g = np.exp(-((x - x0)**2 + (y - y0)**2) / (2 * factor**2))
# Usable gaussian range
g_x = max(0, -ul[0]), min(br[0], heatmap_size[0]) - ul[0]
g_y = max(0, -ul[1]), min(br[1], heatmap_size[1]) - ul[1]
# Image range
img_x = max(0, ul[0]), min(br[0], heatmap_size[0])
img_y = max(0, ul[1]), min(br[1], heatmap_size[1])
v = target_weight[joint_id]
if v > 0.5:
target[joint_id][img_y[0]:img_y[1], img_x[0]:img_x[1]] = \
g[g_y[0]:g_y[1], g_x[0]:g_x[1]]
elif target_type.lower() == 'CombinedTarget'.lower():
target = np.zeros(
(num_joints, 3, heatmap_size[1] * heatmap_size[0]),
dtype=np.float32)
feat_width = heatmap_size[0]
feat_height = heatmap_size[1]
feat_x_int = np.arange(0, feat_width)
feat_y_int = np.arange(0, feat_height)
feat_x_int, feat_y_int = np.meshgrid(feat_x_int, feat_y_int)
feat_x_int = feat_x_int.flatten()
feat_y_int = feat_y_int.flatten()
# Calculate the radius of the positive area in classification
# heatmap.
valid_radius = factor * heatmap_size[1]
feat_stride = (image_size - 1.0) / (heatmap_size - 1.0)
for joint_id in range(num_joints):
mu_x = joints_3d[joint_id][0] / feat_stride[0]
mu_y = joints_3d[joint_id][1] / feat_stride[1]
x_offset = (mu_x - feat_x_int) / valid_radius
y_offset = (mu_y - feat_y_int) / valid_radius
dis = x_offset**2 + y_offset**2
keep_pos = np.where(dis <= 1)[0]
v = target_weight[joint_id]
if v > 0.5:
target[joint_id, 0, keep_pos] = 1
target[joint_id, 1, keep_pos] = x_offset[keep_pos]
target[joint_id, 2, keep_pos] = y_offset[keep_pos]
target = target.reshape(num_joints * 3, heatmap_size[1],
heatmap_size[0])
else:
raise ValueError('target_type should be either '
"'GaussianHeatmap' or 'CombinedTarget'")
if use_different_joint_weights:
target_weight = np.multiply(target_weight, joint_weights)
return target, target_weight
def __call__(self, results):
"""Generate the target heatmap."""
joints_3d = results['joints_3d']
joints_3d_visible = results['joints_3d_visible']
assert self.encoding in ['MSRA', 'Megvii', 'UDP']
if self.encoding == 'MSRA':
if isinstance(self.sigma, list):
num_sigmas = len(self.sigma)
cfg = results['ann_info']
num_joints = cfg['num_joints']
heatmap_size = cfg['heatmap_size']
target = np.empty(
(0, num_joints, heatmap_size[1], heatmap_size[0]),
dtype=np.float32)
target_weight = np.empty((0, num_joints, 1), dtype=np.float32)
for i in range(num_sigmas):
target_i, target_weight_i = self._msra_generate_target(
cfg, joints_3d, joints_3d_visible, self.sigma[i])
target = np.concatenate([target, target_i[None]], axis=0)
target_weight = np.concatenate(
[target_weight, target_weight_i[None]], axis=0)
else:
target, target_weight = self._msra_generate_target(
results['ann_info'], joints_3d, joints_3d_visible,
self.sigma)
elif self.encoding == 'Megvii':
if isinstance(self.kernel, list):
num_kernels = len(self.kernel)
cfg = results['ann_info']
num_joints = cfg['num_joints']
W, H = cfg['heatmap_size']
target = np.empty((0, num_joints, H, W), dtype=np.float32)
target_weight = np.empty((0, num_joints, 1), dtype=np.float32)
for i in range(num_kernels):
target_i, target_weight_i = self._megvii_generate_target(
cfg, joints_3d, joints_3d_visible, self.kernel[i])
target = np.concatenate([target, target_i[None]], axis=0)
target_weight = np.concatenate(
[target_weight, target_weight_i[None]], axis=0)
else:
target, target_weight = self._megvii_generate_target(
results['ann_info'], joints_3d, joints_3d_visible,
self.kernel)
elif self.encoding == 'UDP':
if self.target_type.lower() == 'CombinedTarget'.lower():
factors = self.valid_radius_factor
channel_factor = 3
elif self.target_type.lower() == 'GaussianHeatmap'.lower():
factors = self.sigma
channel_factor = 1
else:
raise ValueError('target_type should be either '
"'GaussianHeatmap' or 'CombinedTarget'")
if isinstance(factors, list):
num_factors = len(factors)
cfg = results['ann_info']
num_joints = cfg['num_joints']
W, H = cfg['heatmap_size']
target = np.empty((0, channel_factor * num_joints, H, W),
dtype=np.float32)
target_weight = np.empty((0, num_joints, 1), dtype=np.float32)
for i in range(num_factors):
target_i, target_weight_i = self._udp_generate_target(
cfg, joints_3d, joints_3d_visible, factors[i],
self.target_type)
target = np.concatenate([target, target_i[None]], axis=0)
target_weight = np.concatenate(
[target_weight, target_weight_i[None]], axis=0)
else:
target, target_weight = self._udp_generate_target(
results['ann_info'], joints_3d, joints_3d_visible, factors,
self.target_type)
else:
raise ValueError(
f'Encoding approach {self.encoding} is not supported!')
if results['ann_info'].get('max_num_joints', None) is not None:
W, H = results['ann_info']['heatmap_size']
padded_length = int(results['ann_info'].get('max_num_joints') - results['ann_info'].get('num_joints'))
target_weight = np.concatenate([target_weight, np.zeros((padded_length, 1), dtype=np.float32)], 0)
target = np.concatenate([target, np.zeros((padded_length, H, W), dtype=np.float32)], 0)
results['target'] = target
results['target_weight'] = target_weight
results['dataset_idx'] = results['ann_info'].get('dataset_idx', 0)
return results
@PIPELINES.register_module()
class TopDownGenerateTargetRegression:
"""Generate the target regression vector (coordinates).
Required keys: 'joints_3d', 'joints_3d_visible', 'ann_info'. Modified keys:
'target', and 'target_weight'.
"""
def __init__(self):
pass
def _generate_target(self, cfg, joints_3d, joints_3d_visible):
"""Generate the target regression vector.
Args:
cfg (dict): data config
joints_3d: np.ndarray([num_joints, 3])
joints_3d_visible: np.ndarray([num_joints, 3])
Returns:
target, target_weight(1: visible, 0: invisible)
"""
image_size = cfg['image_size']
joint_weights = cfg['joint_weights']
use_different_joint_weights = cfg['use_different_joint_weights']
mask = (joints_3d[:, 0] >= 0) * (
joints_3d[:, 0] <= image_size[0] - 1) * (joints_3d[:, 1] >= 0) * (
joints_3d[:, 1] <= image_size[1] - 1)
target = joints_3d[:, :2] / image_size
target = target.astype(np.float32)
target_weight = joints_3d_visible[:, :2] * mask[:, None]
if use_different_joint_weights:
target_weight = np.multiply(target_weight, joint_weights)
return target, target_weight
def __call__(self, results):
"""Generate the target heatmap."""
joints_3d = results['joints_3d']
joints_3d_visible = results['joints_3d_visible']
target, target_weight = self._generate_target(results['ann_info'],
joints_3d,
joints_3d_visible)
results['target'] = target
results['target_weight'] = target_weight
return results
@PIPELINES.register_module()
class TopDownRandomTranslation:
"""Data augmentation with random translation.
Required key: 'scale' and 'center'.
Modifies key: 'center'.
Note:
- bbox height: H
- bbox width: W
Args:
trans_factor (float): Translating center to
``[-trans_factor, trans_factor] * [W, H] + center``.
trans_prob (float): Probability of random translation.
"""
def __init__(self, trans_factor=0.15, trans_prob=1.0):
self.trans_factor = trans_factor
self.trans_prob = trans_prob
def __call__(self, results):
"""Perform data augmentation with random translation."""
center = results['center']
scale = results['scale']
if np.random.rand() <= self.trans_prob:
# reference bbox size is [200, 200] pixels
center += self.trans_factor * np.random.uniform(
-1, 1, size=2) * scale * 200
results['center'] = center
return results