#!/usr/bin/env python
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# Copyright 2024 Brainchip Holdings Ltd.
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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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"""
Utils for Centernet.
"""
__all__ = ['build_centernet_aug_pipeline', 'create_centernet_targets']
import tensorflow as tf
from imgaug import augmenters as iaa
from ..detection.data_utils import Coord
from ..detection.box_utils import compute_center_wh, compute_center_xy
def _gaussian2D(radius, sigma=1, eps=tf.keras.backend.epsilon()):
"""Generate 2D gaussian kernel.
Args:
radius (int): Radius of gaussian kernel.
sigma (int, optional): Sigma of gaussian function. Defaults to 1.
eps (float, optional): Epsilon value. Defaults to 1e-7.
Returns:
tf.Tensor: Gaussian kernel with a `(2 * radius + 1) x (2 * radius + 1)` shape.
"""
x = tf.reshape(tf.range(-radius, radius + 1, dtype=tf.float32), [1, -1])
y = tf.reshape(tf.range(-radius, radius + 1, dtype=tf.float32), [-1, 1])
h = tf.exp(-(x * x + y * y) / tf.cast((2 * sigma * sigma), dtype=tf.float32))
# Clamp smaller values to zero
h = tf.where(h < (eps * tf.reduce_max(h)), 0.0, h)
return h
def _gen_gaussian_target(heatmap, center, obj_idx, radius):
"""Generate 2D gaussian heatmap.
Args:
heatmap (tf.Tensor): Input heatmap, the gaussian kernel will cover on it and maintain
the max value.
center (list[int]): Coordinates of gaussian kernel's center.
obj_idx (int): The class index for the center point.
radius (int): Radius of gaussian kernel.
Returns:
out_heatmap (tf.Tensor): Updated heatmap covered by gaussian kernel.
Note:
Taken from pytorch
"""
diameter = 2 * radius + 1
gaussian_kernel = _gaussian2D(radius, sigma=diameter / 6)
x, y = center
height = tf.shape(heatmap)[0]
width = tf.shape(heatmap)[1]
# Find the smallest value so that if the point is near the edge we don't end outside
# (e.g. x = 3 and radius is 10, then we go from the x-3 to x+10)
left = tf.minimum(x, radius)
right = tf.minimum(width - x, radius + 1)
top = tf.minimum(y, radius)
bottom = tf.minimum(height - y, radius + 1)
# Compare the gaussian kernel to the heatmap (in case there's already a point of
# interest there) and keep the max value
flattened_kernel = tf.reshape(gaussian_kernel, [-1])
# Range the dimensions
# Generate the grid of indices
d0_range = tf.range(y - top, y + bottom)
d1_range = tf.range(x - left, x + right)
d1_grid, d0_grid = tf.meshgrid(d1_range, d0_range)
# Flatten the grid of indices
indices = tf.reshape(
tf.stack([d1_grid, d0_grid, tf.fill(tf.shape(d0_grid), obj_idx)], axis=-1), (-1, 3))
# Update heatmap
heatmap = tf.tensor_scatter_nd_update(heatmap, indices, flattened_kernel)
return heatmap
def _gaussian_radius(det_size, min_overlap):
r"""Generate 2D gaussian radius.
This function is modified from the `official github repo
<https://github.com/princeton-vl/CornerNet-Lite/blob/master/core/sample/
utils.py#L65>`_.
Given ``min_overlap``, radius could computed by a quadratic equation
according to Vieta's formulas.
There are 3 cases for computing gaussian radius, details are following:
- Case 1: one corner is inside the gt box and the other is outside.
.. code:: text
|< width >|
lt-+----------+ -
| | | ^
+--x----------+--+
| | | |
| | | | height
| | overlap | |
| | | |
| | | | v
+--+---------br--+ -
| | |
+----------+--x
To ensure IoU of generated box and gt box is larger than ``min_overlap``:
.. math::
\cfrac{(w-r)*(h-r)}{w*h+(w+h)r-r^2} \ge {iou} \quad\Rightarrow\quad
{r^2-(w+h)r+\cfrac{1-iou}{1+iou}*w*h} \ge 0 \\
{a} = 1,\quad{b} = {-(w+h)},\quad{c} = {\cfrac{1-iou}{1+iou}*w*h}
{r} \le \cfrac{-b-\sqrt{b^2-4*a*c}}{2*a}
- Case 2: both two corners are inside the gt box.
.. code:: text
|< width >|
lt-+----------+ -
| | | ^
+--x-------+ |
| | | |
| |overlap| | height
| | | |
| +-------x--+
| | | v
+----------+-br -
To ensure IoU of generated box and gt box is larger than ``min_overlap``:
.. math::
\cfrac{(w-2*r)*(h-2*r)}{w*h} \ge {iou} \quad\Rightarrow\quad
{4r^2-2(w+h)r+(1-iou)*w*h} \ge 0 \\
{a} = 4,\quad {b} = {-2(w+h)},\quad {c} = {(1-iou)*w*h}
{r} \le \cfrac{-b-\sqrt{b^2-4*a*c}}{2*a}
- Case 3: both two corners are outside the gt box.
.. code:: text
|< width >|
x--+----------------+
| | |
+-lt-------------+ | -
| | | | ^
| | | |
| | overlap | | height
| | | |
| | | | v
| +------------br--+ -
| | |
+----------------+--x
To ensure IoU of generated box and gt box is larger than ``min_overlap``:
.. math::
\cfrac{w*h}{(w+2*r)*(h+2*r)} \ge {iou} \quad\Rightarrow\quad
{4*iou*r^2+2*iou*(w+h)r+(iou-1)*w*h} \le 0 \\
{a} = {4*iou},\quad {b} = {2*iou*(w+h)},\quad {c} = {(iou-1)*w*h} \\
{r} \le \cfrac{-b+\sqrt{b^2-4*a*c}}{2*a}
Args:
det_size (list[int]): Shape of object.
min_overlap (float): Min IoU with ground truth for boxes generated by
keypoints inside the gaussian kernel.
Returns:
radius (tf.Tensor): Radius of gaussian kernel.
Notes:
Explanation of figure: ``lt`` and ``br`` indicates the left-top and bottom-right
corner of ground truth box. ``x`` indicates the generated corner at the limited
position when ``radius=r``.
"""
height, width = det_size
a1 = 1
b1 = (height + width)
c1 = width * height * (1 - min_overlap) / (1 + min_overlap)
sq1 = tf.sqrt(b1**2 - 4 * a1 * c1)
r1 = (b1 - sq1) / (2 * a1)
a2 = 4
b2 = 2 * (height + width)
c2 = (1 - min_overlap) * width * height
sq2 = tf.sqrt(b2**2 - 4 * a2 * c2)
r2 = (b2 - sq2) / (2 * a2)
a3 = 4 * min_overlap
b3 = -2 * min_overlap * (height + width)
c3 = (min_overlap - 1) * width * height
sq3 = tf.sqrt(b3**2 - 4 * a3 * c3)
r3 = (b3 + sq3) / (2 * a3)
return tf.reduce_min([r1, r2, r3])
[docs]def build_centernet_aug_pipeline():
""" Defines a sequence of augmentation steps for Centernet training
that will be applied to every image.
Returns:
iaa.Sequential: sequence of augmentation.
"""
# augmentors by https://github.com/aleju/imgaug
def sometimes(aug): return iaa.Sometimes(0.5, aug)
# All augmenters with per_channel=0.5 will sample one value per
# image in 50% of all cases. In all other cases they will sample new
# values per channel.
return iaa.Sequential(
[
# apply the following augmenters to most images
sometimes(iaa.Affine(rotate=0)),
# execute 0 to 5 of the following (less important) augmenters
# per image. Don't execute all of them, as that would often be
# way too strong
iaa.SomeOf(
(0, 5),
[
iaa.OneOf([
# blur images with a sigma between 0 and 3.0
iaa.GaussianBlur((0, 3.0)),
# blur image using local means (kernel sizes between 2 and 7)
iaa.AverageBlur(k=(2, 7)),
# blur image using local medians (kernel sizes between 3 and 11)
iaa.MedianBlur(k=(3, 11)),
]),
# sharpen images
iaa.Sharpen(alpha=(0, 1.0), lightness=(0.75, 1.5)),
iaa.LinearContrast((0.5, 2.0), per_channel=0.5),
iaa.AdditiveGaussianNoise(loc=0, scale=(0.0, 0.05 * 255), per_channel=0.5),
# randomly remove up to 10% of the pixels
iaa.OneOf([iaa.Dropout((0.01, 0.1), per_channel=0.5),
iaa.CoarseDropout((0.01, 0.05), size_percent=0.5)]),
# change brightness of images
iaa.Add((-10, 10), per_channel=0.5),
iaa.Multiply((0.5, 1.5), per_channel=0.5),
iaa.OneOf([
iaa.pillike.Equalize(),
iaa.pillike.Autocontrast()
])
], random_order=True)
],
random_order=True)
[docs]def create_centernet_targets(objects,
grid_size,
num_classes):
"""
Creates Centernet-style targets tensor for the given objects.
Args:
objects (dict): Dictionary containing information about objects in the image,
including labels and bounding boxes.
grid_size (tuple): The grid size used for Centernet target generation.
num_classes (int): The number of classes.
Returns:
targets (tf.Tensor): The targets output tensor.
"""
targets = tf.zeros((grid_size[0], grid_size[1], 2 + 2 + num_classes), dtype=tf.float32)
num_objects = tf.shape(objects['label'])[0]
for idx in range(num_objects):
bbox = objects['bbox'][idx]
if bbox[Coord.x2] > bbox[Coord.x1] and bbox[Coord.y2] > bbox[Coord.y1]:
center_x, center_y = compute_center_xy(bbox, grid_size)
# find grid index where the center is located
grid_x = tf.cast(center_x, tf.int32)
grid_y = tf.cast(center_y, tf.int32)
if grid_x < grid_size[1] and grid_y < grid_size[0]:
obj_indx = objects['label'][idx]
center_w, center_h = compute_center_wh(bbox, grid_size)
# get the center point and use a gaussian kernel as the target
radius = _gaussian_radius([center_h, center_w], min_overlap=0.3)
# check that the radius is positive
radius = tf.maximum(tf.cast(radius, dtype=tf.int32), 0)
heatmap = tf.zeros(
(grid_size[0], grid_size[1], num_classes)
)
heatmap = _gen_gaussian_target(heatmap, [grid_y, grid_x], obj_indx, radius)
# update targets heatmap
indices = [[i, j, k] for i in range(grid_size[0]) for j in range(
grid_size[1]) for k in range(num_classes)]
updates = tf.gather_nd(params=heatmap, indices=indices)
targets = tf.tensor_scatter_nd_add(targets, indices, updates)
# update targets width
targets = tf.tensor_scatter_nd_update(
targets, [[grid_y, grid_x, num_classes]], [center_w])
# update targets height
targets = tf.tensor_scatter_nd_update(
targets, [[grid_y, grid_x, num_classes + 1]], [center_h])
# update targets center x
targets = tf.tensor_scatter_nd_update(
targets,
[[grid_y, grid_x, num_classes + 2]],
[center_x - tf.cast(grid_x, dtype=tf.float32)])
# update targets center y
targets = tf.tensor_scatter_nd_update(
targets,
[[grid_y, grid_x, num_classes + 3]],
[center_y - tf.cast(grid_y, dtype=tf.float32)])
return targets