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import numpy as np
from PIL import Image
def nms(boxes, overlap_threshold=0.5, mode='union'):
"""Non-maximum suppression.
Arguments:
boxes: a float numpy array of shape [n, 5],
where each row is (xmin, ymin, xmax, ymax, score).
overlap_threshold: a float number.
mode: 'union' or 'min'.
Returns:
list with indices of the selected boxes
"""
# if there are no boxes, return the empty list
if len(boxes) == 0:
return []
# list of picked indices
pick = []
# grab the coordinates of the bounding boxes
x1, y1, x2, y2, score = [boxes[:, i] for i in range(5)]
area = (x2 - x1 + 1.0)*(y2 - y1 + 1.0)
ids = np.argsort(score) # in increasing order
while len(ids) > 0:
# grab index of the largest value
last = len(ids) - 1
i = ids[last]
pick.append(i)
# compute intersections
# of the box with the largest score
# with the rest of boxes
# left top corner of intersection boxes
ix1 = np.maximum(x1[i], x1[ids[:last]])
iy1 = np.maximum(y1[i], y1[ids[:last]])
# right bottom corner of intersection boxes
ix2 = np.minimum(x2[i], x2[ids[:last]])
iy2 = np.minimum(y2[i], y2[ids[:last]])
# width and height of intersection boxes
w = np.maximum(0.0, ix2 - ix1 + 1.0)
h = np.maximum(0.0, iy2 - iy1 + 1.0)
# intersections' areas
inter = w * h
if mode == 'min':
overlap = inter/np.minimum(area[i], area[ids[:last]])
elif mode == 'union':
# intersection over union (IoU)
overlap = inter/(area[i] + area[ids[:last]] - inter)
# delete all boxes where overlap is too big
ids = np.delete(
ids,
np.concatenate([[last], np.where(overlap > overlap_threshold)[0]])
)
return pick
def convert_to_square(bboxes):
"""Convert bounding boxes to a square form.
Arguments:
bboxes: a float numpy array of shape [n, 5].
Returns:
a float numpy array of shape [n, 5],
squared bounding boxes.
"""
square_bboxes = np.zeros_like(bboxes)
x1, y1, x2, y2 = [bboxes[:, i] for i in range(4)]
h = y2 - y1 + 1.0
w = x2 - x1 + 1.0
max_side = np.maximum(h, w)
square_bboxes[:, 0] = x1 + w*0.5 - max_side*0.5
square_bboxes[:, 1] = y1 + h*0.5 - max_side*0.5
square_bboxes[:, 2] = square_bboxes[:, 0] + max_side - 1.0
square_bboxes[:, 3] = square_bboxes[:, 1] + max_side - 1.0
return square_bboxes
def calibrate_box(bboxes, offsets):
"""Transform bounding boxes to be more like true bounding boxes.
'offsets' is one of the outputs of the nets.
Arguments:
bboxes: a float numpy array of shape [n, 5].
offsets: a float numpy array of shape [n, 4].
Returns:
a float numpy array of shape [n, 5].
"""
x1, y1, x2, y2 = [bboxes[:, i] for i in range(4)]
w = x2 - x1 + 1.0
h = y2 - y1 + 1.0
w = np.expand_dims(w, 1)
h = np.expand_dims(h, 1)
# this is what happening here:
# tx1, ty1, tx2, ty2 = [offsets[:, i] for i in range(4)]
# x1_true = x1 + tx1*w
# y1_true = y1 + ty1*h
# x2_true = x2 + tx2*w
# y2_true = y2 + ty2*h
# below is just more compact form of this
# are offsets always such that
# x1 < x2 and y1 < y2 ?
translation = np.hstack([w, h, w, h])*offsets
bboxes[:, 0:4] = bboxes[:, 0:4] + translation
return bboxes
def get_image_boxes(bounding_boxes, img, size=24):
"""Cut out boxes from the image.
Arguments:
bounding_boxes: a float numpy array of shape [n, 5].
img: an instance of PIL.Image.
size: an integer, size of cutouts.
Returns:
a float numpy array of shape [n, 3, size, size].
"""
num_boxes = len(bounding_boxes)
width, height = img.size
[dy, edy, dx, edx, y, ey, x, ex, w, h] = correct_bboxes(bounding_boxes, width, height)
img_boxes = np.zeros((num_boxes, 3, size, size), 'float32')
for i in range(num_boxes):
img_box = np.zeros((h[i], w[i], 3), 'uint8')
img_array = np.asarray(img, 'uint8')
img_box[dy[i]:(edy[i] + 1), dx[i]:(edx[i] + 1), :] =\
img_array[y[i]:(ey[i] + 1), x[i]:(ex[i] + 1), :]
# resize
img_box = Image.fromarray(img_box)
img_box = img_box.resize((size, size), Image.BILINEAR)
img_box = np.asarray(img_box, 'float32')
img_boxes[i, :, :, :] = _preprocess(img_box)
return img_boxes
def correct_bboxes(bboxes, width, height):
"""Crop boxes that are too big and get coordinates
with respect to cutouts.
Arguments:
bboxes: a float numpy array of shape [n, 5],
where each row is (xmin, ymin, xmax, ymax, score).
width: a float number.
height: a float number.
Returns:
dy, dx, edy, edx: a int numpy arrays of shape [n],
coordinates of the boxes with respect to the cutouts.
y, x, ey, ex: a int numpy arrays of shape [n],
corrected ymin, xmin, ymax, xmax.
h, w: a int numpy arrays of shape [n],
just heights and widths of boxes.
in the following order:
[dy, edy, dx, edx, y, ey, x, ex, w, h].
"""
x1, y1, x2, y2 = [bboxes[:, i] for i in range(4)]
w, h = x2 - x1 + 1.0, y2 - y1 + 1.0
num_boxes = bboxes.shape[0]
# 'e' stands for end
# (x, y) -> (ex, ey)
x, y, ex, ey = x1, y1, x2, y2
# we need to cut out a box from the image.
# (x, y, ex, ey) are corrected coordinates of the box
# in the image.
# (dx, dy, edx, edy) are coordinates of the box in the cutout
# from the image.
dx, dy = np.zeros((num_boxes,)), np.zeros((num_boxes,))
edx, edy = w.copy() - 1.0, h.copy() - 1.0
# if box's bottom right corner is too far right
ind = np.where(ex > width - 1.0)[0]
edx[ind] = w[ind] + width - 2.0 - ex[ind]
ex[ind] = width - 1.0
# if box's bottom right corner is too low
ind = np.where(ey > height - 1.0)[0]
edy[ind] = h[ind] + height - 2.0 - ey[ind]
ey[ind] = height - 1.0
# if box's top left corner is too far left
ind = np.where(x < 0.0)[0]
dx[ind] = 0.0 - x[ind]
x[ind] = 0.0
# if box's top left corner is too high
ind = np.where(y < 0.0)[0]
dy[ind] = 0.0 - y[ind]
y[ind] = 0.0
return_list = [dy, edy, dx, edx, y, ey, x, ex, w, h]
return_list = [i.astype('int32') for i in return_list]
return return_list
def _preprocess(img):
"""Preprocessing step before feeding the network.
Arguments:
img: a float numpy array of shape [h, w, c].
Returns:
a float numpy array of shape [1, c, h, w].
"""
img = img.transpose((2, 0, 1))
img = np.expand_dims(img, 0)
img = (img - 127.5)*0.0078125
return img
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