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1. The concept of target detection
Object detection is a popular direction in computer vision and digital image processing. It is widely used in robot navigation, intelligent video surveillance, industrial inspection, aerospace and many other fields. It has important practical significance to reduce the consumption of human capital through computer vision. Therefore, target detection has become a research hotspot in theory and application in recent years. It is an important branch of image processing and computer vision, and it is also the core part of intelligent monitoring systems. At the same time, target detection is also a basic in the field of pan-identification Algorithms play a vital role in subsequent tasks such as face recognition, gait recognition, crowd counting, and instance segmentation.
The task of object detection is to find out all the objects of interest in the image and determine their positions and categories. Due to the different shapes and postures of various objects, and the interference of factors such as illumination and occlusion during imaging, object detection has always been is one of the most serious challenges in the field of computer vision
2. Target detection algorithm evaluation index
Target detection needs to predict the specific position of the target and the target category. To determine whether a target is detected correctly, first determine whether the confidence of the predicted category reaches the threshold, and then determine whether the coincidence degree between the predicted frame and the actual frame exceeds the specified threshold. For the coincidence degree The definition of IoU is usually represented by IoU. IoU refers to the ratio of the intersection area between the target prediction frame and the actual frame to the union area between the two frames. The larger the IoU, the higher the overlap between the predicted frame and the actual frame. Higher detection is more accurate
The accuracy rate is the proportion of the predicted correct frame to all the predicted frames for a certain prediction category, and the recall rate is the proportion of the predicted correct frame to all the real frames for a certain prediction category. The two index calculation methods as follows
where TP represents the number of correctly predicted positive samples, FP represents the number of incorrectly predicted positive samples, and FN represents the number of incorrectly predicted negative true samples.
AP stands for average precision. Simply put, it is to average the Precision value on the PR curve. For the PR curve, we use integral to calculate
In practical applications, we do not directly calculate the PR curve, but smooth the PR curve, that is, for each point on the PR curve, the value of Precision takes the value of the largest Precision on the right side of the point
The performance comparison of the deep convolutional neural network target detection algorithm is as follows
| detection framework |
mAP |
FPS |
| R-FCN |
79.4 |
7 |
| Faster R-CNN |
76.4 |
5 |
| SSD500 |
76.8 |
19 |
| YOLO |
63.4 |
45 |
| YOLO v2 |
78.6 |
40 |
| YOLO v3 |
82.3 |
39 |
3. Target detection project actual combat
The training set used is the VOC data set, and the effect is shown as follows
The numbers represent the relative coordinates of the detected object in the picture
Classified as follows
4. Code
The project structure is as follows
The keras_frcnn folder contains various classes and methods used to implement Faster R-CNN
The test code is placed in the testing folder below
Part of the code is as follows. All codes are required. Please like and follow the collection and then private message in the comment area
from keras.layers import Layer
import keras.backend as K
if K.backend() == 'tensorflow':
import tensorflow as tf
class RoiPoolingConv(Layer):
'''ROI pooling layer for 2D inputs.
See Spatial Pyramid Pooling in Deep Convolutional Networks for Visual Recognition,
K. He, X. Zhang, S. Ren, J. Sun
# Arguments
pool_size: int
Size of pooling region to use. pool_size = 7 will result in a 7x7 region.
num_rois: number of regions of interest to be used
# Input shape
list of two 4D tensors [X_img,X_roi] with shape:
X_img:
`(1, channels, rows, cols)` if dim_ordering='th'
or 4D tensor with shape:
`(1, rows, cols, channels)` if dim_ordering='tf'.
X_roi:
`(1,num_rois,4)` list of rois, with ordering (x,y,w,h)
# Output shape
3D tensor with shape:
`(1, num_rois, channels, pool_size, pool_size)`
'''
def __init__(self, pool_size, num_rois, **kwargs):
self.dim_ordering = K.common.image_dim_ordering()
assert self.dim_ordering in {'tf', 'th'}, 'dim_ordering must be in {tf, th}'
self.pool_size = pool_size
self.num_rois = num_rois
super(RoiPoolingConv, self).__init__(**kwargs)
def build(self, input_shape):
if self.dim_ordering == 'th':
self.nb_channels = input_shape[0][1]
elif self.dim_ordering == 'tf':
self.nb_channels = input_shape[0][3]
def compute_output_shape(self, input_shape):
if self.dim_ordering == 'th':
return None, self.num_rois, self.nb_channels, self.pool_size, self.pool_size
else:
return None, self.num_rois, self.pool_size, self.pool_size, self.nb_channels
def call(self, x, mask=None):
assert(len(x) == 2)
img = x[0]
rois = x[1]
input_shape = K.shape(img)
outputs = []
for roi_idx in range(self.num_rois):
x = rois[0, roi_idx, 0]
y = rois[0, roi_idx, 1]
w = rois[0, roi_idx, 2]
h = rois[0, roi_idx, 3]
row_length = w / float(self.pool_size)
col_length = h / float(self.pool_size)
num_pool_regions = self.pool_size
#NOTE: the RoiPooling implementation differs between theano and tensorflow due to the lack of a resize op
# in theano. The theano implementation is much less efficient and leads to long compile times
if self.dim_ordering == 'th':
for jy in range(num_pool_regions):
for ix in range(num_pool_regions):
x1 = x + ix * row_length
x2 = x1 + row_length
y1 = y + jy * col_length
y2 = y1 + col_length
x1 = K.cast(x1, 'int32')
x2 = K.cast(x2, 'int32')
y1 = K.cast(y1, 'int32')
y2 = K.cast(y2, 'int32')
x2 = x1 + K.maximum(1,x2-x1)
y2 = y1 + K.maximum(1,y2-y1)
new_shape = [input_shape[0], input_shape[1],
y2 - y1, x2 - x1]
x_crop = img[:, :, y1:y2, x1:x2]
xm = K.reshape(x_crop, new_shape)
pooled_val = K.max(xm, axis=(2, 3))
outputs.append(pooled_val)
elif self.dim_ordering == 'tf':
x = K.cast(x, 'int32')
y = K.cast(y, 'int32')
w = K.cast(w, 'int32')
h = K.cast(h, 'int32')
rs = tf.image.resize(img[:, y:y+h, x:x+w, :], (self.pool_size, self.pool_size))
outputs.append(rs)
final_output = K.concatenate(outputs, axis=0)
final_output = K.reshape(final_output, (1, self.num_rois, self.pool_size, self.pool_size, self.nb_channels))
if self.dim_ordering == 'th':
final_output = K.permute_dimensions(final_output, (0, 1, 4, 2, 3))
else:
final_output = K.permute_dimensions(final_output, (0, 1, 2, 3, 4))
return final_output
def get_config(self):
config = {'pool_size': self.pool_size,
'num_rois': self.num_rois}
base_config = super(RoiPoolingConv, self).get_config()
return dict(list(base_config.items()) + list(config.items()))
The data generator code is as follows
from __future__ import absolute_import
import numpy as np
import cv2
import random
import copy
from . import data_augment
import threading
import itertools
def union(au, bu, area_intersection):
area_a = (au[2] - au[0]) * (au[3] - au[1])
area_b = (bu[2] - bu[0]) * (bu[3] - bu[1])
area_union = area_a + area_b - area_intersection
return area_union
def intersection(ai, bi):
x = max(ai[0], bi[0])
y = max(ai[1], bi[1])
w = min(ai[2], bi[2]) - x
h = min(ai[3], bi[3]) - y
if w < 0 or h < 0:
return 0
return w*h
def iou(a, b):
# a and b should be (x1,y1,x2,y2)
if a[0] >= a[2] or a[1] >= a[3] or b[0] >= b[2] or b[1] >= b[3]:
return 0.0
area_i = intersection(a, b)
area_u = union(a, b, area_i)
return float(area_i) / float(area_u + 1e-6)
def get_new_img_size(width, height, img_min_side=600):
if width <= height:
f = float(img_min_side) / width
resized_height = int(f * height)
resized_width = img_min_side
else:
f = float(img_min_side) / height
resized_width = int(f * width)
resized_height = img_min_side
return resized_width, resized_height
class SampleSelector:
def __init__(self, class_count):
# ignore classes that have zero samples
self.classes = [b for b in class_count.keys() if class_count[b] > 0]
self.class_cycle = itertools.cycle(self.classes)
self.curr_class = next(self.class_cycle)
def skip_sample_for_balanced_class(self, img_data):
class_in_img = False
for bbox in img_data['bboxes']:
cls_name = bbox['class']
if cls_name == self.curr_class:
class_in_img = True
self.curr_class = next(self.class_cycle)
break
if class_in_img:
return False
else:
return True
def calc_rpn(C, img_data, width, height, resized_width, resized_height, img_length_calc_function):
downscale = float(C.rpn_stride)
anchor_sizes = C.anchor_box_scales
anchor_ratios = C.anchor_box_ratios
num_anchors = len(anchor_sizes) * len(anchor_ratios)
# calculate the output map size based on the network architecture
(output_width, output_height) = img_length_calc_function(resized_width, resized_height)
n_anchratios = len(anchor_ratios)
# initialise empty output objectives
y_rpn_overlap = np.zeros((output_height, output_width, num_anchors))
y_is_box_valid = np.zeros((output_height, output_width, num_anchors))
y_rpn_regr = np.zeros((output_height, output_width, num_anchors * 4))
num_bboxes = len(img_data['bboxes'])
num_anchors_for_bbox = np.zeros(num_bboxes).astype(int)
best_anchor_for_bbox = -1*np.ones((num_bboxes, 4)).astype(int)
best_iou_for_bbox = np.zeros(num_bboxes).astype(np.float32)
best_x_for_bbox = np.zeros((num_bboxes, 4)).astype(int)
best_dx_for_bbox = np.zeros((num_bboxes, 4)).astype(np.float32)
# get the GT box coordinates, and resize to account for image resizing
gta = np.zeros((num_bboxes, 4))
for bbox_num, bbox in enumerate(img_data['bboxes']):
# get the GT box coordinates, and resize to account for image resizing
gta[bbox_num, 0] = bbox['x1'] * (resized_width / float(width))
gta[bbox_num, 1] = bbox['x2'] * (resized_width / float(width))
gta[bbox_num, 2] = bbox['y1'] * (resized_height / float(height))
gta[bbox_num, 3] = bbox['y2'] * (resized_height / float(height))
# rpn ground truth
for anchor_size_idx in range(len(anchor_sizes)):
for anchor_ratio_idx in range(n_anchratios):
anchor_x = anchor_sizes[anchor_size_idx] * anchor_ratios[anchor_ratio_idx][0]
anchor_y = anchor_sizes[anchor_size_idx] * anchor_ratios[anchor_ratio_idx][1]
for ix in range(output_width):
# x-coordinates of the current anchor box
x1_anc = downscale * (ix + 0.5) - anchor_x / 2
x2_anc = downscale * (ix + 0.5) + anchor_x / 2
# ignore boxes that go across image boundaries
if x1_anc < 0 or x2_anc > resized_width:
continue
for jy in range(output_height):
# y-coordinates of the current anchor box
y1_anc = downscale * (jy + 0.5) - anchor_y / 2
y2_anc = downscale * (jy + 0.5) + anchor_y / 2
# ignore boxes that go across image boundaries
if y1_anc < 0 or y2_anc > resized_height:
continue
# bbox_type indicates whether an anchor should be a target
bbox_type = 'neg'
# this is the best IOU for the (x,y) coord and the current anchor
# note that this is different from the best IOU for a GT bbox
best_iou_for_loc = 0.0
for bbox_num in range(num_bboxes):
# get IOU of the current GT box and the current anchor box
curr_iou = iou([gta[bbox_num, 0], gta[bbox_num, 2], gta[bbox_num, 1], gta[bbox_num, 3]], [x1_anc, y1_anc, x2_anc, y2_anc])
# calculate the regression targets if they will be needed
if curr_iou > best_iou_for_bbox[bbox_num] or curr_iou > C.rpn_max_overlap:
cx = (gta[bbox_num, 0] + gta[bbox_num, 1]) / 2.0
cy = (gta[bbox_num, 2] + gta[bbox_num, 3]) / 2.0
cxa = (x1_anc + x2_anc)/2.0
cya = (y1_anc + y2_anc)/2.0
tx = (cx - cxa) / (x2_anc - x1_anc)
ty = (cy - cya) / (y2_anc - y1_anc)
tw = np.log((gta[bbox_num, 1] - gta[bbox_num, 0]) / (x2_anc - x1_anc))
th = np.log((gta[bbox_num, 3] - gta[bbox_num, 2]) / (y2_anc - y1_anc))
if img_data['bboxes'][bbox_num]['class'] != 'bg':
# all GT boxes should be mapped to an anchor box, so we keep track of which anchor box was best
if curr_iou > best_iou_for_bbox[bbox_num]:
best_anchor_for_bbox[bbox_num] = [jy, ix, anchor_ratio_idx, anchor_size_idx]
best_iou_for_bbox[bbox_num] = curr_iou
best_x_for_bbox[bbox_num,:] = [x1_anc, x2_anc, y1_anc, y2_anc]
best_dx_for_bbox[bbox_num,:] = [tx, ty, tw, th]
# we set the anchor to positive if the IOU is >0.7 (it does not matter if there was another better box, it just indicates overlap)
if curr_iou > C.rpn_max_overlap:
bbox_type = 'pos'
num_anchors_for_bbox[bbox_num] += 1
# we update the regression layer target if this IOU is the best for the current (x,y) and anchor position
if curr_iou > best_iou_for_loc:
best_iou_for_loc = curr_iou
best_regr = (tx, ty, tw, th)
# if the IOU is >0.3 and <0.7, it is ambiguous and no included in the objective
if C.rpn_min_overlap < curr_iou < C.rpn_max_overlap:
# gray zone between neg and pos
if bbox_type != 'pos':
bbox_type = 'neutral'
# turn on or off outputs depending on IOUs
if bbox_type == 'neg':
y_is_box_valid[jy, ix, anchor_ratio_idx + n_anchratios * anchor_size_idx] = 1
y_rpn_overlap[jy, ix, anchor_ratio_idx + n_anchratios * anchor_size_idx] = 0
elif bbox_type == 'neutral':
y_is_box_valid[jy, ix, anchor_ratio_idx + n_anchratios * anchor_size_idx] = 0
y_rpn_overlap[jy, ix, anchor_ratio_idx + n_anchratios * anchor_size_idx] = 0
elif bbox_type == 'pos':
y_is_box_valid[jy, ix, anchor_ratio_idx + n_anchratios * anchor_size_idx] = 1
y_rpn_overlap[jy, ix, anchor_ratio_idx + n_anchratios * anchor_size_idx] = 1
start = 4 * (anchor_ratio_idx + n_anchratios * anchor_size_idx)
y_rpn_regr[jy, ix, start:start+4] = best_regr
# we ensure that every bbox has at least one positive RPN region
for idx in range(num_anchors_for_bbox.shape[0]):
if num_anchors_for_bbox[idx] == 0:
# no box with an IOU greater than zero ...
if best_anchor_for_bbox[idx, 0] == -1:
continue
y_is_box_valid[
best_anchor_for_bbox[idx,0], best_anchor_for_bbox[idx,1], best_anchor_for_bbox[idx,2] + n_anchratios *
best_anchor_for_bbox[idx,3]] = 1
y_rpn_overlap[
best_anchor_for_bbox[idx,0], best_anchor_for_bbox[idx,1], best_anchor_for_bbox[idx,2] + n_anchratios *
best_anchor_for_bbox[idx,3]] = 1
start = 4 * (best_anchor_for_bbox[idx,2] + n_anchratios * best_anchor_for_bbox[idx,3])
y_rpn_regr[
best_anchor_for_bbox[idx,0], best_anchor_for_bbox[idx,1], start:start+4] = best_dx_for_bbox[idx, :]
y_rpn_overlap = np.transpose(y_rpn_overlap, (2, 0, 1))
y_rpn_overlap = np.expand_dims(y_rpn_overlap, axis=0)
y_is_box_valid = np.transpose(y_is_box_valid, (2, 0, 1))
y_is_box_valid = np.expand_dims(y_is_box_valid, axis=0)
y_rpn_regr = np.transpose(y_rpn_regr, (2, 0, 1))
y_rpn_regr = np.expand_dims(y_rpn_regr, axis=0)
pos_locs = np.where(np.logical_and(y_rpn_overlap[0, :, :, :] == 1, y_is_box_valid[0, :, :, :] == 1))
neg_locs = np.where(np.logical_and(y_rpn_overlap[0, :, :, :] == 0, y_is_box_valid[0, :, :, :] == 1))
num_pos = len(pos_locs[0])
# one issue is that the RPN has many more negative than positive regions, so we turn off some of the negative
# regions. We also limit it to 256 regions.
num_regions = 256
if len(pos_locs[0]) > num_regions/2:
val_locs = random.sample(range(len(pos_locs[0])), len(pos_locs[0]) - num_regions/2)
y_is_box_valid[0, pos_locs[0][val_locs], pos_locs[1][val_locs], pos_locs[2][val_locs]] = 0
num_pos = num_regions/2
if len(neg_locs[0]) + num_pos > num_regions:
val_locs = random.sample(range(len(neg_locs[0])), len(neg_locs[0]) - num_pos)
y_is_box_valid[0, neg_locs[0][val_locs], neg_locs[1][val_locs], neg_locs[2][val_locs]] = 0
y_rpn_cls = np.concatenate([y_is_box_valid, y_rpn_overlap], axis=1)
y_rpn_regr = np.concatenate([np.repeat(y_rpn_overlap, 4, axis=1), y_rpn_regr], axis=1)
return np.copy(y_rpn_cls), np.copy(y_rpn_regr)
class threadsafe_iter:
"""Takes an iterator/generator and makes it thread-safe by
serializing call to the `next` method of given iterator/generator.
"""
def __init__(self, it):
self.it = it
self.lock = threading.Lock()
def __iter__(self):
return self
def next(self):
with self.lock:
return next(self.it)
def threadsafe_generator(f):
"""A decorator that takes a generator function and makes it thread-safe.
"""
def g(*a, **kw):
return threadsafe_iter(f(*a, **kw))
return g
def get_anchor_gt(all_img_data, class_count, C, img_length_calc_function, backend, mode='train'):
# The following line is not useful with Python 3.5, it is kept for the legacy
# all_img_data = sorted(all_img_data)
sample_selector = SampleSelector(class_count)
while True:
if mode == 'train':
np.random.shuffle(all_img_data)
for img_data in all_img_data:
try:
if C.balanced_classes and sample_selector.skip_sample_for_balanced_class(img_data):
continue
# read in image, and optionally add augmentation
if mode == 'train':
img_data_aug, x_img = data_augment.augment(img_data, C, augment=True)
else:
img_data_aug, x_img = data_augment.augment(img_data, C, augment=False)
(width, height) = (img_data_aug['width'], img_data_aug['height'])
(rows, cols, _) = x_img.shape
assert cols == width
assert rows == height
# get image dimensions for resizing
(resized_width, resized_height) = get_new_img_size(width, height, C.im_size)
# resize the image so that smalles side is length = 600px
x_img = cv2.resize(x_img, (resized_width, resized_height), interpolation=cv2.INTER_CUBIC)
try:
y_rpn_cls, y_rpn_regr = calc_rpn(C, img_data_aug, width, height, resized_width, resized_height, img_length_calc_function)
except:
continue
# Zero-center by mean pixel, and preprocess image
x_img = x_img[:,:, (2, 1, 0)] # BGR -> RGB
x_img = x_img.astype(np.float32)
x_img[:, :, 0] -= C.img_channel_mean[0]
x_img[:, :, 1] -= C.img_channel_mean[1]
x_img[:, :, 2] -= C.img_channel_mean[2]
x_img /= C.img_scaling_factor
x_img = np.transpose(x_img, (2, 0, 1))
x_img = np.expand_dims(x_img, axis=0)
y_rpn_regr[:, y_rpn_regr.shape[1]//2:, :, :] *= C.std_scaling
if backend == 'tf':
x_img = np.transpose(x_img, (0, 2, 3, 1))
y_rpn_cls = np.transpose(y_rpn_cls, (0, 2, 3, 1))
y_rpn_regr = np.transpose(y_rpn_regr, (0, 2, 3, 1))
yield np.copy(x_img), [np.copy(y_rpn_cls), np.copy(y_rpn_regr)], img_data_aug
except Exception as e:
print(e)
continue
It's not easy to create and find it helpful, please like, follow and collect~~~