前言
最近在做人脸比对的工作，需要用到人脸关键点检测的算法，比较成熟和通用的一种算法是 MTCNN，可以同时进行人脸框选和关键点检测，对于每张脸输出 5 个关键点，可以用来进行人脸对齐。
问题
刚开始准备对齐人脸图片用于训练人脸比对算法，是使用官方版本的 MTCNN，该版本是基于 Caffe 的 Matlab 接口的，跑起来很慢，差不多要一秒钟一张图片，处理完几万张图片一天就过去了，好在效果不错。
训练完人脸特征提取的网络以后，想要部署整个人脸比对算法，需要进行人脸检测和对齐。用于工业生产，那个版本的 MTCNN 显然不合适了。在 Github 上寻找替代算法，发现有一个从 Facenet 仓库里面拿出来打包成 Python 包的 MTCNN，直接 pip 就装上了，但是，它也很慢，虽然用了 TensorFlow, 没用上 GPU，检测一张 1080P 的图片要 700ms，太慢了。
想法
正好这几天在学习 TensorRT 相关知识，已经成功将人脸特征提取网络转成 onnx 格式，然后用 TensorRT 的 Python 接口部署好了，单张图片耗时从 15ms 减少到 3ms，非常理想的结果！理所当然，想着把 MTCNN 部署在 TensorRT 平台上面。
MTCNN 的 Caffe 模型直接转成 TensorRT 会有问题，主要是 PReLU 不被支持，解决方法是将该操作重写，但是时间不允许，目前只学会了如何调用能够完整转化的模型，还需要继续深入了解模型转化的细节。
解决方案
非常感谢 @jkjung-avt的工作，在他的博客中详细介绍了如何使用 Cython 和 TensorRT 优化 MTCNN。在他的 Github 中，给出了 TensorRT 版本的 MTCNN，并且是使用 Python 接口写的，太符合我的需求了！
下面回顾一下是如何使用该代码完成工作的。
1.将整个项目下载下来，首先在项目根目录下 make ，编译 Cython 模块，生成 pytrt.cpython-36m-x86_64-linux-gnu.so。
2.在 mtcnn 文件夹下 make，生成 create_engines，再运行 ./create_engines，将 PNet, RNet 和 ONet 的模型文件分别转化为 engine 文件，后面可以直接使用这三个文件进行推理。
3.下面就是使用该模型，说实话，作者的代码还没来得及看，代码量较大，需要认真学习。通过作者的博客，还发现了 Jetson Nano 这样的好东西，便宜的深度学习方案，有时间可以玩一下。下面这个文件就是调用生成的 engine 文件提供推理服务了。
'''
mtcnn.py
'''
import cv2
import numpy as np
import pytrt
PIXEL_MEAN = 127.5
PIXEL_SCALE = 0.0078125
def convert_to_1x1(boxes):
"""Convert detection boxes to 1:1 sizes
# Arguments
boxes: numpy array, shape (n,5), dtype=float32
# Returns
boxes_1x1
"""
boxes_1x1 = boxes.copy()
hh = boxes[:, 3] - boxes[:, 1] + 1.
ww = boxes[:, 2] - boxes[:, 0] + 1.
mm = np.maximum(hh, ww)
boxes_1x1[:, 0] = boxes[:, 0] + ww * 0.5 - mm * 0.5
boxes_1x1[:, 1] = boxes[:, 1] + hh * 0.5 - mm * 0.5
boxes_1x1[:, 2] = boxes_1x1[:, 0] + mm - 1.
boxes_1x1[:, 3] = boxes_1x1[:, 1] + mm - 1.
boxes_1x1[:, 0:4] = np.fix(boxes_1x1[:, 0:4])
return boxes_1x1
def crop_img_with_padding(img, box, padding=0):
"""Crop a box from image, with out-of-boundary pixels padded
# Arguments
img: img as a numpy array, shape (H, W, 3)
box: numpy array, shape (5,) or (4,)
padding: integer value for padded pixels
# Returns
cropped_im: cropped image as a numpy array, shape (H, W, 3)
"""
img_h, img_w, _ = img.shape
if box.shape[0] == 5:
cx1, cy1, cx2, cy2, _ = box.astype(int)
elif box.shape[0] == 4:
cx1, cy1, cx2, cy2 = box.astype(int)
else:
raise ValueError
cw = cx2 - cx1 + 1
ch = cy2 - cy1 + 1
cropped_im = np.zeros((ch, cw, 3), dtype=np.uint8) + padding
ex1 = max(0, -cx1) # ex/ey's are the destination coordinates
ey1 = max(0, -cy1)
ex2 = min(cw, img_w - cx1)
ey2 = min(ch, img_h - cy1)
fx1 = max(cx1, 0) # fx/fy's are the source coordinates
fy1 = max(cy1, 0)
fx2 = min(cx2+1, img_w)
fy2 = min(cy2+1, img_h)
cropped_im[ey1:ey2, ex1:ex2, :] = img[fy1:fy2, fx1:fx2, :]
return cropped_im
def nms(boxes, threshold, type='Union'):
"""Non-Maximum Supression
# Arguments
boxes: numpy array [:, 0:5] of [x1, y1, x2, y2, score]'s
threshold: confidence/score threshold, e.g. 0.5
type: 'Union' or 'Min'
# Returns
A list of indices indicating the result of NMS
"""
if boxes.shape[0] == 0:
return []
xx1, yy1, xx2, yy2 = boxes[:, 0], boxes[:, 1], boxes[:, 2], boxes[:, 3]
areas = np.multiply(xx2-xx1+1, yy2-yy1+1)
sorted_idx = boxes[:, 4].argsort()
pick = []
while len(sorted_idx) > 0:
# In each loop, pick the last box (highest score) and remove
# all other boxes with IoU over threshold
tx1 = np.maximum(xx1[sorted_idx[-1]], xx1[sorted_idx[0:-1]])
ty1 = np.maximum(yy1[sorted_idx[-1]], yy1[sorted_idx[0:-1]])
tx2 = np.minimum(xx2[sorted_idx[-1]], xx2[sorted_idx[0:-1]])
ty2 = np.minimum(yy2[sorted_idx[-1]], yy2[sorted_idx[0:-1]])
tw = np.maximum(0.0, tx2 - tx1 + 1)
th = np.maximum(0.0, ty2 - ty1 + 1)
inter = tw * th
if type == 'Min':
iou = inter /
np.minimum(areas[sorted_idx[-1]], areas[sorted_idx[0:-1]])
else:
iou = inter /
(areas[sorted_idx[-1]] + areas[sorted_idx[0:-1]] - inter)
pick.append(sorted_idx[-1])
sorted_idx = sorted_idx[np.where(iou <= threshold)[0]]
return pick
def generate_pnet_bboxes(conf, reg, scale, t):
"""
# Arguments
conf: softmax score (face or not) of each grid
reg: regression values of x1, y1, x2, y2 coordinates.
The values are normalized to grid width (12) and
height (12).
scale: scale-down factor with respect to original image
t: confidence threshold
# Returns
A numpy array of bounding box coordinates and the
cooresponding scores: [[x1, y1, x2, y2, score], ...]
# Notes
Top left corner coordinates of each grid is (x*2, y*2),
or (x*2/scale, y*2/scale) in the original image.
Bottom right corner coordinates is (x*2+12-1, y*2+12-1),
or ((x*2+12-1)/scale, (y*2+12-1)/scale) in the original
image.
"""
conf = conf.T # swap H and W dimensions
dx1 = reg[0, :, :].T
dy1 = reg[1, :, :].T
dx2 = reg[2, :, :].T
dy2 = reg[3, :, :].T
(x, y) = np.where(conf >= t)
if len(x) == 0:
return np.zeros((0, 5), np.float32)
score = np.array(conf[x, y]).reshape(-1, 1) # Nx1
reg = np.array([dx1[x, y], dy1[x, y],
dx2[x, y], dy2[x, y]]).T * 12. # Nx4
topleft = np.array([x, y], dtype=np.float32).T * 2. # Nx2
bottomright = topleft + np.array([11., 11.], dtype=np.float32) # Nx2
boxes = (np.concatenate((topleft, bottomright), axis=1) + reg) / scale
boxes = np.concatenate((boxes, score), axis=1) # Nx5
# filter bboxes which are too small
#boxes = boxes[boxes[:, 2]-boxes[:, 0] >= 12., :]
#boxes = boxes[boxes[:, 3]-boxes[:, 1] >= 12., :]
return boxes
def generate_rnet_bboxes(conf, reg, pboxes, t):
"""
# Arguments
conf: softmax score (face or not) of each box
reg: regression values of x1, y1, x2, y2 coordinates.
The values are normalized to box width and height.
pboxes: input boxes to RNet
t: confidence threshold
# Returns
boxes: a numpy array of box coordinates and cooresponding
scores: [[x1, y1, x2, y2, score], ...]
"""
boxes = pboxes.copy() # make a copy
assert boxes.shape[0] == conf.shape[0]
boxes[:, 4] = conf # update 'score' of all boxes
boxes = boxes[conf >= t, :]
reg = reg[conf >= t, :]
ww = (boxes[:, 2]-boxes[:, 0]+1).reshape(-1, 1) # x2 - x1 + 1
hh = (boxes[:, 3]-boxes[:, 1]+1).reshape(-1, 1) # y2 - y1 + 1
boxes[:, 0:4] += np.concatenate((ww, hh, ww, hh), axis=1) * reg
return boxes
def generate_onet_outputs(conf, reg_boxes, reg_marks, rboxes, t):
"""
# Arguments
conf: softmax score (face or not) of each box
reg_boxes: regression values of x1, y1, x2, y2
The values are normalized to box width and height.
reg_marks: regression values of the 5 facial landmark points
rboxes: input boxes to ONet (already converted to 2x1)
t: confidence threshold
# Returns
boxes: a numpy array of box coordinates and cooresponding
scores: [[x1, y1, x2, y2,... , score], ...]
landmarks: a numpy array of facial landmark coordinates:
[[x1, x2, ..., x5, y1, y2, ..., y5], ...]
"""
boxes = rboxes.copy() # make a copy
assert boxes.shape[0] == conf.shape[0]
boxes[:, 4] = conf
boxes = boxes[conf >= t, :]
reg_boxes = reg_boxes[conf >= t, :]
reg_marks = reg_marks[conf >= t, :]
xx = boxes[:, 0].reshape(-1, 1)
yy = boxes[:, 1].reshape(-1, 1)
ww = (boxes[:, 2]-boxes[:, 0]).reshape(-1, 1)
hh = (boxes[:, 3]-boxes[:, 1]).reshape(-1, 1)
marks = np.concatenate((xx, xx, xx, xx, xx, yy, yy, yy, yy, yy), axis=1)
marks += np.concatenate((ww, ww, ww, ww, ww, hh, hh,
hh, hh, hh), axis=1) * reg_marks
ww = ww + 1
hh = hh + 1
boxes[:, 0:4] += np.concatenate((ww, hh, ww, hh), axis=1) * reg_boxes
return boxes, marks
def clip_dets(dets, img_w, img_h):
"""Round and clip detection (x1, y1, ...) values.
Note we exclude the last value of 'dets' in computation since
it is 'conf'.
"""
dets[:, 0:-1] = np.fix(dets[:, 0:-1])
evens = np.arange(0, dets.shape[1]-1, 2)
odds = np.arange(1, dets.shape[1]-1, 2)
dets[:, evens] = np.clip(dets[:, evens], 0., float(img_w-1))
dets[:, odds] = np.clip(dets[:, odds], 0., float(img_h-1))
return dets
class TrtPNet(object):
"""TrtPNet
Refer to mtcnn/det1_relu.prototxt for calculation of input/output
dimmensions of TrtPNet, as well as input H offsets (for all scales).
The output H offsets are merely input offsets divided by stride (2).
"""
input_h_offsets = (0, 216, 370, 478, 556, 610, 648, 676, 696)
output_h_offsets = (0, 108, 185, 239, 278, 305, 324, 338, 348)
max_n_scales = 9
def __init__(self, engine):
"""__init__
# Arguments
engine: path to the TensorRT engine file
"""
self.trtnet = pytrt.PyTrtMtcnn(engine,
(3, 710, 384),
(2, 350, 187),
(4, 350, 187))
self.trtnet.set_batchsize(1)
def detect(self, img, minsize=40, factor=0.709, threshold=0.7):
"""Detect faces using PNet
# Arguments
img: input image as a RGB numpy array
threshold: confidence threshold
# Returns
A numpy array of bounding box coordinates and the
cooresponding scores: [[x1, y1, x2, y2, score], ...]
"""
if minsize < 40:
raise ValueError("TrtPNet is currently designed with "
"'minsize' >= 40")
if factor > 0.709:
raise ValueError("TrtPNet is currently designed with "
"'factor' <= 0.709")
m = 12.0 / minsize
img_h, img_w, _ = img.shape
minl = min(img_h, img_w) * m
# create scale pyramid
scales = []
while minl >= 12:
scales.append(m)
m *= factor
minl *= factor
if len(scales) > self.max_n_scales: # probably won't happen...
raise ValueError('Too many scales, try increasing minsize '
'or decreasing factor.')
total_boxes = np.zeros((0, 5), dtype=np.float32)
img = (img.astype(np.float32) - PIXEL_MEAN) * PIXEL_SCALE
# stack all scales of the input image vertically into 1 big
# image, and only do inferencing once
im_data = np.zeros((1, 3, 710, 384), dtype=np.float32)
for i, scale in enumerate(scales):
h_offset = self.input_h_offsets[i]
h = int(img_h * scale)
w = int(img_w * scale)
im_data[0, :, h_offset:(h_offset+h), :w] =
cv2.resize(img, (w, h)).transpose((2, 0, 1))
out = self.trtnet.forward(im_data)
# extract outputs of each scale from the big output blob
for i, scale in enumerate(scales):
h_offset = self.output_h_offsets[i]
h = (int(img_h * scale) - 12) // 2 + 1
w = (int(img_w * scale) - 12) // 2 + 1
pp = out['prob1'][0, 1, h_offset:(h_offset+h), :w]
cc = out['boxes'][0, :, h_offset:(h_offset+h), :w]
boxes = generate_pnet_bboxes(pp, cc, scale, threshold)
if boxes.shape[0] > 0:
pick = nms(boxes, 0.5, 'Union')
if len(pick) > 0:
boxes = boxes[pick, :]
if boxes.shape[0] > 0:
total_boxes = np.concatenate((total_boxes, boxes), axis=0)
if total_boxes.shape[0] == 0:
return total_boxes
pick = nms(total_boxes, 0.7, 'Union')
dets = clip_dets(total_boxes[pick, :], img_w, img_h)
return dets
def destroy(self):
self.trtnet.destroy()
self.trtnet = None
class TrtRNet(object):
"""TrtRNet
# Arguments
engine: path to the TensorRT engine (det2) file
"""
def __init__(self, engine):
self.trtnet = pytrt.PyTrtMtcnn(engine,
(3, 24, 24),
(2, 1, 1),
(4, 1, 1))
def detect(self, img, boxes, max_batch=256, threshold=0.7):
"""Detect faces using RNet
# Arguments
img: input image as a RGB numpy array
boxes: detection results by PNet, a numpy array [:, 0:5]
of [x1, y1, x2, y2, score]'s
max_batch: only process these many top boxes from PNet
threshold: confidence threshold
# Returns
A numpy array of bounding box coordinates and the
cooresponding scores: [[x1, y1, x2, y2, score], ...]
"""
if max_batch > 256:
raise ValueError('Bad max_batch: %d' % max_batch)
boxes = boxes[:max_batch] # assuming boxes are sorted by score
if boxes.shape[0] == 0:
return boxes
img_h, img_w, _ = img.shape
boxes = convert_to_1x1(boxes)
crops = np.zeros((boxes.shape[0], 24, 24, 3), dtype=np.uint8)
for i, det in enumerate(boxes):
cropped_im = crop_img_with_padding(img, det)
# NOTE: H and W dimensions need to be transposed for RNet!
crops[i, ...] = cv2.transpose(cv2.resize(cropped_im, (24, 24)))
crops = crops.transpose((0, 3, 1, 2)) # NHWC -> NCHW
crops = (crops.astype(np.float32) - PIXEL_MEAN) * PIXEL_SCALE
self.trtnet.set_batchsize(crops.shape[0])
out = self.trtnet.forward(crops)
pp = out['prob1'][:, 1, 0, 0]
cc = out['boxes'][:, :, 0, 0]
boxes = generate_rnet_bboxes(pp, cc, boxes, threshold)
if boxes.shape[0] == 0:
return boxes
pick = nms(boxes, 0.7, 'Union')
dets = clip_dets(boxes[pick, :], img_w, img_h)
return dets
def destroy(self):
self.trtnet.destroy()
self.trtnet = None
class TrtONet(object):
"""TrtONet
# Arguments
engine: path to the TensorRT engine (det3) file
"""
def __init__(self, engine):
self.trtnet = pytrt.PyTrtMtcnn(engine,
(3, 48, 48),
(2, 1, 1),
(4, 1, 1),
(10, 1, 1))
def detect(self, img, boxes, max_batch=64, threshold=0.7):
"""Detect faces using ONet
# Arguments
img: input image as a RGB numpy array
boxes: detection results by RNet, a numpy array [:, 0:5]
of [x1, y1, x2, y2, score]'s
max_batch: only process these many top boxes from RNet
threshold: confidence threshold
# Returns
dets: boxes and conf scores
landmarks
"""
if max_batch > 64:
raise ValueError('Bad max_batch: %d' % max_batch)
if boxes.shape[0] == 0:
return (np.zeros((0, 5), dtype=np.float32),
np.zeros((0, 10), dtype=np.float32))
boxes = boxes[:max_batch] # assuming boxes are sorted by score
img_h, img_w, _ = img.shape
boxes = convert_to_1x1(boxes)
crops = np.zeros((boxes.shape[0], 48, 48, 3), dtype=np.uint8)
for i, det in enumerate(boxes):
cropped_im = crop_img_with_padding(img, det)
# NOTE: H and W dimensions need to be transposed for RNet!
crops[i, ...] = cv2.transpose(cv2.resize(cropped_im, (48, 48)))
crops = crops.transpose((0, 3, 1, 2)) # NHWC -> NCHW
crops = (crops.astype(np.float32) - PIXEL_MEAN) * PIXEL_SCALE
self.trtnet.set_batchsize(crops.shape[0])
out = self.trtnet.forward(crops)
pp = out['prob1'][:, 1, 0, 0]
cc = out['boxes'][:, :, 0, 0]
mm = out['landmarks'][:, :, 0, 0]
boxes, landmarks = generate_onet_outputs(pp, cc, mm, boxes, threshold)
pick = nms(boxes, 0.7, 'Min')
return (clip_dets(boxes[pick, :], img_w, img_h),
np.fix(landmarks[pick, :]))
def destroy(self):
self.trtnet.destroy()
self.trtnet = None
class TrtMtcnn(object):
"""TrtMtcnn"""
def __init__(self, engine_files):
self.pnet = TrtPNet(engine_files[0])
self.rnet = TrtRNet(engine_files[1])
self.onet = TrtONet(engine_files[2])
def __del__(self):
self.onet.destroy()
self.rnet.destroy()
self.pnet.destroy()
def _detect_1280x720(self, img, minsize):
"""_detec_1280x720()
Assuming 'img' has been resized to less than 1280x720.
"""
# MTCNN model was trained with 'MATLAB' image so its channel
# order is RGB instead of BGR.
img = img[:, :, ::-1] # BGR -> RGB
dets = self.pnet.detect(img, minsize=minsize)
dets = self.rnet.detect(img, dets)
dets, landmarks = self.onet.detect(img, dets)
return dets, landmarks
def detect(self, img, minsize=40):
"""detect()
This function handles rescaling of the input image if it's
larger than 1280x720.
"""
if img is None:
raise ValueError
img_h, img_w, _ = img.shape
scale = min(720. / img_h, 1280. / img_w)
if scale < 1.0:
new_h = int(np.ceil(img_h * scale))
new_w = int(np.ceil(img_w * scale))
img = cv2.resize(img, (new_w, new_h))
minsize = max(int(np.ceil(minsize * scale)), 40)
dets, landmarks = self._detect_1280x720(img, minsize)
if scale < 1.0:
dets[:, :-1] = np.fix(dets[:, :-1] / scale)
landmarks = np.fix(landmarks / scale)
return dets, landmarks
4.然后在需要人脸检测的地方
from mtcnn import TrtMtcnn
mtcnn = TrtMtcnn(mtcnn_engine_file) # 只初始化一次
dets, landmarks = mtcnn.detect(img, minsize=40)
这样就可以进行人脸框选和关键点检测了。
dets 是人脸框 [[x1, y1, x2, y2,... , score], ...]
landmarks 是5个关键点的坐标 [[x1, x2, ..., x5, y1, y2, ..., y5], ...]
5.如果一张图片中有多张脸，希望选取靠近图片中心的脸，通过以下函数返回该脸的索引，原理是计算左上点和右下点和图片中心的距离，取最小的那个。
def find_central_face(img, dets):
h, w, _ = img.shape
min_distance = 1e10
min_distance_index = 0
i = 0
for det in dets:
distance = (
(det[0] - w / 2) * (det[0] - w / 2)
+ (det[1] - h / 2) * (det[1] - h / 2)
+ (det[2] - w / 2) * (det[2] - w / 2)
+ (det[3] - h / 2) * (det[3] - h / 2)
)
if distance < min_distance:
min_distance = distance
min_distance_index = i
i += 1
return min_distance_index
有了 5 个关键点，就可以做人脸对齐了
import cv2
import numpy
class FaceAligner:
def __init__(self):
self.imgSize = [112, 96]
# 96*112 图中标准的5个关键的坐标
self.coord5point = [
[30.2946, 51.6963],
[65.5318, 51.6963],
[48.0252, 71.7366],
[33.5493, 92.3655],
[62.7299, 92.3655],
] # left_eye, right_eye, nose, mouth_left, mouth_right
def transformation_from_points(self, points1, points2):
# 寻找点之间的变换矩阵
points1 = points1.astype(numpy.float64)
points2 = points2.astype(numpy.float64)
c1 = numpy.mean(points1, axis=0)
c2 = numpy.mean(points2, axis=0)
points1 -= c1
points2 -= c2
s1 = numpy.std(points1)
s2 = numpy.std(points2)
points1 /= s1
points2 /= s2
U, S, Vt = numpy.linalg.svd(points1.T * points2)
R = (U * Vt).T
return numpy.vstack(
[
numpy.hstack(((s2 / s1) * R, c2.T - (s2 / s1) * R * c1.T)),
numpy.matrix([0.0, 0.0, 1.0]),
]
)
def warp_im(self, img_im, src_landmarks, dst_landmarks):
# 根据关键点进行变换
pts1 = numpy.float64(
numpy.matrix([[point[0], point[1]] for point in src_landmarks])
)
pts2 = numpy.float64(
numpy.matrix([[point[0], point[1]] for point in dst_landmarks])
)
M = self.transformation_from_points(pts1, pts2)
dst = cv2.warpAffine(img_im, M[:2], (img_im.shape[1], img_im.shape[0]))
return dst
def align(self, img, face_landmarks):
dst = self.warp_im(img, face_landmarks, self.coord5point) # 原图通过关键点变换
crop_im = dst[0: self.imgSize[0], 0: self.imgSize[1]] # 在变换后的图中裁剪需要的尺寸
return crop_im
后面就是使用人脸特征提取器，分别对两张对齐后的人脸提取特征，计算欧氏距离，卡阈值判断结果了。最终加速结果：1080P 图片，只需要 20ms，完美符合需求了！
总结
这是看 TensorRT 的第三天，已经成功使用 TensorRT 对已有模型进行加速了。对 TensorRT 的工作流程比较熟悉了，但是，对于模型转化，操作转化，自定义操作还是一头雾水，必须要认真学习，尤其是 C++ 接口，看着很难，实际上跟 Python 差不多，只是语法比较啰嗦了一点而已。
熟练掌握 TensorRT，以后所有模型都可以放在上面加速，岂不美滋滋。
参考链接
1 https://github.com/kpzhang93/MTCNN_face_detection_alignment
2 https://github.com/ipazc/mtcnn
3 https://github.com/davidsandberg/facenet
4 https://jkjung-avt.github.io/tensorrt-mtcnn/
5 https://github.com/jkjung-avt/tensorrt_demos#mtcnn