本文主要針對yolov3-tiny進行講解，具體的網絡結構如下：
可以結合該圖以及對應的.cfg文件，對model.py進行分析網絡結構的具體實現：
from __future__ import division
import torch
import torch.nn as nn
import torch.nn.functional as F
from torch.autograd import Variable
import numpy as np
from utils.parse_config import *
from utils.utils import build_targets, to_cpu, non_max_suppression
import matplotlib.pyplot as plt
import matplotlib.patches as patches
#通過加載的網絡模型參數,創建網絡modules
def create_modules(module_defs):
"""
Constructs module list of layer blocks from module configuration in module_defs
"""
hyperparams = module_defs.pop(0)
output_filters = [int(hyperparams["channels"])]
module_list = nn.ModuleList()
for module_i, module_def in enumerate(module_defs):
modules = nn.Sequential()
if module_def["type"] == "convolutional":
bn = int(module_def["batch_normalize"])
filters = int(module_def["filters"])
kernel_size = int(module_def["size"])
pad = (kernel_size - 1) // 2
modules.add_module(
"conv_{module_i}",
nn.Conv2d(
in_channels=output_filters[-1],
out_channels=filters,
kernel_size=kernel_size,
stride=int(module_def["stride"]),
padding=pad,
bias=not bn,
),
)
if bn:
modules.add_module("batch_norm_{module_i}", nn.BatchNorm2d(filters, momentum=0.9, eps=1e-5))
if module_def["activation"] == "leaky":
modules.add_module("leaky_{module_i}", nn.LeakyReLU(0.1))
elif module_def["type"] == "maxpool":
kernel_size = int(module_def["size"])
stride = int(module_def["stride"])
if kernel_size == 2 and stride == 1:
modules.add_module("_debug_padding_{module_i}", nn.ZeroPad2d((0, 1, 0, 1)))
maxpool = nn.MaxPool2d(kernel_size=kernel_size, stride=stride, padding=int((kernel_size - 1) // 2))
modules.add_module("maxpool_{module_i}", maxpool)
elif module_def["type"] == "upsample":
upsample = Upsample(scale_factor=int(module_def["stride"]), mode="nearest")
modules.add_module("upsample_{module_i}", upsample)
elif module_def["type"] == "route":
layers = [int(x) for x in module_def["layers"].split(",")]
filters = sum([output_filters[1:][i] for i in layers])
modules.add_module("route_{module_i}", EmptyLayer())
elif module_def["type"] == "shortcut":
filters = output_filters[1:][int(module_def["from"])]
modules.add_module("shortcut_{module_i}", EmptyLayer())
elif module_def["type"] == "yolo":
anchor_idxs = [int(x) for x in module_def["mask"].split(",")]
# Extract anchors
anchors = [int(x) for x in module_def["anchors"].split(",")]
anchors = [(anchors[i], anchors[i + 1]) for i in range(0, len(anchors), 2)]
anchors = [anchors[i] for i in anchor_idxs]
num_classes = int(module_def["classes"])
img_size = int(hyperparams["height"])
# Define detection layer
yolo_layer = YOLOLayer(anchors, num_classes, img_size)
modules.add_module("yolo_{module_i}", yolo_layer)
# Register module list and number of output filters
module_list.append(modules)
output_filters.append(filters)
return hyperparams, module_list
#上採樣
class Upsample(nn.Module):
""" nn.Upsample is deprecated """
def __init__(self, scale_factor, mode="nearest"):
super(Upsample, self).__init__()
self.scale_factor = scale_factor
self.mode = mode
def forward(self, x):
x = F.interpolate(x, scale_factor=self.scale_factor, mode=self.mode)
return x
class EmptyLayer(nn.Module):
"""Placeholder for 'route' and 'shortcut' layers"""
def __init__(self):
super(EmptyLayer, self).__init__()
#yolo層的具體實現
class YOLOLayer(nn.Module):
"""Detection layer"""
def __init__(self, anchors, num_classes, img_dim=416):
super(YOLOLayer, self).__init__()
self.anchors = anchors
self.num_anchors = len(anchors)
self.num_classes = num_classes
self.ignore_thres = 0.5
self.mse_loss = nn.MSELoss()
self.bce_loss = nn.BCELoss()
self.obj_scale = 1
self.noobj_scale = 100
self.metrics = {}
self.img_dim = img_dim
self.grid_size = 0 # grid size
#計算網絡的偏移量
def compute_grid_offsets(self, grid_size, cuda=True):
self.grid_size = grid_size
g = self.grid_size
FloatTensor = torch.cuda.FloatTensor if cuda else torch.FloatTensor
self.stride = self.img_dim / self.grid_size
# Calculate offsets for each grid
self.grid_x = torch.arange(g).repeat(g, 1).view([1, 1, g, g]).type(FloatTensor)
self.grid_y = torch.arange(g).repeat(g, 1).t().view([1, 1, g, g]).type(FloatTensor)
self.scaled_anchors = FloatTensor([(a_w / self.stride, a_h / self.stride) for a_w, a_h in self.anchors])
self.anchor_w = self.scaled_anchors[:, 0:1].view((1, self.num_anchors, 1, 1))
self.anchor_h = self.scaled_anchors[:, 1:2].view((1, self.num_anchors, 1, 1))
#前向預測
def forward(self, x, targets=None, img_dim=None):
# Tensors for cuda support
FloatTensor = torch.cuda.FloatTensor if x.is_cuda else torch.FloatTensor
LongTensor = torch.cuda.LongTensor if x.is_cuda else torch.LongTensor
ByteTensor = torch.cuda.ByteTensor if x.is_cuda else torch.ByteTensor
self.img_dim = img_dim
num_samples = x.size(0)
grid_size = x.size(2)
prediction = (
x.view(num_samples, self.num_anchors, self.num_classes + 5, grid_size, grid_size)
.permute(0, 1, 3, 4, 2)
.contiguous()
)
# Get outputs
x = torch.sigmoid(prediction[..., 0]) # Center x
y = torch.sigmoid(prediction[..., 1]) # Center y
w = prediction[..., 2] # Width
h = prediction[..., 3] # Height
pred_conf = torch.sigmoid(prediction[..., 4]) # Conf
pred_cls = torch.sigmoid(prediction[..., 5:]) # Cls pred.
# If grid size does not match current we compute new offsets
if grid_size != self.grid_size:
self.compute_grid_offsets(grid_size, cuda=x.is_cuda)
# Add offset and scale with anchors
pred_boxes = FloatTensor(prediction[..., :4].shape)
pred_boxes[..., 0] = x.data + self.grid_x
pred_boxes[..., 1] = y.data + self.grid_y
pred_boxes[..., 2] = torch.exp(w.data) * self.anchor_w
pred_boxes[..., 3] = torch.exp(h.data) * self.anchor_h
output = torch.cat(
(
pred_boxes.view(num_samples, -1, 4) * self.stride,
pred_conf.view(num_samples, -1, 1),
pred_cls.view(num_samples, -1, self.num_classes),
),
-1,
)
if targets is None:
return output, 0
else:
iou_scores, class_mask, obj_mask, noobj_mask, tx, ty, tw, th, tcls, tconf = build_targets(
pred_boxes=pred_boxes,
pred_cls=pred_cls,
target=targets,
anchors=self.scaled_anchors,
ignore_thres=self.ignore_thres,
)
#通過mask來實現類別,置信度,box的損失計算
# Loss : Mask outputs to ignore non-existing objects (except with conf. loss)
loss_x = self.mse_loss(x[obj_mask], tx[obj_mask])
loss_y = self.mse_loss(y[obj_mask], ty[obj_mask])
loss_w = self.mse_loss(w[obj_mask], tw[obj_mask])
loss_h = self.mse_loss(h[obj_mask], th[obj_mask])
loss_conf_obj = self.bce_loss(pred_conf[obj_mask], tconf[obj_mask])
loss_conf_noobj = self.bce_loss(pred_conf[noobj_mask], tconf[noobj_mask])
loss_conf = self.obj_scale * loss_conf_obj + self.noobj_scale * loss_conf_noobj
loss_cls = self.bce_loss(pred_cls[obj_mask], tcls[obj_mask])
total_loss = loss_x + loss_y + loss_w + loss_h + loss_conf + loss_cls
# Metrics
cls_acc = 100 * class_mask[obj_mask].mean()
conf_obj = pred_conf[obj_mask].mean()
conf_noobj = pred_conf[noobj_mask].mean()
conf50 = (pred_conf > 0.5).float()
iou50 = (iou_scores > 0.5).float()
iou75 = (iou_scores > 0.75).float()
detected_mask = conf50 * class_mask * tconf
precision = torch.sum(iou50 * detected_mask) / (conf50.sum() + 1e-16)
recall50 = torch.sum(iou50 * detected_mask) / (obj_mask.sum() + 1e-16)
recall75 = torch.sum(iou75 * detected_mask) / (obj_mask.sum() + 1e-16)
self.metrics = {
"loss": to_cpu(total_loss).item(),
"x": to_cpu(loss_x).item(),
"y": to_cpu(loss_y).item(),
"w": to_cpu(loss_w).item(),
"h": to_cpu(loss_h).item(),
"conf": to_cpu(loss_conf).item(),
"cls": to_cpu(loss_cls).item(),
"cls_acc": to_cpu(cls_acc).item(),
"recall50": to_cpu(recall50).item(),
"recall75": to_cpu(recall75).item(),
"precision": to_cpu(precision).item(),
"conf_obj": to_cpu(conf_obj).item(),
"conf_noobj": to_cpu(conf_noobj).item(),
"grid_size": grid_size,
}
return output, total_loss
#網絡模型的具體實現
class Darknet(nn.Module):
"""YOLOv3 object detection model"""
def __init__(self, config_path, img_size=416):
super(Darknet, self).__init__()
self.module_defs = parse_model_config(config_path) #加載網絡模型參數
self.hyperparams, self.module_list = create_modules(self.module_defs)
self.yolo_layers = [layer[0] for layer in self.module_list if hasattr(layer[0], "metrics")]
self.img_size = img_size
self.seen = 0
self.header_info = np.array([0, 0, 0, self.seen, 0], dtype=np.int32)
#網絡的前向過程
def forward(self, x, targets=None):
img_dim = x.shape[2]
loss = 0
layer_outputs, yolo_outputs = [], []
for i, (module_def, module) in enumerate(zip(self.module_defs, self.module_list)):
if module_def["type"] in ["convolutional", "upsample", "maxpool"]:
x = module(x)
elif module_def["type"] == "route":
x = torch.cat([layer_outputs[int(layer_i)] for layer_i in module_def["layers"].split(",")], 1)
elif module_def["type"] == "shortcut":
layer_i = int(module_def["from"])
x = layer_outputs[-1] + layer_outputs[layer_i]
elif module_def["type"] == "yolo":
x, layer_loss = module[0](x, targets, img_dim)
loss += layer_loss
yolo_outputs.append(x)
layer_outputs.append(x)
yolo_outputs = to_cpu(torch.cat(yolo_outputs, 1))
return yolo_outputs if targets is None else (loss, yolo_outputs)
#加載網絡模型
def load_darknet_weights(self, weights_path):
"""Parses and loads the weights stored in 'weights_path'"""
# Open the weights file
with open(weights_path, "rb") as f:
header = np.fromfile(f, dtype=np.int32, count=5) # First five are header values
self.header_info = header # Needed to write header when saving weights
self.seen = header[3] # number of images seen during training
weights = np.fromfile(f, dtype=np.float32) # The rest are weights
# Establish cutoff for loading backbone weights
cutoff = None
if "darknet53.conv.74" in weights_path:
cutoff = 75
ptr = 0
for i, (module_def, module) in enumerate(zip(self.module_defs, self.module_list)):
if i == cutoff:
break
if module_def["type"] == "convolutional":
conv_layer = module[0]
if module_def["batch_normalize"]:
# Load BN bias, weights, running mean and running variance
bn_layer = module[1]
num_b = bn_layer.bias.numel() # Number of biases
# Bias
bn_b = torch.from_numpy(weights[ptr : ptr + num_b]).view_as(bn_layer.bias)
bn_layer.bias.data.copy_(bn_b)
ptr += num_b
# Weight
bn_w = torch.from_numpy(weights[ptr : ptr + num_b]).view_as(bn_layer.weight)
bn_layer.weight.data.copy_(bn_w)
ptr += num_b
# Running Mean
bn_rm = torch.from_numpy(weights[ptr : ptr + num_b]).view_as(bn_layer.running_mean)
bn_layer.running_mean.data.copy_(bn_rm)
ptr += num_b
# Running Var
bn_rv = torch.from_numpy(weights[ptr : ptr + num_b]).view_as(bn_layer.running_var)
bn_layer.running_var.data.copy_(bn_rv)
ptr += num_b
else:
# Load conv. bias
num_b = conv_layer.bias.numel()
conv_b = torch.from_numpy(weights[ptr : ptr + num_b]).view_as(conv_layer.bias)
conv_layer.bias.data.copy_(conv_b)
ptr += num_b
# Load conv. weights
num_w = conv_layer.weight.numel()
conv_w = torch.from_numpy(weights[ptr : ptr + num_w]).view_as(conv_layer.weight)
conv_layer.weight.data.copy_(conv_w)
ptr += num_w
#保存網絡模型
def save_darknet_weights(self, path, cutoff=-1):
"""
@:param path - path of the new weights file
@:param cutoff - save layers between 0 and cutoff (cutoff = -1 -> all are saved)
"""
fp = open(path, "wb")
self.header_info[3] = self.seen
self.header_info.tofile(fp)
# Iterate through layers
for i, (module_def, module) in enumerate(zip(self.module_defs[:cutoff], self.module_list[:cutoff])):
if module_def["type"] == "convolutional":
conv_layer = module[0]
# If batch norm, load bn first
if module_def["batch_normalize"]:
bn_layer = module[1]
bn_layer.bias.data.cpu().numpy().tofile(fp)
bn_layer.weight.data.cpu().numpy().tofile(fp)
bn_layer.running_mean.data.cpu().numpy().tofile(fp)
bn_layer.running_var.data.cpu().numpy().tofile(fp)
# Load conv bias
else:
conv_layer.bias.data.cpu().numpy().tofile(fp)
# Load conv weights
conv_layer.weight.data.cpu().numpy().tofile(fp)
fp.close()
水平有限，若有不當之處，請指教，謝謝！