【YOLOX】用YOLOv5框架YOLOX

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最近在跑YOLO主流框架的对比实验，发现了一个很奇怪的问题，就是同一个数据集，在不同YOLO框架下训练出的结果差距竟然大的离谱。我使用ultralytics公司出品的v5、v3框架跑出的结果精度差距是合理的，然而用该Up主写的Yolov4代码，竟与ultralytics公司出品的v5、v3框架跑出的结果精度能低20-30%，帧率低的离谱。并且YOLOX也是一样结果。虽然不知道为什么，但确实无法进行对比实验，于是只能将Yolov4结构与YoloX结构在Yolov5框架中实现。Yolov4在Yolov5框架中的实现我参考了这个博主的博客，大家有需求可以参考：yolov4_u5版复现。是一系列文章。
下面我来实现将YoloX结构移植到Yolov5框架中，以下是结合网络结构以及YoloX源码进行实现：

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一、新建common_x.py

该python文件存放的是YOLOX中用到的模块，主要包括BaseConv、CSPLayer、Dark，代码如下：

import torch
import torch.nn as nnclass SiLU(nn.Module):"""export-friendly version of nn.SiLU()"""@staticmethoddef forward(x):return x * torch.sigmoid(x)def get_activation(name="silu", inplace=True):if name == "silu":module = nn.SiLU(inplace=inplace)elif name == "relu":module = nn.ReLU(inplace=inplace)elif name == "lrelu":module = nn.LeakyReLU(0.1, inplace=inplace)else:raise AttributeError("Unsupported act type: {}".format(name))return moduleclass BaseConv(nn.Module):"""A Conv2d -> Batchnorm -> silu/leaky relu block"""def __init__(self, in_channels, out_channels, ksize, stride, groups=1, bias=False, act="silu"):super().__init__()# same paddingpad = (ksize - 1) // 2self.conv = nn.Conv2d(in_channels,out_channels,kernel_size=ksize,stride=stride,padding=pad,groups=groups,bias=bias,)self.bn = nn.BatchNorm2d(out_channels)self.act = get_activation(act, inplace=True)def forward(self, x):return self.act(self.bn(self.conv(x)))def fuseforward(self, x):return self.act(self.conv(x))class DWConv(nn.Module):"""Depthwise Conv + Conv"""def __init__(self, in_channels, out_channels, ksize, stride=1, act="silu"):super().__init__()self.dconv = BaseConv(in_channels,in_channels,ksize=ksize,stride=stride,groups=in_channels,act=act,)self.pconv = BaseConv(in_channels, out_channels, ksize=1, stride=1, groups=1, act=act)def forward(self, x):x = self.dconv(x)return self.pconv(x)class Bottleneck(nn.Module):# Standard bottleneckdef __init__(self,in_channels,out_channels,shortcut=True,expansion=0.5,depthwise=False,act="silu",):super().__init__()hidden_channels = int(out_channels * expansion)Conv = DWConv if depthwise else BaseConvself.conv1 = BaseConv(in_channels, hidden_channels, 1, stride=1, act=act)self.conv2 = Conv(hidden_channels, out_channels, 3, stride=1, act=act)self.use_add = shortcut and in_channels == out_channelsdef forward(self, x):y = self.conv2(self.conv1(x))if self.use_add:y = y + xreturn yclass ResLayer(nn.Module):"Residual layer with `in_channels` inputs."def __init__(self, in_channels: int):super().__init__()mid_channels = in_channels // 2self.layer1 = BaseConv(in_channels, mid_channels, ksize=1, stride=1, act="lrelu")self.layer2 = BaseConv(mid_channels, in_channels, ksize=3, stride=1, act="lrelu")def forward(self, x):out = self.layer2(self.layer1(x))return x + outclass SPPBottleneck(nn.Module):"""Spatial pyramid pooling layer used in YOLOv3-SPP"""def __init__(self, in_channels, out_channels, kernel_sizes=(5, 9, 13), activation="silu"):super().__init__()hidden_channels = in_channels // 2self.conv1 = BaseConv(in_channels, hidden_channels, 1, stride=1, act=activation)self.m = nn.ModuleList([nn.MaxPool2d(kernel_size=ks, stride=1, padding=ks // 2)for ks in kernel_sizes])conv2_channels = hidden_channels * (len(kernel_sizes) + 1)self.conv2 = BaseConv(conv2_channels, out_channels, 1, stride=1, act=activation)def forward(self, x):x = self.conv1(x)x = torch.cat([x] + [m(x) for m in self.m], dim=1)x = self.conv2(x)return xclass CSPLayer(nn.Module):"""C3 in yolov5, CSP Bottleneck with 3 convolutions"""def __init__(self,in_channels,out_channels,n=1,shortcut=True,expansion=0.5,depthwise=False,act="silu",):"""Args:in_channels (int): input channels.out_channels (int): output channels.n (int): number of Bottlenecks. Default value: 1."""# ch_in, ch_out, number, shortcut, groups, expansionsuper().__init__()hidden_channels = int(out_channels * expansion)  # hidden channelsself.conv1 = BaseConv(in_channels, hidden_channels, 1, stride=1, act=act)self.conv2 = BaseConv(in_channels, hidden_channels, 1, stride=1, act=act)self.conv3 = BaseConv(2 * hidden_channels, out_channels, 1, stride=1, act=act)module_list = [Bottleneck(hidden_channels, hidden_channels, shortcut, 1.0, depthwise, act=act)for _ in range(n)]self.m = nn.Sequential(*module_list)def forward(self, x):x_1 = self.conv1(x)x_2 = self.conv2(x)x_1 = self.m(x_1)x = torch.cat((x_1, x_2), dim=1)return self.conv3(x)class Dark(nn.Module):def __init__(self, c1, c2, n=1, act="silu"):super().__init__()self.cv1 = BaseConv(c1, c2, 3, 2, act=act)self.cv2 = CSPLayer(c2, c2, n=n, depthwise=False, act=act)def forward(self, x):return self.cv2(self.cv1(x))

二、修改yolo.py

由于YOLOX里面使用的是Decoupled Head解藕头，所以需要重新设计Detect部分，这里参考了这位博主的博客：YOLO v5 引入解耦头部。

这里有一个需要注意的点是：在 class DecoupledHead 当中的 self.gd=0.5 ，这个参数对应中间隐藏层的输出通道数，原博主这里默认的256，yolox源代码里面这里是乘了 width_multiple 用来控制宽度，因此为了同样实现 -s 模型，我把他乘了对应的系数 self.gd 其对应于 yaml 文件中的 width_multiple 参数控制实现yolox的不同版本。因此，如果想要实现 yolox 的 -m -x -l版本，修改yaml的 width_multiple 参数的时候，不要忘记改这里的 self.gd。 这里因为还得修改函数接口等，就暂时以这种形式实现，后续有时间把这修改一下。

将以下代码，放入yolo.py：

class DecoupledHead(nn.Module):def __init__(self, ch=256, nc=80, anchors=()):super().__init__()self.nc = nc  # number of classes# 中间隐藏层的输出通道数比例self.gd = 0.5self.nl = len(anchors)  # number of detection layersself.na = len(anchors[0]) // 2  # number of anchorsc_ = int(ch * self.gd)self.merge = Conv(ch, c_, 1, 1)self.cls_convs1 = Conv(c_, c_, 3, 1, 1)self.cls_convs2 = Conv(c_, c_, 3, 1, 1)self.reg_convs1 = Conv(c_, c_, 3, 1, 1)self.reg_convs2 = Conv(c_, c_, 3, 1, 1)self.cls_preds = nn.Conv2d(c_, self.nc * self.na, 1)self.reg_preds = nn.Conv2d(c_, 4 * self.na, 1)self.obj_preds = nn.Conv2d(c_, 1 * self.na, 1)def forward(self, x):x = self.merge(x)x1 = self.cls_convs1(x)x1 = self.cls_convs2(x1)x1 = self.cls_preds(x1)x2 = self.reg_convs1(x)x2 = self.reg_convs2(x2)x21 = self.reg_preds(x2)x22 = self.obj_preds(x2)out = torch.cat([x21, x22, x1], 1)return outclass Decoupled_Detect(nn.Module):stride = None  # strides computed during buildonnx_dynamic = False  # ONNX export parameterexport = False  # export modedef __init__(self, nc=80, anchors=(), ch=(), inplace=True):  # detection layersuper().__init__()self.nc = nc  # number of classesself.no = nc + 5  # number of outputs per anchorself.nl = len(anchors)  # number of detection layersself.na = len(anchors[0]) // 2  # number of anchorsself.grid = [torch.zeros(1)] * self.nl  # init gridself.anchor_grid = [torch.zeros(1)] * self.nl  # init anchor gridself.register_buffer('anchors', torch.tensor(anchors).float().view(self.nl, -1, 2))  # shape(nl,na,2)self.m = nn.ModuleList(DecoupledHead(x, nc, anchors) for x in ch)self.inplace = inplace  # use in-place ops (e.g. slice assignment)def forward(self, x):z = []  # inference outputfor i in range(self.nl):x[i] = self.m[i](x[i])  # convbs, _, ny, nx = x[i].shape  # x(bs,255,20,20) to x(bs,3,20,20,85)x[i] = x[i].view(bs, self.na, self.no, ny, nx).permute(0, 1, 3, 4, 2).contiguous()if not self.training:  # inferenceif self.onnx_dynamic or self.grid[i].shape[2:4] != x[i].shape[2:4]:self.grid[i], self.anchor_grid[i] = self._make_grid(nx, ny, i)y = x[i].sigmoid()if self.inplace:y[..., 0:2] = (y[..., 0:2] * 2 + self.grid[i]) * self.stride[i]  # xyy[..., 2:4] = (y[..., 2:4] * 2) ** 2 * self.anchor_grid[i]  # whelse:  # for YOLOv5 on AWS Inferentia https://github.com/ultralytics/yolov5/pull/2953xy, wh, conf = y.split((2, 2, self.nc + 1), 4)  # y.tensor_split((2, 4, 5), 4)  # torch 1.8.0xy = (xy * 2 + self.grid[i]) * self.stride[i]  # xywh = (wh * 2) ** 2 * self.anchor_grid[i]  # why = torch.cat((xy, wh, conf), 4)z.append(y.view(bs, -1, self.no))return x if self.training else (torch.cat(z, 1),) if self.export else (torch.cat(z, 1), x)def _make_grid(self, nx=20, ny=20, i=0):d = self.anchors[i].devicet = self.anchors[i].dtypeshape = 1, self.na, ny, nx, 2  # grid shapey, x = torch.arange(ny, device=d, dtype=t), torch.arange(nx, device=d, dtype=t)if check_version(torch.__version__, '1.10.0'):  # torch>=1.10.0 meshgrid workaround for torch>=0.7 compatibilityyv, xv = torch.meshgrid(y, x, indexing='ij')else:yv, xv = torch.meshgrid(y, x)grid = torch.stack((xv, yv), 2).expand(shape) - 0.5  # add grid offset, i.e. y = 2.0 * x - 0.5anchor_grid = (self.anchors[i] * self.stride[i]).view((1, self.na, 1, 1, 2)).expand(shape)return grid, anchor_grid

修改yolo.py中的parse_model函数：
在下面添加BaseConv、CSPLayer、Dark模块
添加Decoupled_Detect模块

三、新建yolox.yaml

新建yolox.yaml

# parameters
nc: 80  # number of classes
depth_multiple: 0.33  # expand model depth
width_multiple: 0.5  # expand layer channels# anchors
anchors:- [12,16, 19,36, 40,28]  # P3/8- [36,75, 76,55, 72,146]  # P4/16- [142,110, 192,243, 459,401]  # P5/32# yolov4l backbone
backbone:# [from, number, module, args][[-1, 1, Focus, [64, 3, 1]],  # 0[-1, 3, Dark, [128]],  # 1-P1/2[-1, 9, Dark, [256]],[-1, 9, Dark, [512]],  # 3-P2/4[-1, 3, Dark, [1024]],]# yolov4l head
# na = len(anchors[0])
head:[[-1, 1, BaseConv, [512, 1, 1]], # 11[-1, 1, nn.Upsample, [None, 2, 'nearest']],[[-1, 3], 1, Concat, [1]],[-1, 3, CSPLayer, [512]], # 16[-1, 1, BaseConv, [256, 1, 1]],[-1, 1, nn.Upsample, [None, 2, 'nearest']],[[-1, 2], 1, Concat, [1]],[-1, 3, CSPLayer, [256]], # 21[-1, 1, BaseConv, [256, 3, 2]],[[-1, 9], 1, Concat, [1]],  # cat[-1, 3, CSPLayer, [512]], # 25[-1, 1, BaseConv, [512, 3, 2]], # route backbone P3[[-1, 5], 1, Concat, [1]],  # cat[-1, 3, CSPLayer, [1024]], # 29[[12,15,18], 1, Decoupled_Detect, [nc, anchors]],   # Detect(P3, P4, P5)]

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四、训练

以上配置完之后，其他操作与训练Yolov5步骤一致，最终训练出来的效果，要比原YoloX训练结果好不少，看起来更加合理，与Yolov5训练结果差距也是在合理范围内。