我试着用 cv.dnn.readNetFromONNX 加载一个预先训练好的torch模型(准确地说是U2Net)，保存为 onnx 。

但我收到了错误：

error: OpenCV(4.1.2) /io/opencv/modules/dnn/include/opencv2/dnn/dnn.inl.hpp:349: 
 error (-204:Requested object was not found) Required argument "starts" not found 
 into dictionary in function 'get'

这是用Google再现错误的代码：

### get U2Net implementation ###
%cd /content
!git clone https://github.com/shreyas-bk/U-2-Net
### download pre-trained model ###
!gdown --id 1ao1ovG1Qtx4b7EoskHXmi2E9rp5CHLcZ -O /content/U-2-Net/u2net.pth
%cd /content/U-2-Net
### imports ###
from google.colab import files
from model import U2NET
import torch
import os
### create U2Net model from state
model_dir = '/content/U-2-Net/u2net.pth'
net = U2NET(3, 1)
net.load_state_dict(torch.load(model_dir, map_location='cpu'))
net.eval()
### pass to it a dummy input and save to onnx ###
img = torch.randn(1, 3, 320, 320, requires_grad=False)
img = img.to(torch.device('cpu'))