import torch
model = torch.hub.load('pytorch/vision:v0.10.0', 'densenet121', pretrained=True)
# or any of these variants
# model = torch.hub.load('pytorch/vision:v0.10.0', 'densenet169', pretrained=True)
# model = torch.hub.load('pytorch/vision:v0.10.0', 'densenet201', pretrained=True)
# model = torch.hub.load('pytorch/vision:v0.10.0', 'densenet161', pretrained=True)
model.eval()

所有预训练模型都期望输入图像以相同的方式进行归一化，即形状为 (3 x H x W) 的 3 通道 RGB 图像小批量，其中 H 和 W 期望至少为 224。图像必须加载到 [0, 1] 范围内，然后使用 mean = [0.485, 0.456, 0.406] 和 std = [0.229, 0.224, 0.225] 进行归一化。

这是一个示例执行。

# Download an example image from the pytorch website
import urllib
url, filename = ("https://github.com/pytorch/hub/raw/master/images/dog.jpg", "dog.jpg")
try: urllib.URLopener().retrieve(url, filename)
except: urllib.request.urlretrieve(url, filename)

# sample execution (requires torchvision)
from PIL import Image
from torchvision import transforms
input_image = Image.open(filename)
preprocess = transforms.Compose([
    transforms.Resize(256),
    transforms.CenterCrop(224),
    transforms.ToTensor(),
    transforms.Normalize(mean=[0.485, 0.456, 0.406], std=[0.229, 0.224, 0.225]),
])
input_tensor = preprocess(input_image)
input_batch = input_tensor.unsqueeze(0) # create a mini-batch as expected by the model

# move the input and model to GPU for speed if available
if torch.cuda.is_available():
    input_batch = input_batch.to('cuda')
    model.to('cuda')

with torch.no_grad():
    output = model(input_batch)
# Tensor of shape 1000, with confidence scores over ImageNet's 1000 classes
print(output[0])
# The output has unnormalized scores. To get probabilities, you can run a softmax on it.
probabilities = torch.nn.functional.softmax(output[0], dim=0)
print(probabilities)

# Download ImageNet labels
!wget https://raw.githubusercontent.com/pytorch/hub/master/imagenet_classes.txt

# Read the categories
with open("imagenet_classes.txt", "r") as f:
    categories = [s.strip() for s in f.readlines()]
# Show top categories per image
top5_prob, top5_catid = torch.topk(probabilities, 5)
for i in range(top5_prob.size(0)):
    print(categories[top5_catid[i]], top5_prob[i].item())

模型描述

密集连接卷积网络 (DenseNet)，以一种前馈方式将每一层与其他每一层连接起来。传统的 L 层卷积网络有 L 个连接，即每一层与其后续层之间有一个连接，而我们的网络有 L(L+1)/2 个直接连接。对于每一层，其所有前驱层的特征图都被用作输入，并且其自身的特征图也被用作所有后续层的输入。DenseNets 具有多项引人注目的优势：它们缓解了梯度消失问题，增强了特征传播，鼓励了特征复用，并显著减少了参数数量。

使用预训练模型在 ImageNet 数据集上的 1-crop 错误率如下所示。

模型结构 Top-1 错误率 Top-5 错误率
densenet121 25.35 7.83
densenet169 24.00 7.00
densenet201 22.80 6.43
densenet161 22.35 6.20

参考文献