Many Class Activation Map methods implemented in Pytorch!

• GradCAM
• GradCAM++
• ScoreCAM
• XGradCAM
• AblationCAM (with a fast batched implementation)

What makes the network think the image label is 'pug, pug-dog' and 'tabby, tabby cat':

Combining Grad-CAM with Guided Backpropagation for the 'pug, pug-dog' class:

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Tested with most of the torchvision models. You need to choose the target layer to compute CAM for. Some common choices can be:

• Resnet18 and 50: model.layer4[-1]
• VGG and densenet161: model.features[-1]
• mnasnet1_0: model.layers[-1]

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Using from code as a library

pip install grad-cam

from pytorch_grad_cam import GradCAM, ScoreCAM, GradCAMPlusPlus, AblationCAM, XGradCAM
from pytorch_grad_cam.utils.image import show_cam_on_image
from torchvision.models import resnet50

model = resnet50(pretrained=True)
target_layer = model.layer4[-1]
input_tensor = # Create an input tensor image for your model..

#Can be GradCAM, ScoreCAM, GradCAMPlusPlus, AblationCAM, XGradCAM
cam = GradCAM(model=model, target_layer=target_layer, use_cuda=args.use_cuda)
grayscale_cam = cam(input_tensor=input_tensor, target_category=1)
visualization = show_cam_on_image(rgb_img, grayscale_cam)

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Running the example script:

Usage: python cam.py --image-path <path_to_image> --method <method>

To use with CUDA: python cam.py --image-path <path_to_image> --use-cuda

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You can choose between:

• GradCAM
• ScoreCAM
• GradCAMPlusPlus
• AblationCAM
• XGradCAM

Some methods like ScoreCAM and AblationCAM require a large number of forward passes, and have a batched implementation.

You can control the batch size with cam.batch_size =

It seems that GradCAM++ is almost the same as GradCAM, in most networks except VGG where the advantage is larger.

Network	Image	GradCAM	GradCAM++	Score-CAM
VGG16
Resnet50

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References

https://arxiv.org/abs/1610.02391 Grad-CAM: Visual Explanations from Deep Networks via Gradient-based Localization Ramprasaath R. Selvaraju, Michael Cogswell, Abhishek Das, Ramakrishna Vedantam, Devi Parikh, Dhruv Batra

https://arxiv.org/abs/1710.11063 Grad-CAM++: Improved Visual Explanations for Deep Convolutional Networks Aditya Chattopadhyay, Anirban Sarkar, Prantik Howlader, Vineeth N Balasubramanian

https://arxiv.org/abs/1910.01279 Score-CAM: Score-Weighted Visual Explanations for Convolutional Neural Networks Haofan Wang, Zifan Wang, Mengnan Du, Fan Yang, Zijian Zhang, Sirui Ding, Piotr Mardziel, Xia Hu

https://ieeexplore.ieee.org/abstract/document/9093360/ Saurabh Desai and Harish G Ramaswamy. Ablation-cam: Visual explanations for deep convolutional network via gradient-free localization. In WACV, pages 972–980, 2020

https://arxiv.org/abs/2008.02312 Axiom-based Grad-CAM: Towards Accurate Visualization and Explanation of CNNs Ruigang Fu, Qingyong Hu, Xiaohu Dong, Yulan Guo, Yinghui Gao, Biao Li