Captum_Recipe.py

"""
Model Interpretability using Captum
===================================

"""


######################################################################
# Captum helps you understand how the data features impact your model
# predictions or neuron activations, shedding light on how your model
# operates.
# 
# Using Captum, you can apply a wide range of state-of-the-art feature
# attribution algorithms such as \ ``Guided GradCam``\  and
# \ ``Integrated Gradients``\  in a unified way.
# 
# In this recipe you will learn how to use Captum to: 
#
# - Attribute the predictions of an image classifier to their corresponding image features. 
# - Visualize the attribution results.
# 


######################################################################
# Before you begin
# ----------------
# 


######################################################################
# Make sure Captum is installed in your active Python environment. Captum
# is available both on GitHub, as a ``pip`` package, or as a ``conda``
# package. For detailed instructions, consult the installation guide at
# https://captum.ai/
# 


######################################################################
# For a model, we use a built-in image classifier in PyTorch. Captum can
# reveal which parts of a sample image support certain predictions made by
# the model.
# 

import torchvision
from torchvision import transforms
from PIL import Image
import requests
from io import BytesIO

model = torchvision.models.resnet18(pretrained=True).eval()

response = requests.get("https://image.freepik.com/free-photo/two-beautiful-puppies-cat-dog_58409-6024.jpg")
img = Image.open(BytesIO(response.content))

center_crop = transforms.Compose([
 transforms.Resize(256),
 transforms.CenterCrop(224),
])

normalize = transforms.Compose([
    transforms.ToTensor(),               # converts the image to a tensor with values between 0 and 1
    transforms.Normalize(                # normalize to follow 0-centered imagenet pixel RGB distribution
     mean=[0.485, 0.456, 0.406],
     std=[0.229, 0.224, 0.225]
    )
])
input_img = normalize(center_crop(img)).unsqueeze(0)


######################################################################
# Computing Attribution
# ---------------------
# 


######################################################################
# Among the top-3 predictions of the models are classes 208 and 283 which
# correspond to dog and cat.
# 
# Let us attribute each of these predictions to the corresponding part of
# the input, using Captum’s \ ``Occlusion``\  algorithm.
# 

from captum.attr import Occlusion 

occlusion = Occlusion(model)

strides = (3, 9, 9)               # smaller = more fine-grained attribution but slower
target=208,                       # Labrador index in ImageNet 
sliding_window_shapes=(3,45, 45)  # choose size enough to change object appearance
baselines = 0                     # values to occlude the image with. 0 corresponds to gray

attribution_dog = occlusion.attribute(input_img,
                                       strides = strides,
                                       target=target,
                                       sliding_window_shapes=sliding_window_shapes,
                                       baselines=baselines)


target=283,                       # Persian cat index in ImageNet 
attribution_cat = occlusion.attribute(input_img,
                                       strides = strides,
                                       target=target,
                                       sliding_window_shapes=sliding_window_shapes,
                                       baselines=0)


######################################################################
# Besides ``Occlusion``, Captum features many algorithms such as
# \ ``Integrated Gradients``\ , \ ``Deconvolution``\ ,
# \ ``GuidedBackprop``\ , \ ``Guided GradCam``\ , \ ``DeepLift``\ , and
# \ ``GradientShap``\ . All of these algorithms are subclasses of
# ``Attribution`` which expects your model as a callable ``forward_func``
# upon initialization and has an ``attribute(...)`` method which returns
# the attribution result in a unified format.
# 
# Let us visualize the computed attribution results in case of images.
# 


######################################################################
# Visualizing the Results
# -----------------------
# 


######################################################################
# Captum’s \ ``visualization``\  utility provides out-of-the-box methods
# to visualize attribution results both for pictorial and for textual
# inputs.
# 

import numpy as np
from captum.attr import visualization as viz

# Convert the compute attribution tensor into an image-like numpy array
attribution_dog = np.transpose(attribution_dog.squeeze().cpu().detach().numpy(), (1,2,0))

vis_types = ["heat_map", "original_image"]
vis_signs = ["all", "all"] # "positive", "negative", or "all" to show both
# positive attribution indicates that the presence of the area increases the prediction score
# negative attribution indicates distractor areas whose absence increases the score

_ = viz.visualize_image_attr_multiple(attribution_dog,
                                      np.array(center_crop(img)),
                                      vis_types,
                                      vis_signs,
                                      ["attribution for dog", "image"],
                                      show_colorbar = True
                                     )


attribution_cat = np.transpose(attribution_cat.squeeze().cpu().detach().numpy(), (1,2,0))

_ = viz.visualize_image_attr_multiple(attribution_cat,
                                      np.array(center_crop(img)),
                                      ["heat_map", "original_image"],  
                                      ["all", "all"], # positive/negative attribution or all
                                      ["attribution for cat", "image"],
                                      show_colorbar = True
                                     )


######################################################################
# If your data is textual, ``visualization.visualize_text()`` offers a
# dedicated view to explore attribution on top of the input text. Find out
# more at http://captum.ai/tutorials/IMDB_TorchText_Interpret
# 


######################################################################
# Final Notes
# -----------
# 


######################################################################
# Captum can handle most model types in PyTorch across modalities
# including vision, text, and more. With Captum you can: \* Attribute a
# specific output to the model input as illustrated above. \* Attribute a
# specific output to a hidden-layer neuron (see Captum API reference). \*
# Attribute a hidden-layer neuron response to the model input (see Captum
# API reference).
# 
# For complete API of the supported methods and a list of tutorials,
# consult our website http://captum.ai
# 
# Another useful post by Gilbert Tanner:
# https://gilberttanner.com/blog/interpreting-pytorch-models-with-captum
#