Source code for captum.attr._core.layer.grad_cam

#!/usr/bin/env python3
from typing import Any, Callable, List, Tuple, Union

import torch
import torch.nn.functional as F
from torch import Tensor
from torch.nn import Module

from captum._utils.common import (
    _format_additional_forward_args,
    _format_input,
    _format_output,
)
from captum._utils.gradient import (
    apply_gradient_requirements,
    compute_layer_gradients_and_eval,
    undo_gradient_requirements,
)
from captum._utils.typing import TargetType
from captum.attr._utils.attribution import GradientAttribution, LayerAttribution
from captum.log import log_usage


[docs]class LayerGradCam(LayerAttribution, GradientAttribution): r""" Computes GradCAM attribution for chosen layer. GradCAM is designed for convolutional neural networks, and is usually applied to the last convolutional layer. GradCAM computes the gradients of the target output with respect to the given layer, averages for each output channel (dimension 2 of output), and multiplies the average gradient for each channel by the layer activations. The results are summed over all channels. Note that in the original GradCAM algorithm described in the paper, ReLU is applied to the output, returning only non-negative attributions. For providing more flexibility to the user, we choose to not perform the ReLU internally by default and return the sign information. To match the original GradCAM algorithm, it is necessary to pass the parameter relu_attributions=True to apply ReLU on the final attributions or alternatively only visualize the positive attributions. Note: this procedure sums over the second dimension (# of channels), so the output of GradCAM attributions will have a second dimension of 1, but all other dimensions will match that of the layer output. GradCAM attributions are generally upsampled and can be viewed as a mask to the input, since a convolutional layer output generally matches the input image spatially. This upsampling can be performed using LayerAttribution.interpolate, as shown in the example below. More details regarding the GradCAM method can be found in the original paper here: https://arxiv.org/pdf/1610.02391.pdf """ def __init__( self, forward_func: Callable, layer: Module, device_ids: Union[None, List[int]] = None, ) -> None: r""" Args: forward_func (callable): The forward function of the model or any modification of it layer (torch.nn.Module): Layer for which attributions are computed. Output size of attribute matches this layer's output dimensions, except for dimension 2, which will be 1, since GradCAM sums over channels. device_ids (list(int)): Device ID list, necessary only if forward_func applies a DataParallel model. This allows reconstruction of intermediate outputs from batched results across devices. If forward_func is given as the DataParallel model itself, then it is not necessary to provide this argument. """ LayerAttribution.__init__(self, forward_func, layer, device_ids) GradientAttribution.__init__(self, forward_func)
[docs] @log_usage() def attribute( self, inputs: Union[Tensor, Tuple[Tensor, ...]], target: TargetType = None, additional_forward_args: Any = None, attribute_to_layer_input: bool = False, relu_attributions: bool = False, ) -> Union[Tensor, Tuple[Tensor, ...]]: r""" Args: inputs (tensor or tuple of tensors): Input for which attributions are computed. If forward_func takes a single tensor as input, a single input tensor should be provided. If forward_func takes multiple tensors as input, a tuple of the input tensors should be provided. It is assumed that for all given input tensors, dimension 0 corresponds to the number of examples, and if multiple input tensors are provided, the examples must be aligned appropriately. target (int, tuple, tensor or list, optional): Output indices for which gradients are computed (for classification cases, this is usually the target class). If the network returns a scalar value per example, no target index is necessary. For general 2D outputs, targets can be either: - a single integer or a tensor containing a single integer, which is applied to all input examples - a list of integers or a 1D tensor, with length matching the number of examples in inputs (dim 0). Each integer is applied as the target for the corresponding example. For outputs with > 2 dimensions, targets can be either: - A single tuple, which contains #output_dims - 1 elements. This target index is applied to all examples. - A list of tuples with length equal to the number of examples in inputs (dim 0), and each tuple containing #output_dims - 1 elements. Each tuple is applied as the target for the corresponding example. Default: None additional_forward_args (any, optional): If the forward function requires additional arguments other than the inputs for which attributions should not be computed, this argument can be provided. It must be either a single additional argument of a Tensor or arbitrary (non-tuple) type or a tuple containing multiple additional arguments including tensors or any arbitrary python types. These arguments are provided to forward_func in order following the arguments in inputs. Note that attributions are not computed with respect to these arguments. Default: None attribute_to_layer_input (bool, optional): Indicates whether to compute the attributions with respect to the layer input or output. If `attribute_to_layer_input` is set to True then the attributions will be computed with respect to the layer input, otherwise it will be computed with respect to layer output. Note that currently it is assumed that either the input or the outputs of internal layers, depending on whether we attribute to the input or output, are single tensors. Support for multiple tensors will be added later. Default: False relu_attributions (bool, optional): Indicates whether to apply a ReLU operation on the final attribution, returning only non-negative attributions. Setting this flag to True matches the original GradCAM algorithm, otherwise, by default, both positive and negative attributions are returned. Default: False Returns: *tensor* or tuple of *tensors* of **attributions**: - **attributions** (*tensor* or tuple of *tensors*): Attributions based on GradCAM method. Attributions will be the same size as the output of the given layer, except for dimension 2, which will be 1 due to summing over channels. Attributions are returned in a tuple if the layer inputs / outputs contain multiple tensors, otherwise a single tensor is returned. Examples:: >>> # ImageClassifier takes a single input tensor of images Nx3x32x32, >>> # and returns an Nx10 tensor of class probabilities. >>> # It contains a layer conv4, which is an instance of nn.conv2d, >>> # and the output of this layer has dimensions Nx50x8x8. >>> # It is the last convolution layer, which is the recommended >>> # use case for GradCAM. >>> net = ImageClassifier() >>> layer_gc = LayerGradCam(net, net.conv4) >>> input = torch.randn(2, 3, 32, 32, requires_grad=True) >>> # Computes layer GradCAM for class 3. >>> # attribution size matches layer output except for dimension >>> # 1, so dimensions of attr would be Nx1x8x8. >>> attr = layer_gc.attribute(input, 3) >>> # GradCAM attributions are often upsampled and viewed as a >>> # mask to the input, since the convolutional layer output >>> # spatially matches the original input image. >>> # This can be done with LayerAttribution's interpolate method. >>> upsampled_attr = LayerAttribution.interpolate(attr, (32, 32)) """ inputs = _format_input(inputs) additional_forward_args = _format_additional_forward_args( additional_forward_args ) gradient_mask = apply_gradient_requirements(inputs) # Returns gradient of output with respect to # hidden layer and hidden layer evaluated at each input. layer_gradients, layer_evals = compute_layer_gradients_and_eval( self.forward_func, self.layer, inputs, target, additional_forward_args, device_ids=self.device_ids, attribute_to_layer_input=attribute_to_layer_input, ) undo_gradient_requirements(inputs, gradient_mask) summed_grads = tuple( torch.mean( layer_grad, dim=tuple(x for x in range(2, len(layer_grad.shape))), keepdim=True, ) if len(layer_grad.shape) > 2 else layer_grad for layer_grad in layer_gradients ) scaled_acts = tuple( torch.sum(summed_grad * layer_eval, dim=1, keepdim=True) for summed_grad, layer_eval in zip(summed_grads, layer_evals) ) if relu_attributions: scaled_acts = tuple(F.relu(scaled_act) for scaled_act in scaled_acts) return _format_output(len(scaled_acts) > 1, scaled_acts)