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DOI

PyTorch implementation of HMAX

PyTorch implementation of the HMAX model that closely follows that of the MATLAB implementation of The Laboratory for Computational Cognitive Neuroscience:

http://maxlab.neuro.georgetown.edu/hmax.html

The S and C units of the HMAX model can almost be mapped directly onto TorchVision's Conv2d and MaxPool2d layers, where channels are used to store the filters for different orientations. However, HMAX also implements multiple scales, which doesn't map nicely onto the existing TorchVision functionality. Therefore, each scale has its own Conv2d layer, which are executed in parallel.

Here is a schematic overview of the network architecture:

layers consisting of units with increasing scale
S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1 S1
 \ /   \ /   \ /   \ /   \ /   \ /   \ /   \ /
  C1    C1    C1    C1    C1    C1    C1    C1
   \     \     \    |     /     /     /     /
           ALL-TO-ALL CONNECTIVITY
   /     /     /    |     \     \     \     \
  S2    S2    S2    S2    S2    S2    S2    S2
   |     |     |     |     |     |     |     |
  C2    C2    C2    C2    C2    C2    C2    C2

Installation

This script depends on the NumPy, SciPy, PyTorch and TorchVision packages.

Clone the repository somewhere and run the example.py script:

git clone https://github.com/wmvanvliet/pytorch_hmax
python example.py

Usage

See the example.py script on how to run the model on 10 example images.

Explanation of the output

The hmax.get_all_layers method returns a 4-tuple: s1, c1, s2, c2. Here is a detailed explanation of the dimensions of each of these variables:

s1

These are the first simple units in the model, that perform a 2D convolution with Gabor filters. There are 4 Gabor filters, oriented at 90, -45, 0 and 45 degrees. Each filter is defined at 16 different scales. The s1 variable is a list of length 16, containing the output at each scale. Each element is a NumPy array of shape #images x #rotations x image_height x image_width that is the result of the convolution operation.

c1

The output of the s1 units is processed by the c1 units, which perform a maxpool operation. This is done in 8 scales (pooling across a different number of pixels). The c1 variable is alist of lengh 8, containing the output at each s1 scale. Each element is a NumPy array of shape #images x #rotations x height x width.

s2

The output of the c1 units is processed by the s2 units, which perform 2D convolution again (not with Gabor filters this time, but pre-trained filters loaded from the universal_patch_set.mat file). This is done in 8 scales, operating on each of the 8 scales of the c1 output. The s2 variable is a list of lengh 8, containing the output at each scale. Each element is again a list of length 8, matching the 8 scales of the c1 units. The elements of this list are NumPy arrays of shape #images x #filters x height x width containing the convolution output.

c2

The output of the s2 units is processed by the c2 units, which perform a maxpool operation for each s2 filter. The c2 variable is a list of length 8, containing the output at each s2 scale. Each element is a NumPy array of shape #images x #filters containing the result of the maxpool operation.