README.md

Build Image Classification Models with PyTorch

Follow the instructions to build three classic image classification models:

• MLP
• ResNet18
• MLP-Mixer

Basic usage

python main.py --model <model_name> --model_config <path_to_json> --logdir <result_dir> ...

Please see config.py for other command line usage.

Examples

Train MLP model

python main.py --batch_size 128 --model mlp --model_config ./model_configs/mlp.json --epochs 100 --logdir ./train_log/mlp --device cuda

Train ResNet18 model

python main.py --batch_size 128 --model resnet18 --model_config ./model_configs/resnet18.json --epochs 100 --optimizer adam --lr 0.001 --logdir ./train_log/resnet --device cuda

Train MLP-Mixer model

python main.py --batch_size 128 --model mlpmixer --model_config ./model_configs/mlpmixer.json --epochs 15 --lr 0.1 --logdir ./train_log/mixer --device cuda

Results

Comparison of the best results for the three models:

Hyperparameters used by the above models:

Models	Hyperparameters
MLP	default
ResNet18	batch size=64, weight decay=1e-3, number of epochs=100
MLP-Mixer	learning rate=1e-3, embedding dimension=512, number of blocks=6, number of epochs=84

Visualization

The kernels of the first layer of ResNet18

First normalized all the weights of the kernels of the first layer of ResNet18 (map them between 0 and 1), then averaged each $3 \times 3 \times 3$ image in the channel dimension, and finally got 64 $3 \times 3$ grayscale images, as shown in the figure below.

The weights of the first layer of token-mixing MLP in the first block of MLPMixer

The first layer of token-mixing MLP in the first block of MLPMixer has a dimension of $128 \times 64$, so just normalized the weights of this layer (mapping them between 0 and 1) and displayed the result as 128 $8 \times 8$ grayscale images, as shown in the figure below.

Analysis

We can see that the first layer of token-mixing MLP is the same as the first layer of ResNet18 with many pairs of feature detectors with opposite phases. But since token-mixing allows global communication between different spatial locations, there will be some learned features that operate on the entire image, while others operate on smaller regions. In contrast, ResNet18 tends to only learn detectors that act on pixels in local regions of an image.