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Implementation of ViT model based on Keras

Project description

ViT-Keras

This is a package that implements the ViT model based on Keras. The ViT was proposed in the paper "An image is worth 16x16 words: transformers for image recognition at scale". This package uses pre trained weights on the imagenet21K and imagenet2012 datasets, which are in. npz format.

◈ Preconditions

  • Python >= 3.7

  • Keras >= 2.9

Q1: What can you do with this package?

  • Build a pre trained standard specification ViT model.

  • Customize and build any specification ViT model to suit your task.

Q2: How to build a pre trained ViT?

  1. Quickly build a pre trained ViTB16

    from keras_vit.vit import ViT_B16
    vit = ViT_B16()
    

    The pre trained ViT has 4 configurations: ViT_B16, ViT_B32, ViT_L16 and ViT_L32.

    config patch size hiddem dim mlp dim attention heads encoder depth
    ViT_B16 16×16 768 3072 12 12
    ViT_B32 32×32 768 3072 12 12
    ViT_L16 16×16 1024 4096 16 24
    ViT_L32 32×32 1024 4096 16 24

    The "imagenet21k" and "imagenet21k+imagenet2012" are slightly different, as shown in the table below.

    dataset image size classes pre logits known labels
    imagenet21k 224 21843 True False
    imagenet21k+imagenet2012 384 1000 False True
  2. Build ViTB16 with differernt pre trained weights.

    from keras_vit.vit import ViT_B16
    vit_1 = ViT_B16(weights = "imagenet21k")
    vit_2 = ViT_B16(weights="imagenet21k+imagenet2012")
    
  3. Build ViTB16 without pre trained weights

    from keras_vit.vit import ViT_B16
    vit = ViT_B16(pre_trained=False)
    

    The pre training weights file will be downloaded to C:\Users\user_name\. Keras\weights when "pre_trained = True".

  4. Build pre trained ViTB32 with custom parameters

    from keras_vit.vit import ViT_B32
    vit = ViT_B32(
        image_size = 128,
        num_classes = 12, 
        pre_logits = False,
        weights = "imagenet21k",
        )
    

    When you change some model parameters and some layers change, these layers will not load pre trained weights, the unchanged layers will still load pre trained weights. You can use loading_summary() to view specific information.

    vit.loading_summary()
    >>
    Model: "ViT-B-32-128"
    -----------------------------------------------------------------
    layers                             load weights inf
    =================================================================
    patch_embedding                    loaded
    
    add_cls_token                      loaded - imagenet
    
    position_embedding                 not loaded - mismatch
    
    transformer_block_0                loaded - imagenet
    
    transformer_block_1                loaded - imagenet
    
    transformer_block_2                loaded - imagenet
    
    transformer_block_3                loaded - imagenet
    
    transformer_block_4                loaded - imagenet
    
    transformer_block_5                loaded - imagenet
    
    transformer_block_6                loaded - imagenet
    
    transformer_block_7                loaded - imagenet
    
    transformer_block_8                loaded - imagenet
    
    transformer_block_9                loaded - imagenet
    
    transformer_block_10               loaded - imagenet
    
    transformer_block_11               loaded - imagenet
    
    layer_norm                         loaded - imagenet
    
    mlp_head                           not loaded - mismatch
    =================================================================
    

Q3: How to build a custom ViT?

  1. Instantiating ViT classes to build custom ViT models

    from keras_vit.vit import ViT
    vit = ViT(
        image_size = 128,
        patch_size = 36,
        num_classes = 1,
        hidden_dim = 128,
        mlp_dim = 512,
        atten_heads = 32,
        encoder_depth = 4,
        dropout_rate = 0.1,
        activation = "sigmoid",
        pre_logits = True,
        include_mlp_head = True,
        )
    vit.summary()
    
    >>
    Model: "ViT-CUSTOM_SIZE-36-128"
    _________________________________________________________________
     Layer (type)                Output Shape              Param #
    =================================================================
     patch_embedding (PatchEmbed  (None, 9, 128)           497792
     ding)
    
     add_cls_token (AddCLSToken)  (None, 10, 128)          128
    
     position_embedding (AddPosi  (None, 10, 128)          1280
     tionEmbedding)
    
     transformer_block_0 (Transf  (None, 10, 128)          198272
     ormerEncoder)
    
     transformer_block_1 (Transf  (None, 10, 128)          198272
     ormerEncoder)
    
     transformer_block_2 (Transf  (None, 10, 128)          198272
     ormerEncoder)
    
     transformer_block_3 (Transf  (None, 10, 128)          198272
     ormerEncoder)
    
     layer_norm (LayerNormalizat  (None, 10, 128)          256
     ion)
    
     extract_token (Lambda)      (None, 128)               0
    
     pre_logits (Dense)          (None, 128)               16512
    
     mlp_head (Dense)            (None, 1)                 129
    
    =================================================================
    Total params: 1,309,185
    Trainable params: 1,309,185
    Non-trainable params: 0
    _________________________________________________________________==========================
    

    It should be noted that "hidden_dim" should be divisible by "atten_heads". It is best to set "image_size" size that can be evenly divided by "patch_size".

  2. Load pre trained weights for custom model

    from keras_vit import utils, vit
    vit_custom = vit.ViT(
        image_size=128,
        patch_size=8,
        encoder_depth=4
        )
    utils.load_imgnet_weights(vit_custom, "ViT-B_16_imagenet21k.npz")
    vit_custom.loading_summary()
    
    >>
    Model: "ViT-CUSTOM_SIZE-8-128"
    -----------------------------------------------------------------
    layers                             load weights inf
    =================================================================
    patch_embedding                    mismatch
    
    add_cls_token                      loaded - imagenet
    
    position_embedding                 not loaded - mismatch
    
    transformer_block_0                loaded - imagenet
    
    transformer_block_1                loaded - imagenet
    
    transformer_block_2                loaded - imagenet
    
    transformer_block_3                loaded - imagenet
    
    layer_norm                         loaded - imagenet
    
    pre_logits                         loaded - imagenet
    
    mlp_head                           not loaded - mismatch
    =================================================================
    

Q4: Fine tuning or image classification on pre trained ViT ?

  1. Fine tuning pre trained ViT

    from keras_vit.vit import ViT_L16
    
    # Set parameters
    IMAGE_SIZE = ...
    NUM_CLASSES = ...
    ACTIVATION = ...
    ...
    
    # build ViT
    vit = ViT_B32(
        image_size = IMAGE_SIZE,
        num_classes = NUM_CLASSES, 
        activation = ACTIVATION,
        )
    
    # Compiling ViT
    vit.compile(
        optimizer = ...,
        loss = ...,
        metrics = ...
        )
    
    # Define train, valid and test data
    train_generator = ...
    valid_generator = ...
    test_generator  = ...
    
    # fine tuning ViT
    vit.fit(
        x = train_generator ,
        validation_data = valid_generator ,
        steps_per_epoch = ...,
        validation_steps = ...,
        )
    
    # testing
    vit.evaluate(x = test_generator, steps=...)
    
  2. Applying pre trained ViT for Image Classification

    from keras_vit import vit
    from keras_vit import utils
    
    # Get pre-trained vitb16
    vit_model = vit.ViT_B16(weights="imagenet21k+imagenet2012")
    
    # Load a picture
    img = utils.read_img("test.jpg", resize=vit_model.image_size)
    img = img.reshape((1,*vit_model.image_size,3))
    
    # Classifying
    y = vit_model.predict(img)
    classes = utils.get_imagenet2012_classes()
    print(classes[y[0].argmax()])
    

    It should be noted that as there is currently no label for "imagenet21k", please use "imagenet21k+imagenet2012" when applying pre trained ViT. Both "imagenet21k" and "imagenet21k+imagenet2012" are available during the fine-tuning stage.

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