utils.py

# import the necessary packages
import tensorflow as tf
from tensorflow.keras import layers

from PIL import Image
from io import BytesIO
import requests
import numpy as np


RESOLUTION = 224

crop_layer = layers.CenterCrop(RESOLUTION, RESOLUTION)
norm_layer = layers.Normalization(
    mean=[0.485 * 255, 0.456 * 255, 0.406 * 255],
    variance=[(0.229 * 255) ** 2, (0.224 * 255) ** 2, (0.225 * 255) ** 2],
)
rescale_layer = layers.Rescaling(scale=1./127.5, offset=-1)


def preprocess_image(image, model_type, size=RESOLUTION):
    # Turn the image into a numpy array and add batch dim.
    image = np.array(image)
    image = tf.expand_dims(image, 0)
    
    # If model type is vit rescale the image to [-1, 1].
    if model_type == "original_vit":
        image = rescale_layer(image)

    # Resize the image using bicubic interpolation.
    resize_size = int((256 / 224) * size)
    image = tf.image.resize(
        image,
        (resize_size, resize_size),
        method="bicubic"
    )

    # Crop the image.
    image = crop_layer(image)

    # If model type is DeiT or DINO normalize the image.
    if model_type != "original_vit":
        image = norm_layer(image)
    
    return image.numpy()
    

def load_image_from_url(url, model_type):
    # Credit: Willi Gierke
    response = requests.get(url)
    image = Image.open(BytesIO(response.content))
    preprocessed_image = preprocess_image(image, model_type)
    return image, preprocessed_image