src/image_processing.py

import cv2
import numpy as np
from itertools import groupby


def process_image(image, recognition_input_layer):
    # Text detection models expect an image in grayscale format.
    # IMPORTANT! This model enables reading only one line at time.
    #image = cv2.cvtColor(image, cv2.COLOR_RGB2GRAY)


    # Fetch the shape.
    image_height, _ = image.shape

    # B,C,H,W = batch size, number of channels, height, width.
    _, _, H, W = recognition_input_layer.shape

    # Calculate scale ratio between the input shape height and image height to resize the image.
    scale_ratio = H / image_height

    # Resize the image to expected input sizes.
    resized_image = cv2.resize(
        image, None, fx=scale_ratio, fy=scale_ratio, interpolation=cv2.INTER_AREA
    )

    # Pad the image to match input size, without changing aspect ratio.
    resized_image = np.pad(
        resized_image, ((0, 0), (0, W - resized_image.shape[1])), mode="edge"
    )

    # Reshape to network input shape.
    input_image = resized_image[None, None, :, :]
    
    return input_image


def recognize(image, compiled_model, recognition_input_layer, recognition_output_layer, letters):
    input_image = process_image(image, recognition_input_layer)
    # Run inference on the model
    predictions = compiled_model([input_image])[recognition_output_layer]
    
    # Remove a batch dimension.
    predictions = np.squeeze(predictions)

    # Run the `argmax` function to pick the symbols with the highest probability.
    predictions_indexes = np.argmax(predictions, axis=1)
    
    # Use the `groupby` function to remove concurrent letters, as required by CTC greedy decoding.
    output_text_indexes = list(groupby(predictions_indexes))

    # Remove grouper objects.
    output_text_indexes, _ = np.transpose(output_text_indexes, (1, 0))

    # Remove blank symbols.
    output_text_indexes = output_text_indexes[output_text_indexes != 0]

    # Assign letters to indexes from the output array.
    output_text = [letters[letter_index] for letter_index in output_text_indexes]
    
    return output_text