evaluation.py

"""
Tool to metrics calculation through data and label (string and string).
 * Calculation from Optical Character Recognition (OCR) metrics with editdistance.
"""

import string
import unicodedata
import editdistance
import numpy as np


def ocr_metrics(predicts, ground_truth, norm_accentuation=False, norm_punctuation=False):
    """Calculate Character Error Rate (CER), Word Error Rate (WER) and Sequence Error Rate (SER)"""

    if len(predicts) == 0 or len(ground_truth) == 0:
        return (1, 1, 1)

    cer, wer, ser = [], [], []

    for (pd, gt) in zip(predicts, ground_truth):
        if norm_accentuation:
            pd = unicodedata.normalize("NFKD", pd).encode("ASCII", "ignore").decode("ASCII")
            gt = unicodedata.normalize("NFKD", gt).encode("ASCII", "ignore").decode("ASCII")

        if norm_punctuation:
            pd = pd.translate(str.maketrans("", "", string.punctuation))
            gt = gt.translate(str.maketrans("", "", string.punctuation))

        pd_cer, gt_cer = list(pd), list(gt)
        dist = editdistance.eval(pd_cer, gt_cer)
        cer.append(dist / (max(len(pd_cer), len(gt_cer))))

        pd_wer, gt_wer = pd.split(), gt.split()
        dist = editdistance.eval(pd_wer, gt_wer)
        wer.append(dist / (max(len(pd_wer), len(gt_wer))))

        pd_ser, gt_ser = [pd], [gt]
        dist = editdistance.eval(pd_ser, gt_ser)
        ser.append(dist / (max(len(pd_ser), len(gt_ser))))

    metrics = [cer, wer, ser]
    metrics = np.mean(metrics, axis=1)

    return metrics