Your OCR software extracted: "The quick brown fox jumps over the dog."

Decoding BLEU Score: How to Evaluate Text Extraction and Translation from PDFs

In this post, we will break down what BLEU is, how it works mathematically, and—most importantly—how to use it to validate the accuracy of text extracted or translated from PDF files. BLEU is an algorithm for evaluating the quality of text that has been machine-translated or generated from one language to another (or one format to another). Quality is defined as the similarity between the machine's output and that of a human.

from nltk.translate.bleu_score import sentence_bleu, SmoothingFunction reference = [["The", "quick", "brown", "fox", "jumps", "over", "the", "lazy", "dog"]] The "Hypothesis" (What your OCR/LLM extracted from the PDF) hypothesis = ["The", "quick", "brown", "fox", "jumps", "over", "the", "dog"] Apply smoothing to handle missing n-grams smoother = SmoothingFunction().method1 Calculate BLEU (using 1-gram to 4-grams) score = sentence_bleu(reference, hypothesis, smoothing_function=smoother) print(f"BLEU Score: {score:.2f}") # Output: ~0.82