lemoncoda/bertforocr-continuity-ep5

BERT for OCR cross-page continuity — EP5

This is a binary XLM-RoBERTa/MiniLM classifier fine-tuned to decide whether two adjacent OCR fragments should be merged across a page boundary.

Labels

• 0: not_continuous — do not merge
• 1: continuous — merge

The model output is converted to P(continuous) with softmax. For conservative merging, use P(continuous) > 0.8, equivalent to score = 2P - 1 > 0.6.

Training configuration

• Base model: MoritzLaurer/multilingual-MiniLMv2-L6-mnli-xnli
• Epoch checkpoint: 5
• Training/validation pairs: 18,049 / 2,005
• Learning rate: 2e-5
• Batch size: 8
• Maximum sequence length: 512 tokens
• Boundary character window: previous tail 800, next head 800
• Random seed: 42
• HTML table markup was preserved during training and validation.

Long pairs use boundary-aware truncation: retain the tail tokens of the previous fragment and the head tokens of the next fragment. With two sequences and a 512-token limit, the normal allocation is 254 tokens from each side; unused space from one side is transferred to the other.

Validation results

The values below are measured on the fixed 2,005-pair validation split. This is not an independent test set.

At the default probability threshold of 0.5:

Accuracy	Precision	Recall	F1	TN	FP	FN	TP
0.894	0.878	0.900	0.889	941	118	95	851

At the recommended conservative threshold of 0.8:

Group	N	Precision	Recall	F0.5	FPR	TN	FP	FN	TP
Overall	2,005	0.943	0.809	0.913	4.34%	1,013	46	181	765
Table	1,808	0.946	0.809	0.915	4.63%	865	42	172	729
Text / OCRFlux bench	197	0.900	0.800	0.878	2.63%	148	4	9	36

The OCRFlux bench source group may include some table-like page elements and should not be interpreted as a perfectly pure prose-only subset.

Inference

Use the fine-tuned model as a two-class sequence-pair classifier and reproduce the boundary-aware truncation described above. The merge probability is:

import torch
from transformers import AutoModelForSequenceClassification, AutoTokenizer

model_id = "lemoncoda/bertforocr-continuity-ep5"
tokenizer = AutoTokenizer.from_pretrained(model_id, use_fast=True)
model = AutoModelForSequenceClassification.from_pretrained(model_id).eval()


def encode_boundary_pair(previous: str, following: str, max_length: int = 512):
    previous_ids = tokenizer.encode(previous, add_special_tokens=False)
    following_ids = tokenizer.encode(following, add_special_tokens=False)
    budget = max_length - tokenizer.num_special_tokens_to_add(pair=True)
    previous_budget = budget // 2
    following_budget = budget - previous_budget

    if len(previous_ids) < previous_budget:
        following_budget += previous_budget - len(previous_ids)
    if len(following_ids) < following_budget:
        previous_budget += following_budget - len(following_ids)

    previous_ids = previous_ids[-previous_budget:]
    following_ids = following_ids[:following_budget]
    return tokenizer.prepare_for_model(
        previous_ids,
        following_ids,
        add_special_tokens=True,
        max_length=max_length,
        truncation="longest_first",
        return_tensors="pt",
    )


encoded = encode_boundary_pair(previous_fragment, next_fragment)
with torch.inference_mode():
    probability = torch.softmax(model(**encoded).logits, dim=-1)[0, 1].item()

should_merge = probability > 0.8
score = 2 * probability - 1

For exact project integration, preserve the original HTML markup in table fragments and apply the 800-character previous-tail/next-head windows before tokenization.