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Is This Part of the Page Text, a Picture or a Line?

From the shape of a block on a scanned page and how much black ink it holds, is it text, a horizontal line, a graphic, a vertical line or a picture? Getting this right is the first step in reading a document automatically.

Use caseTechnologyPredictionModel evaluation

The table

5,473 blocks from scanned documents with height, length, area, eccentricity and black-pixel measures, labelled by block type. It's in Welt's research catalogue as Page Blocks, 5,473 rows by 11 columns, licensed CC BY 4.0. The catalogue measures its signal at 0.78. At 5,473 rows and 10 features, TabICLv2 and Kumo Tabular Medium take the table as it is. The others can't take a table this size, so the walkthrough leaves them out.

Walkthrough

  1. Load it from the catalogue

    Find the table, read its recorded target and print the column names.

    import pandas as pd
    from welt import Client
    
    with Client() as client:
        item = client.research_datasets(q="page blocks", limit=1)["items"][0]
        info = client.research_dataset(item["id"])
        data = client.load_research_dataset(item["id"])
    
    target = info["targets"][0]
    target = target["name"] if isinstance(target, dict) else target
    print([column["name"] for column in info["schema"]], target)
  2. Pick the rows

    Set aside 20 rows to predict at the end, and keep the rest for the models to learn from.

    known = data.dropna(subset=[target])
    new_rows = known.sample(20, random_state=1)
    table = known.drop(new_rows.index)
  3. Compare the models and predict

    The models compete on the same folds against a simple guess, then the top-ranked one is fitted on the whole table. ROC AUC runs from 0.5, a coin toss, to 1, a perfect ranking, and a lower Brier score means the probabilities can be trusted more. The last table puts each prediction next to the real answer.

    with Client() as client:
        evaluation = client.evaluate(table, target, task="classification", seed=7,
                                     models=["tabicl-v2", "kumo-medium"])
        model = evaluation.fit()
    
    print(evaluation.summary()[["name", "rank", "roc_auc_mean", "brier_mean"]])
    features = new_rows.drop(columns=target)
    print(pd.DataFrame({"actual": new_rows[target].values, "predicted": model.predict(features),
                        "probability": model.predict_proba(features).max(axis=1)}))

What you get

A type per blockWith a probability for each type.
Rare blocks checkedPer-class scores show how pictures and lines are handled.
A strong signalThe catalogue measures a high signal.

Try it

Use Open with to run the research datasets notebook in Colab, Kaggle or Jupyter and search for "page blocks", or run the code above after pip install "welt-client[parquet]".