Improve the performance of table-extraction by judging whether to do …

[monchin]

…"make_chars" or "make_edges" by checking strategy

Motivation

Hello, I used viztracer to do some table-extraction tests, and found that make_chars and make_edges would always be run whatever the strategy is, which would waste a lot time. So I change the code to run make_chars only if the strategies include "text" and run make_edges only if the strategies include "lines"/"lines_strict"

Below is my test code

from pathlib import Path

p = Path("my-test-pdf.pdf")

import pymupdf
from pymupdf import Document
from pymupdf.table import *
from viztracer import VizTracer



def new_find_tables(
    page,
    clip=None,
    vertical_strategy: str = "lines",
    horizontal_strategy: str = "lines",
    vertical_lines: list = None,
    horizontal_lines: list = None,
    snap_tolerance: float = DEFAULT_SNAP_TOLERANCE,
    snap_x_tolerance: float = None,
    snap_y_tolerance: float = None,
    join_tolerance: float = DEFAULT_JOIN_TOLERANCE,
    join_x_tolerance: float = None,
    join_y_tolerance: float = None,
    edge_min_length: float = 3,
    min_words_vertical: float = DEFAULT_MIN_WORDS_VERTICAL,
    min_words_horizontal: float = DEFAULT_MIN_WORDS_HORIZONTAL,
    intersection_tolerance: float = 3,
    intersection_x_tolerance: float = None,
    intersection_y_tolerance: float = None,
    text_tolerance=3,
    text_x_tolerance=3,
    text_y_tolerance=3,
    strategy=None,  # offer abbreviation
    add_lines=None,  # user-specified lines
    add_boxes=None,  # user-specified rectangles
    paths=None,  # accept vector graphics as parameter
):
    pymupdf._warn_layout_once()
    global CHARS, EDGES
    CHARS = []
    EDGES = []
    old_small = bool(pymupdf.TOOLS.set_small_glyph_heights())  # save old value
    pymupdf.TOOLS.set_small_glyph_heights(True)  # we need minimum bboxes
    if page.rotation != 0:
        page, old_xref, old_rot, old_mediabox = page_rotation_set0(page)
    else:
        old_xref, old_rot, old_mediabox = None, None, None

    if snap_x_tolerance is None:
        snap_x_tolerance = UNSET
    if snap_y_tolerance is None:
        snap_y_tolerance = UNSET
    if join_x_tolerance is None:
        join_x_tolerance = UNSET
    if join_y_tolerance is None:
        join_y_tolerance = UNSET
    if intersection_x_tolerance is None:
        intersection_x_tolerance = UNSET
    if intersection_y_tolerance is None:
        intersection_y_tolerance = UNSET
    if strategy is not None:
        vertical_strategy = strategy
        horizontal_strategy = strategy

    settings = {
        "vertical_strategy": vertical_strategy,
        "horizontal_strategy": horizontal_strategy,
        "explicit_vertical_lines": vertical_lines,
        "explicit_horizontal_lines": horizontal_lines,
        "snap_tolerance": snap_tolerance,
        "snap_x_tolerance": snap_x_tolerance,
        "snap_y_tolerance": snap_y_tolerance,
        "join_tolerance": join_tolerance,
        "join_x_tolerance": join_x_tolerance,
        "join_y_tolerance": join_y_tolerance,
        "edge_min_length": edge_min_length,
        "min_words_vertical": min_words_vertical,
        "min_words_horizontal": min_words_horizontal,
        "intersection_tolerance": intersection_tolerance,
        "intersection_x_tolerance": intersection_x_tolerance,
        "intersection_y_tolerance": intersection_y_tolerance,
        "text_tolerance": text_tolerance,
        "text_x_tolerance": text_x_tolerance,
        "text_y_tolerance": text_y_tolerance,
    }

    old_quad_corrections = pymupdf.TOOLS.unset_quad_corrections()
    try:
        page.get_layout()
        if page.layout_information:
            pymupdf.TOOLS.unset_quad_corrections(True)
            boxes = [
                pymupdf.Rect(b[:4]) for b in page.layout_information if b[-1] == "table"
            ]
        else:
            boxes = []

        if boxes:  # layout did find some tables
            pass
        elif page.layout_information is not None:
            # layout was executed but found no tables
            # make sure we exit quickly with an empty TableFinder
            tbf = TableFinder(page)
            return tbf

        tset = TableSettings.resolve(settings=settings)
        page.table_settings = tset

        if tset.vertical_strategy == "text" or tset.horizontal_strategy == "text":
            make_chars(page, clip=clip)  # create character list of page
        if tset.vertical_strategy.startswith("lines") or tset.horizontal_strategy.startswith(
            "lines"
        ):
            make_edges(
                page,
                clip=clip,
                tset=tset,
                paths=paths,
                add_lines=add_lines,
                add_boxes=add_boxes,
            )  # create lines and curves

        tbf = TableFinder(page, settings=tset)

        if boxes:
            # only keep Finder tables that match a layout box
            tbf.tables = [
                tab
                for tab in tbf.tables
                if any(_iou(tab.bbox, r) >= 0.6 for r in boxes)
            ]
        # build the complementary list of layout table boxes
        my_boxes = [
            r for r in boxes if all(_iou(r, tab.bbox) < 0.6 for tab in tbf.tables)
        ]
        if my_boxes:
            word_rects = [pymupdf.Rect(w[:4]) for w in TEXTPAGE.extractWORDS()]
            tp2 = page.get_textpage(flags=TABLE_DETECTOR_FLAGS)
        for rect in my_boxes:
            cells = make_table_from_bbox(tp2, word_rects, rect)  # pylint: disable=E0606
            tbf.tables.append(Table(page, cells))
    except Exception as e:
        pymupdf.message("find_tables: exception occurred: %s" % str(e))
        return None
    finally:
        pymupdf.TOOLS.set_small_glyph_heights(old_small)
        if old_xref is not None:
            page = page_rotation_reset(page, old_xref, old_rot, old_mediabox)
        pymupdf.TOOLS.unset_quad_corrections(old_quad_corrections)

    return tbf


def test():
    with Document(p) as doc:
        page = doc[0]
        with VizTracer(output_file="result.json"):
            old_tab_lines = page.find_tables()
            new_tab_lines = new_find_tables(page)
            
            old_tab_text = page.find_tables(vertical_strategy="text", horizontal_strategy="text")
            new_tab_text = new_find_tables(page, vertical_strategy="text", horizontal_strategy="text")

    
    assert len(old_tab_lines.tables) == 1
    assert old_tab_lines.cells == new_tab_lines.cells

    assert len(old_tab_text.tables) == 1
    assert old_tab_text.cells == new_tab_text.cells



if __name__ == "__main__":
    test()

From the result.json (checked by "vizviewer result.json"), we can see the performance improves a lot when "lines" and "text" strategies do not appear simultaneously.

"result.json" is too large to upload, so I paste a picture here. Old find_tables costs about 190ms and new find_tables costs about 101ms when both using default "lines" strategy.

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