mirror of
https://github.com/ocrmypdf/OCRmyPDF.git
synced 2026-05-07 06:07:58 -04:00
c77ae4b34c
Breaking change for PDF rendering plugins (although none are known to exist). This provides better separation of Ghostscript specific concerns from the generic plugin interface.
580 lines
22 KiB
Python
580 lines
22 KiB
Python
# SPDX-FileCopyrightText: 2022 James R. Barlow
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# SPDX-License-Identifier: MPL-2.0
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"""OCRmyPDF pluggy plugin specification."""
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from __future__ import annotations
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from abc import ABC, abstractmethod
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from argparse import ArgumentParser, Namespace
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from logging import Handler
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from pathlib import Path
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from typing import TYPE_CHECKING, AbstractSet, NamedTuple, Sequence
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import pluggy
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from ocrmypdf import Executor, PdfContext
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from ocrmypdf.helpers import Resolution
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if TYPE_CHECKING:
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from PIL import Image
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# pylint: disable=ungrouped-imports
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from ocrmypdf._jobcontext import PageContext
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from ocrmypdf.pdfinfo import PdfInfo
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# pylint: enable=ungrouped-imports
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hookspec = pluggy.HookspecMarker('ocrmypdf')
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# pylint: disable=unused-argument
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# mypy: disable-error-code=empty-body
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@hookspec(firstresult=True)
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def get_logging_console() -> Handler:
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"""Returns a custom logging handler.
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Generally this is necessary when both logging output and a progress bar are both
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outputting to ``sys.stderr``.
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Note:
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This is a :ref:`firstresult hook<firstresult>`.
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"""
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@hookspec
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def initialize(plugin_manager: pluggy.PluginManager) -> None:
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"""Called when this plugin is first loaded into OCRmyPDF.
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The primary intended use of this is for plugins to check compatibility with other
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plugins and possibly block other blocks, a plugin that wishes to block ocrmypdf's
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built-in optimize plugin could do:
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.. code-block::
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plugin_manager.set_blocked('ocrmypdf.builtin_plugins.optimize')
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It would also be reasonable for an plugin implementation to check if it is unable
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to proceed, for example, because a required dependency is missing. (If the plugin's
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ability to proceed depends on options and arguments, use ``validate`` instead.)
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Raises:
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ocrmypdf.exceptions.ExitCodeException: If options are not acceptable
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and the application should terminate gracefully with an informative
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message and error code.
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Note:
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This hook will be called from the main process, and may modify global state
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before child worker processes are forked.
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"""
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@hookspec
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def add_options(parser: ArgumentParser) -> None:
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"""Allows the plugin to add its own command line and API arguments.
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OCRmyPDF converts command line arguments to API arguments, so adding
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arguments here will cause new arguments to be processed for API calls
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to ``ocrmypdf.ocr``, or when invoked on the command line.
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Note:
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This hook will be called from the main process, and may modify global state
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before child worker processes are forked.
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"""
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@hookspec
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def check_options(options: Namespace) -> None:
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"""Called to ask the plugin to check all of the options.
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The plugin may check if options that it added are valid.
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Warnings or other messages may be passed to the user by creating a logger
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object using ``log = logging.getLogger(__name__)`` and logging to this.
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The plugin may also modify the *options*. All objects that are in options
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must be picklable so they can be marshalled to child worker processes.
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Raises:
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ocrmypdf.exceptions.ExitCodeException: If options are not acceptable
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and the application should terminate gracefully with an informative
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message and error code.
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Note:
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This hook will be called from the main process, and may modify global state
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before child worker processes are forked.
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"""
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@hookspec(firstresult=True)
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def get_executor(progressbar_class) -> Executor:
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"""Called to obtain an object that manages parallel execution.
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This may be used to replace OCRmyPDF's default parallel execution system
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with a third party alternative. For example, you could make OCRmyPDF run in a
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distributed environment.
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OCRmyPDF's executors are analogous to the standard Python executors in
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``conconcurrent.futures``, but they do not work the same way. Executors may
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be reused for different, unrelated batch operations, since all of the context
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for a given job are passed to :meth:`Executor.__call__`.
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Should be of type :class:`Executor` or otherwise conforming to the protocol
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of that call.
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Arguments:
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progressbar_class: A progress bar class, which will be created when
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Note:
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This hook will be called from the main process, and may modify global state
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before child worker processes are forked.
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Note:
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This is a :ref:`firstresult hook<firstresult>`.
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"""
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@hookspec(firstresult=True)
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def get_progressbar_class():
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"""Called to obtain a class that can be used to monitor progress.
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A progress bar is assumed, but this could be used for any type of monitoring.
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The class should follow a tqdm-like protocol. Calling the class should return
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a new progress bar object, which is activated with ``__enter__`` and terminated
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``__exit__``. An update method is called whenever the progress bar is updated.
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Progress bar objects will not be reused; a new one will be created for each
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group of tasks.
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The progress bar is held in the main process/thread and not updated by child
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process/threads. When a child notifies the parent of completed work, the
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parent updates the progress bar.
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The arguments are the same as `tqdm <https://github.com/tqdm/tqdm>`_ accepts.
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Progress bars should never write to ``sys.stdout``, or they will corrupt the
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output if OCRmyPDF writes a PDF to standard output.
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The type of events that OCRmyPDF reports to a progress bar may change in
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minor releases.
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Here is how OCRmyPDF will use the progress bar:
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Example:
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pbar_class = pm.hook.get_progressbar_class()
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with pbar_class(**tqdm_kwargs) as pbar:
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...
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pbar.update(1)
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"""
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@hookspec
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def validate(pdfinfo: PdfInfo, options: Namespace) -> None:
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"""Called to give a plugin an opportunity to review *options* and *pdfinfo*.
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*options* contains the "work order" to process a particular file. *pdfinfo*
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contains information about the input file obtained after loading and
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parsing. The plugin may modify the *options*. For example, you could decide
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that a certain type of file should be treated with ``options.force_ocr = True``
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based on information in its *pdfinfo*.
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Raises:
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ocrmypdf.exceptions.ExitCodeException: If options or pdfinfo are not acceptable
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and the application should terminate gracefully with an informative
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message and error code.
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Note:
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This hook will be called from the main process, and may modify global state
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before child worker processes are forked.
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"""
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@hookspec(firstresult=True)
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def rasterize_pdf_page(
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input_file: Path,
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output_file: Path,
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raster_device: str,
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raster_dpi: Resolution,
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pageno: int,
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page_dpi: Resolution | None,
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rotation: int | None,
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filter_vector: bool,
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stop_on_soft_error: bool,
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) -> Path:
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"""Rasterize one page of a PDF at resolution raster_dpi in canvas units.
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The image is sized to match the integer pixels dimensions implied by
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raster_dpi even if those numbers are noninteger. The image's DPI will
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be overridden with the values in page_dpi.
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Args:
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input_file: The PDF to rasterize.
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output_file: The desired name of the rasterized image.
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raster_device: Type of image to produce at output_file.
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raster_dpi: Resolution in dots per inch at which to rasterize page.
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pageno: Page number to rasterize (beginning at page 1).
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page_dpi: Resolution, overriding output image DPI.
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rotation: Cardinal angle, clockwise, to rotate page.
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filter_vector: If True, remove vector graphics objects.
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stop_on_soft_error: If there is an "soft error" such that PDF page image
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generation can proceed, but may visually differ from the original,
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the implementer of this hook should raise a detailed exception. If
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``False``, continue processing and report by logging it. If the hook
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cannot proceed, it should always raise an exception, regardless of
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this setting. One "soft error" would be a missing font that is
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required to properly rasterize the PDF.
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Returns:
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Path: output_file if successful
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Note:
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This hook will be called from child processes. Modifying global state
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will not affect the main process or other child processes.
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Note:
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This is a :ref:`firstresult hook<firstresult>`.
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"""
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@hookspec(firstresult=True)
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def filter_ocr_image(page: PageContext, image: Image.Image) -> Image.Image:
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"""Called to filter the image before it is sent to OCR.
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This is the image that OCR sees, not what the user sees when they view the
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PDF. In certain modes such as ``--redo-ocr``, portions of the image may be
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masked out to hide them from OCR.
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The main uses of this hook are expected to be hiding content from OCR,
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conditioning images to OCR better with filters, and adjusting images to
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match any constraints imposed by the OCR engine.
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The input image may be color, grayscale, or monochrome, and the
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output image may differ. For example, if you know that a custom OCR engine
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does not care about the color of the text, you could convert the image to
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it to grayscale or monochrome.
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Generally speaking, the output image should be a faithful representation of
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of the input image. You *may* change the pixel width and height of the
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the input image, but you must not change the aspect ratio, and you must
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calculate the DPI of the output image based on the new pixel width and
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height or the OCR text layer will be misaligned with the visual position.
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The built-in Tesseract OCR engine uses this hook itself to downsample
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very large images to fit its constraints.
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Note:
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This hook will be called from child processes. Modifying global state
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will not affect the main process or other child processes.
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Note:
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This is a :ref:`firstresult hook<firstresult>`.
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"""
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@hookspec(firstresult=True)
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def filter_page_image(page: PageContext, image_filename: Path) -> Path:
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"""Called to filter the whole page before it is inserted into the PDF.
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A whole page image is only produced when preprocessing command line arguments
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are issued or when ``--force-ocr`` is issued. If no whole page is image is
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produced for a given page, this function will not be called. This is not
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the image that will be shown to OCR.
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If the function does not want to modify the image, it should return
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``image_filename``. The hook may overwrite ``image_filename`` with a new file.
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The output image should preserve the same physical unit dimensions, that is
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``(width * dpi_x, height * dpi_y)``. That is, if the image is resized, the DPI
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must be adjusted by the reciprocal. If this is not preserved, the PDF page
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will be resized and the OCR layer misaligned. OCRmyPDF does nothing
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to enforce these constraints; it is up to the plugin to do sensible things.
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OCRmyPDF will create the PDF page based on the image format used (unless the
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hook is overridden). If you convert the image to a JPEG, the output page will
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be created as a JPEG, etc. If you change the colorspace, that change will be
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kept. Note that the OCRmyPDF image optimization stage, if enabled, may
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ultimately chose a different format.
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If the return value is a file that does not exist, ``FileNotFoundError``
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will occur. The return value should be a path to a file in the same folder
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as ``image_filename``.
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Note:
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This hook will be called from child processes. Modifying global state
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will not affect the main process or other child processes.
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Note:
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This is a :ref:`firstresult hook<firstresult>`.
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"""
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@hookspec(firstresult=True)
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def filter_pdf_page(page: PageContext, image_filename: Path, output_pdf: Path) -> Path:
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"""Called to convert a filtered whole page image into a PDF.
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A whole page image is only produced when preprocessing command line arguments
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are issued or when ``--force-ocr`` is issued. If no whole page is image is
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produced for a given page, this function will not be called. This is not
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the image that will be shown to OCR. The whole page image is filtered in
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the hook above, ``filter_page_image``, then this function is called for
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PDF conversion.
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This function will only be called when OCRmyPDF runs in a mode such as
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"force OCR" mode where rasterizing of all content is performed.
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Clever things could be done at this stage such as segmenting the page image into
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color regions or vector equivalents.
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The provider of the hook implementation is responsible for ensuring that the
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OCR text layer is aligned with the PDF produced here, or text misalignment
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will result.
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Currently this function must produce a single page PDF or the pipeline will
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fail. If the intent is to remove the PDF, then create a single page empty
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PDF.
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Args:
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page: Context for this page.
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image_filename: Filename of the input image used to create output_pdf,
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for "reference" if recreating the output_pdf entirely.
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output_pdf: The previous created output_pdf.
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Returns:
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output_pdf
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Note:
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This hook will be called from child processes. Modifying global state
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will not affect the main process or other child processes.
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Note:
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This is a :ref:`firstresult hook<firstresult>`.
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"""
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class OrientationConfidence(NamedTuple):
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"""Expresses an OCR engine's confidence in page rotation.
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Attributes:
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angle: The clockwise angle (0, 90, 180, 270) that the page should be
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rotated. 0 means no rotation.
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confidence: How confident the OCR engine is that this the correct
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rotation. 0 is not confident, 15 is very confident. Arbitrary units.
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"""
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angle: int
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confidence: float
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class OcrEngine(ABC):
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"""A class representing an OCR engine with capabilities similar to Tesseract OCR.
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This could be used to create a plugin for another OCR engine instead of
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Tesseract OCR.
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"""
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@staticmethod
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@abstractmethod
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def version() -> str:
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"""Returns the version of the OCR engine."""
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@staticmethod
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@abstractmethod
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def creator_tag(options: Namespace) -> str:
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"""Returns the creator tag to identify this software's role in creating the PDF.
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This tag will be inserted in the XMP metadata and DocumentInfo dictionary
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as appropriate. Ideally you should include the name of the OCR engine and its
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version. The text should not contain line breaks. This is to help developers
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like yourself identify the software that produced this file.
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OCRmyPDF will always prepend its name to this value.
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"""
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@abstractmethod
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def __str__(self):
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"""Returns name of OCR engine and version.
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This is used when OCRmyPDF wants to mention the name of the OCR engine
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to the user, usually in an error message.
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"""
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@staticmethod
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@abstractmethod
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def languages(options: Namespace) -> AbstractSet[str]:
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"""Returns the set of all languages that are supported by the engine.
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Languages are typically given in 3-letter ISO 3166-1 codes, but actually
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can be any value understood by the OCR engine.
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"""
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@staticmethod
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@abstractmethod
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def get_orientation(input_file: Path, options: Namespace) -> OrientationConfidence:
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"""Returns the orientation of the image."""
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@staticmethod
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def get_deskew(input_file: Path, options: Namespace) -> float:
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"""Returns the deskew angle of the image, in degrees."""
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return 0.0
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@staticmethod
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@abstractmethod
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def generate_hocr(
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input_file: Path, output_hocr: Path, output_text: Path, options: Namespace
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) -> None:
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"""Called to produce a hOCR file and sidecar text file."""
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@staticmethod
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@abstractmethod
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def generate_pdf(
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input_file: Path, output_pdf: Path, output_text: Path, options: Namespace
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) -> None:
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"""Called to produce a text only PDF.
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Args:
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input_file: A page image on which to perform OCR.
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output_pdf: The expected name of the output PDF, which must be
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a single page PDF with no visible content of any kind, sized
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to the dimensions implied by the input_file's width, height
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and DPI. The image will be grafted onto the input PDF page.
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output_text: The expected name of a text file containing the
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recognized text.
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options: The command line options.
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"""
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@hookspec(firstresult=True)
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def get_ocr_engine() -> OcrEngine:
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"""Returns an OcrEngine to use for processing this file.
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The OcrEngine may be instantiated multiple times, by both the main process
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and child process.
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Note:
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This is a :ref:`firstresult hook<firstresult>`.
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"""
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@hookspec(firstresult=True)
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def generate_pdfa(
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pdf_pages: list[Path],
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pdfmark: Path,
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output_file: Path,
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context: PdfContext,
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pdf_version: str,
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pdfa_part: str,
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progressbar_class,
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stop_on_soft_error: bool,
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) -> Path:
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"""Generate a PDF/A.
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This API strongly assumes a PDF/A generator with Ghostscript's semantics.
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OCRmyPDF will modify the metadata and possibly linearize the PDF/A after it
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is generated.
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Arguments:
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pdf_pages: A list of one or more filenames, will be merged into output_file.
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pdfmark: A PostScript file intended for Ghostscript with details on
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how to perform the PDF/A conversion.
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output_file: The name of the desired output file.
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context: The current context.
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pdf_version: The minimum PDF version that the output file should be.
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At its own discretion, the PDF/A generator may raise the version,
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but should not lower it.
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pdfa_part: The desired PDF/A compliance level, such as ``'2B'``.
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progressbar_class: The class of a progress bar with a tqdm-like API. An
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instance of this class will be initialized when PDF/A conversion
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begins, using
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``instance = progressbar_class(total: int, desc: str, unit:str)``,
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defining the number of work units, a user-visible description,
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and the name of the work units ("page"). Then ``instance.update()``
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will be called when a work unit is completed. If ``None``, no
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progress information is reported.
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stop_on_soft_error: If there is an "soft error" such that PDF/A generation
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can proceed and produce a valid PDF/A, but output may be invalid or
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may not visually resemble the original, the implementer of this hook
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should raise a detailed exception. If ``False``, continue processing
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and report by logging it. If the hook cannot proceed, it should always
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raise an exception, regardless of this setting.
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Returns:
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Path: If successful, the hook should return ``output_file``.
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Note:
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This is a :ref:`firstresult hook<firstresult>`.
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Note:
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Before version 15.0.0, the ``context`` was not provided and ``compression``
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was provided instead. Plugins should now read the context object to determine
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if compression is requested.
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See Also:
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https://github.com/tqdm/tqdm
|
|
"""
|
|
|
|
|
|
@hookspec(firstresult=True)
|
|
def optimize_pdf(
|
|
input_pdf: Path,
|
|
output_pdf: Path,
|
|
context: PdfContext,
|
|
executor: Executor,
|
|
linearize: bool,
|
|
) -> tuple[Path, Sequence[str]]:
|
|
"""Optimize a PDF after image, OCR and metadata processing.
|
|
|
|
If the input_pdf is a PDF/A, the plugin should modify input_pdf in a way
|
|
that preserves the PDF/A status, or report to the user when this is not possible.
|
|
|
|
If the implementation fails to produce a smaller file than the input file, it
|
|
should return input_pdf instead.
|
|
|
|
A plugin that implements a new optimizer may need to suppress the built-in
|
|
optimizer by implementing an ``initialize`` hook.
|
|
|
|
Arguments:
|
|
input_pdf: The input PDF, which has OCR added.
|
|
output_pdf: The requested filename of the output PDF which should be created
|
|
by this optimization hook.
|
|
context: The current context.
|
|
executor: An initialized executor which may be used during optimization,
|
|
to distribute optimization tasks.
|
|
linearize: If True, OCRmyPDF requires ``optimize_pdf`` to return a linearized,
|
|
also known as fast web view PDF.
|
|
|
|
Returns:
|
|
Path: If optimization is successful, the hook should return ``output_file``.
|
|
If optimization does not produce a smaller file, the hook should return
|
|
``input_file``.
|
|
Sequence[str]: Any comments that the plugin wishes to report to the user,
|
|
especially reasons it was not able to further optimize the file. For
|
|
example, the plugin could report that a required third party was not
|
|
installed, so a specific optimization was not attempted.
|
|
|
|
Note:
|
|
This is a :ref:`firstresult hook<firstresult>`.
|
|
"""
|
|
|
|
|
|
@hookspec(firstresult=True)
|
|
def is_optimization_enabled(context: PdfContext) -> bool:
|
|
"""For a given PdfContext, OCRmyPDF asks the plugin if optimization is enabled.
|
|
|
|
An optimization plugin might be installed and active but could be disabled by
|
|
user settings.
|
|
|
|
If this returns False, OCRmyPDF will take certain actions to finalize the PDF.
|
|
|
|
Returns:
|
|
True if the plugin's optimization is enabled.
|
|
|
|
Note:
|
|
This is a :ref:`firstresult hook<firstresult>`.
|
|
"""
|