pairs/pair_31/input.txt

#
# The Python Imaging Library.
# $Id$
#
# standard image operations
#
# History:
# 2001-10-20 fl   Created
# 2001-10-23 fl   Added autocontrast operator
# 2001-12-18 fl   Added Kevin's fit operator
# 2004-03-14 fl   Fixed potential division by zero in equalize
# 2005-05-05 fl   Fixed equalize for low number of values
#
# Copyright (c) 2001-2004 by Secret Labs AB
# Copyright (c) 2001-2004 by Fredrik Lundh
#
# See the README file for information on usage and redistribution.
#

import functools
import operator
import re

from . import ExifTags, Image, ImagePalette

#
# helpers


def _border(border):
    if isinstance(border, tuple):
        if len(border) == 2:
            left, top = right, bottom = border
        elif len(border) == 4:
            left, top, right, bottom = border
    else:
        left = top = right = bottom = border
    return left, top, right, bottom


def _color(color, mode):
    if isinstance(color, str):
        from . import ImageColor

        color = ImageColor.getcolor(color, mode)
    return color


def _lut(image, lut):
    if image.mode == "P":
        # FIXME: apply to lookup table, not image data
        msg = "mode P support coming soon"
        raise NotImplementedError(msg)
    elif image.mode in ("L", "RGB"):
        if image.mode == "RGB" and len(lut) == 256:
            lut = lut + lut + lut
        return image.point(lut)
    else:
        msg = f"not supported for mode {image.mode}"
        raise OSError(msg)


#
# actions


def autocontrast(image, cutoff=0, ignore=None, mask=None, preserve_tone=False):
    """
    Maximize (normalize) image contrast. This function calculates a
    histogram of the input image (or mask region), removes ``cutoff`` percent of the
    lightest and darkest pixels from the histogram, and remaps the image
    so that the darkest pixel becomes black (0), and the lightest
    becomes white (255).

    :param image: The image to process.
    :param cutoff: The percent to cut off from the histogram on the low and
                   high ends. Either a tuple of (low, high), or a single
                   number for both.
    :param ignore: The background pixel value (use None for no background).
    :param mask: Histogram used in contrast operation is computed using pixels
                 within the mask. If no mask is given the entire image is used
                 for histogram computation.
    :param preserve_tone: Preserve image tone in Photoshop-like style autocontrast.

                          .. versionadded:: 8.2.0

    :return: An image.
    """
    if preserve_tone:
        histogram = image.convert("L").histogram(mask)
    else:
        histogram = image.histogram(mask)

    lut = []
    for layer in range(0, len(histogram), 256):
        h = histogram[layer : layer + 256]
        if ignore is not None:
            # get rid of outliers
            try:
                h[ignore] = 0
            except TypeError:
                # assume sequence
                for ix in ignore:
                    h[ix] = 0
        if cutoff:
            # cut off pixels from both ends of the histogram
            if not isinstance(cutoff, tuple):
                cutoff = (cutoff, cutoff)
            # get number of pixels
            n = 0
            for ix in range(256):
                n = n + h[ix]
            # remove cutoff% pixels from the low end
            cut = n * cutoff[0] // 100
            for lo in range(256):
                if cut > h[lo]:
                    cut = cut - h[lo]
                    h[lo] = 0
                else:
                    h[lo] -= cut
                    cut = 0
                if cut <= 0: