| # | |
| # 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: | |