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+#
+# The Python Imaging Library.
+# $Id$
+#
+# global image statistics
+#
+# History:
+# 1996-04-05 fl Created
+# 1997-05-21 fl Added mask; added rms, var, stddev attributes
+# 1997-08-05 fl Added median
+# 1998-07-05 hk Fixed integer overflow error
+#
+# Notes:
+# This class shows how to implement delayed evaluation of attributes.
+# To get a certain value, simply access the corresponding attribute.
+# The __getattr__ dispatcher takes care of the rest.
+#
+# Copyright (c) Secret Labs AB 1997.
+# Copyright (c) Fredrik Lundh 1996-97.
+#
+# See the README file for information on usage and redistribution.
+#
+from __future__ import annotations
+
+import math
+from functools import cached_property
+
+from . import Image
+
+
+class Stat:
+ def __init__(
+ self, image_or_list: Image.Image | list[int], mask: Image.Image | None = None
+ ) -> None:
+ """
+ Calculate statistics for the given image. If a mask is included,
+ only the regions covered by that mask are included in the
+ statistics. You can also pass in a previously calculated histogram.
+
+ :param image: A PIL image, or a precalculated histogram.
+
+ .. note::
+
+ For a PIL image, calculations rely on the
+ :py:meth:`~PIL.Image.Image.histogram` method. The pixel counts are
+ grouped into 256 bins, even if the image has more than 8 bits per
+ channel. So ``I`` and ``F`` mode images have a maximum ``mean``,
+ ``median`` and ``rms`` of 255, and cannot have an ``extrema`` maximum
+ of more than 255.
+
+ :param mask: An optional mask.
+ """
+ if isinstance(image_or_list, Image.Image):
+ self.h = image_or_list.histogram(mask)
+ elif isinstance(image_or_list, list):
+ self.h = image_or_list
+ else:
+ msg = "first argument must be image or list" # type: ignore[unreachable]
+ raise TypeError(msg)
+ self.bands = list(range(len(self.h) // 256))
+
+ @cached_property
+ def extrema(self) -> list[tuple[int, int]]:
+ """
+ Min/max values for each band in the image.
+
+ .. note::
+ This relies on the :py:meth:`~PIL.Image.Image.histogram` method, and
+ simply returns the low and high bins used. This is correct for
+ images with 8 bits per channel, but fails for other modes such as
+ ``I`` or ``F``. Instead, use :py:meth:`~PIL.Image.Image.getextrema` to
+ return per-band extrema for the image. This is more correct and
+ efficient because, for non-8-bit modes, the histogram method uses
+ :py:meth:`~PIL.Image.Image.getextrema` to determine the bins used.
+ """
+
+ def minmax(histogram: list[int]) -> tuple[int, int]:
+ res_min, res_max = 255, 0
+ for i in range(256):
+ if histogram[i]:
+ res_min = i
+ break
+ for i in range(255, -1, -1):
+ if histogram[i]:
+ res_max = i
+ break
+ return res_min, res_max
+
+ return [minmax(self.h[i:]) for i in range(0, len(self.h), 256)]
+
+ @cached_property
+ def count(self) -> list[int]:
+ """Total number of pixels for each band in the image."""
+ return [sum(self.h[i : i + 256]) for i in range(0, len(self.h), 256)]
+
+ @cached_property
+ def sum(self) -> list[float]:
+ """Sum of all pixels for each band in the image."""
+
+ v = []
+ for i in range(0, len(self.h), 256):
+ layer_sum = 0.0
+ for j in range(256):
+ layer_sum += j * self.h[i + j]
+ v.append(layer_sum)
+ return v
+
+ @cached_property
+ def sum2(self) -> list[float]:
+ """Squared sum of all pixels for each band in the image."""
+
+ v = []
+ for i in range(0, len(self.h), 256):
+ sum2 = 0.0
+ for j in range(256):
+ sum2 += (j**2) * float(self.h[i + j])
+ v.append(sum2)
+ return v
+
+ @cached_property
+ def mean(self) -> list[float]:
+ """Average (arithmetic mean) pixel level for each band in the image."""
+ return [self.sum[i] / self.count[i] for i in self.bands]
+
+ @cached_property
+ def median(self) -> list[int]:
+ """Median pixel level for each band in the image."""
+
+ v = []
+ for i in self.bands:
+ s = 0
+ half = self.count[i] // 2
+ b = i * 256
+ for j in range(256):
+ s = s + self.h[b + j]
+ if s > half:
+ break
+ v.append(j)
+ return v
+
+ @cached_property
+ def rms(self) -> list[float]:
+ """RMS (root-mean-square) for each band in the image."""
+ return [math.sqrt(self.sum2[i] / self.count[i]) for i in self.bands]
+
+ @cached_property
+ def var(self) -> list[float]:
+ """Variance for each band in the image."""
+ return [
+ (self.sum2[i] - (self.sum[i] ** 2.0) / self.count[i]) / self.count[i]
+ for i in self.bands
+ ]
+
+ @cached_property
+ def stddev(self) -> list[float]:
+ """Standard deviation for each band in the image."""
+ return [math.sqrt(self.var[i]) for i in self.bands]
+
+
+Global = Stat # compatibility