Source code for PIL.ImageStat

#
# 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.
#

import functools
import math
import operator


[docs]class Stat: def __init__(self, image_or_list, mask=None): try: if mask: self.h = image_or_list.histogram(mask) else: self.h = image_or_list.histogram() except AttributeError: self.h = image_or_list # assume it to be a histogram list if not isinstance(self.h, list): raise TypeError("first argument must be image or list") self.bands = list(range(len(self.h) // 256)) def __getattr__(self, id): """Calculate missing attribute""" if id[:4] == "_get": raise AttributeError(id) # calculate missing attribute v = getattr(self, "_get" + id)() setattr(self, id, v) return v def _getextrema(self): """Get min/max values for each band in the image""" def minmax(histogram): n = 255 x = 0 for i in range(256): if histogram[i]: n = min(n, i) x = max(x, i) return n, x # returns (255, 0) if there's no data in the histogram v = [] for i in range(0, len(self.h), 256): v.append(minmax(self.h[i:])) return v def _getcount(self): """Get total number of pixels in each layer""" v = [] for i in range(0, len(self.h), 256): v.append(functools.reduce(operator.add, self.h[i : i + 256])) return v def _getsum(self): """Get sum of all pixels in each layer""" v = [] for i in range(0, len(self.h), 256): layerSum = 0.0 for j in range(256): layerSum += j * self.h[i + j] v.append(layerSum) return v def _getsum2(self): """Get squared sum of all pixels in each layer""" 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 def _getmean(self): """Get average pixel level for each layer""" v = [] for i in self.bands: v.append(self.sum[i] / self.count[i]) return v def _getmedian(self): """Get median pixel level for each layer""" 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 def _getrms(self): """Get RMS for each layer""" v = [] for i in self.bands: v.append(math.sqrt(self.sum2[i] / self.count[i])) return v def _getvar(self): """Get variance for each layer""" v = [] for i in self.bands: n = self.count[i] v.append((self.sum2[i] - (self.sum[i] ** 2.0) / n) / n) return v def _getstddev(self): """Get standard deviation for each layer""" v = [] for i in self.bands: v.append(math.sqrt(self.var[i])) return v
Global = Stat # compatibility