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148 lines
3.8 KiB
Python
148 lines
3.8 KiB
Python
#
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# The Python Imaging Library.
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# $Id$
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#
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# global image statistics
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#
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# History:
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# 1996-04-05 fl Created
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# 1997-05-21 fl Added mask; added rms, var, stddev attributes
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# 1997-08-05 fl Added median
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# 1998-07-05 hk Fixed integer overflow error
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#
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# Notes:
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# This class shows how to implement delayed evaluation of attributes.
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# To get a certain value, simply access the corresponding attribute.
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# The __getattr__ dispatcher takes care of the rest.
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#
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# Copyright (c) Secret Labs AB 1997.
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# Copyright (c) Fredrik Lundh 1996-97.
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#
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# See the README file for information on usage and redistribution.
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#
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import functools
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import math
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import operator
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class Stat:
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def __init__(self, image_or_list, mask=None):
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try:
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if mask:
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self.h = image_or_list.histogram(mask)
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else:
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self.h = image_or_list.histogram()
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except AttributeError:
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self.h = image_or_list # assume it to be a histogram list
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if not isinstance(self.h, list):
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raise TypeError("first argument must be image or list")
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self.bands = list(range(len(self.h) // 256))
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def __getattr__(self, id):
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"""Calculate missing attribute"""
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if id[:4] == "_get":
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raise AttributeError(id)
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# calculate missing attribute
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v = getattr(self, "_get" + id)()
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setattr(self, id, v)
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return v
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def _getextrema(self):
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"""Get min/max values for each band in the image"""
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def minmax(histogram):
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n = 255
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x = 0
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for i in range(256):
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if histogram[i]:
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n = min(n, i)
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x = max(x, i)
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return n, x # returns (255, 0) if there's no data in the histogram
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v = []
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for i in range(0, len(self.h), 256):
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v.append(minmax(self.h[i:]))
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return v
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def _getcount(self):
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"""Get total number of pixels in each layer"""
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v = []
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for i in range(0, len(self.h), 256):
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v.append(functools.reduce(operator.add, self.h[i : i + 256]))
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return v
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def _getsum(self):
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"""Get sum of all pixels in each layer"""
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v = []
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for i in range(0, len(self.h), 256):
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layer_sum = 0.0
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for j in range(256):
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layer_sum += j * self.h[i + j]
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v.append(layer_sum)
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return v
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def _getsum2(self):
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"""Get squared sum of all pixels in each layer"""
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v = []
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for i in range(0, len(self.h), 256):
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sum2 = 0.0
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for j in range(256):
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sum2 += (j**2) * float(self.h[i + j])
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v.append(sum2)
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return v
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def _getmean(self):
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"""Get average pixel level for each layer"""
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v = []
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for i in self.bands:
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v.append(self.sum[i] / self.count[i])
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return v
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def _getmedian(self):
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"""Get median pixel level for each layer"""
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v = []
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for i in self.bands:
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s = 0
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half = self.count[i] // 2
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b = i * 256
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for j in range(256):
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s = s + self.h[b + j]
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if s > half:
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break
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v.append(j)
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return v
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def _getrms(self):
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"""Get RMS for each layer"""
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v = []
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for i in self.bands:
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v.append(math.sqrt(self.sum2[i] / self.count[i]))
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return v
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def _getvar(self):
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"""Get variance for each layer"""
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v = []
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for i in self.bands:
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n = self.count[i]
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v.append((self.sum2[i] - (self.sum[i] ** 2.0) / n) / n)
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return v
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def _getstddev(self):
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"""Get standard deviation for each layer"""
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v = []
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for i in self.bands:
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v.append(math.sqrt(self.var[i]))
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return v
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Global = Stat # compatibility
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