CODEWITHSUNDEEP
pythonruntime-errorlogarithm
svacx
svacx

Reputation: 69

ValueError: math domain error (python)

I was testing the math module and PIL module, and trying to apply a box count algorithm on a Image. When I run that code below I get the following error:

Traceback (most recent call last):
  File "C:\Users\Joao\Desktop\Image Size.py", line 48, in <module>
    gy.append(math.log(boxCount))
ValueError: math domain error

Code:

import Tkinter as tk
from Tkinter import *
from PIL import Image, ImageTk
import os, glob, tkFileDialog
import math


im = Image.open("img1.bmp")
width, height = im.size
print width
print height

imgx = width
imgy = height

pixels = im.load()
theColor = (255, 255, 255)


# fractal dimension calculation using box-counting method
b = 2 # initial box size in pixels
f = 2 # box scaling factor
n = 3 # number of graph points for simple linear regression
gx = [] # x coordinates of graph points
gy = [] # y coordinates of graph points
for ib in range(n):
    bs = b * f ** ib # box size in pixels
    bnx = int(imgx / bs) # of boxes in x direction of image
    bny = int(imgy / bs) # of boxes in y direction of image
    boxCount = 0
    for by in range(bny):
        for bx in range(bnx):
        # if there are any pixels in the box then increase box count
            foundPixel = False
            for ky in range(bs):
                for kx in range(bs):
                    if pixels[bs * bx + kx, bs * by + ky] == theColor:
                        foundPixel = True
                        boxCount += 1
                        break
                if foundPixel:
                    break
    gx.append(math.log(1.0 / bs))
    gy.append(math.log(boxCount))

I found that if I change the value of boxcount to 1 (instead of zero) it produces no error at all, but I need the boxcount value to be 0. Can anyone suggest a solution?

Upvotes: 4

Views: 12656

Answers (1)

Irshad Bhat
Irshad Bhat

Reputation: 8709

Since log of negative or zero is not defined.So replace :

gy.append(math.log(boxCount))

with this :

gy.append(math.log(boxCount if boxCount>0 else 1))

Upvotes: 5

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