Python - Circle patter

Question

I would like to create a circle in zeros matrix by changing specific positions from 0 to 1. Unfortunately, something is wrong in my if statement I cannot figure it out. Thanks for helping me!

img = np.zeros((20,20))
def convert2file(image, newfile):
    img = Image.new('RGB', (len(image), len(image[0])), "black")
    pixels = img.load()

    for i in range(len(image)):
        for j in range (len(image[i])):
            if image[i][j] == 0:
                pixels[j,i] = black
            else:
                pixels[j,i] = white


    save2file(img, newfile)
def gen_circle(image):
    ret = np.copy(image)
    for i in range(len(image)):
        for j in range(len(image[i])):
            if fabs((j - len(image)/2)**2 + (i - len(image)/2)**2  - len(image)/2**2) == 0.5**2:
                ret[i][j] = 1
    return ret

draw_pic(gen_circle(img))

Looks like the condition always evaluates `False` and None of the *pixels* get changed to one. You rarely will get two floating point calculations to be equivalent. — wwii, Nov 22 '18 at 01:50
Hard to find the proper image. The expected result is the circle from side to side, top to bottom which is made by 1. The area outside the circle stays 0. — , Nov 22 '18 at 01:51
Are you expecting a circle made with a *line*? Or a filled in disc? — wwii, Nov 22 '18 at 01:55
This part, fabs((j - len(image)/2)**2 + (i - len(image)/2)**2 - len(image)/2**2), never gets the value 0.25. Thus the 'if' statement is never satisfied. — DavidPM, Nov 22 '18 at 01:56

score 0 · Accepted Answer · answered Nov 22 '18 at 02:10

0

How about this code:

def gen_circle(image):
    ret = np.copy(image)
    radius = len(image)/2
    radius_sq = radius**2
    for i in range(len(image)):
        for j in range(len(image[i])):
            if (i-radius)**2 + (j-radius)**2 <= radius_sq:
                ret[i][j] = 1
    return ret

answered Nov 22 '18 at 02:10

John Anderson

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1

`ret[i][j] = 1` --> `ret[i,j] = 1` ... https://docs.scipy.org/doc/numpy/user/basics.indexing.html#single-element-indexing – wwii Nov 22 '18 at 02:12

score -1 · Answer 2 · answered Nov 22 '18 at 02:11

You need to fix the calculation for a couple reasons:

It is very difficult to get an arbitrary calculation to match a floating point value

Almost all of your calculation result in a value that is larger than 0 (some even exceed 100), so most of it will be equal to false

The value of i and j is not balanced (as you started from 0 and end at 19)

You need to select an arbitrary value as the condition (by looking at each of the calculation result, or by trial-and-error) and make the condition to be less than that (to fill the circle up).

import numpy as np
from math import fabs

img = np.zeros((20,20))

def gen_circle(image):
    ret = np.copy(image)
    for i in range(len(image)):
        for j in range(len(image[i])):
            if fabs((j + 0.5 - len(image)/2)**2 + (i + 0.5 - len(image)/2)**2  - len(image)/2**2) <= 86:
                ret[i][j] = 1
    return ret

print(gen_circle(img))

Python - Circle patter

2 Answers2