ContoursEllipses.py

import numpy as np
import cv2
from matplotlib import pyplot as plt

def Roundness(contour, moments):
    length = cv2.arcLength(contour, True)
    k = (length * length) / (moments['m00'] * 4 * np.pi)
    return k

def GetPositionToDraw(text, point, font_face, font_scale, thickness):
    text_size = cv2.getTextSize(text, font_face, font_scale, thickness)[0]
    text_x = point[0] - text_size[0] / 2
    text_y = point[1] + text_size[1] / 2
    return round(text_x), round(text_y)

def EccentricityFromEllipse(contour):
    (x, y), (MA, ma), angle = cv2.fitEllipse(contour)
    a = ma / 2
    b = MA / 2
    ecc = np.sqrt(a ** 2 - b ** 2) / a
    return ecc

def EccentricityFromMoments(moments):
    a1 = (moments['mu20'] + moments['mu02']) / 2
    a2 = np.sqrt(4 * moments['mu11'] ** 2 + (moments['mu20'] - moments['mu02']) ** 2) / 2
    ecc = np.sqrt(1 - (a1 - a2) / (a1 + a2))
    return ecc

def BuildImageEllipses():
    img = np.zeros((500, 600, 3), dtype="uint8")
    cv2.ellipse(img, (120, 60), (100, 50), 0, 0, 360, (255, 255, 0), -1)
    cv2.ellipse(img, (300, 60), (50, 50), 0, 0, 360, (0, 0, 255), -1)
    cv2.ellipse(img, (425, 200), (50, 150), 0, 0, 360, (255, 0, 0), -1)
    cv2.ellipse(img, (550, 250), (20, 240), 0, 0, 360, (255, 0, 255), -1)
    cv2.ellipse(img, (200, 200), (150, 50), 0, 0, 360, (0, 255, 0), -1)
    cv2.ellipse(img, (250, 400), (200, 50), 0, 0, 360, (0, 255, 255), -1)
    return img

def DrawContourOutline(img, cnts, color, thickness=1):
    for cnt in cnts:
        cv2.drawContours(img, [cnt], 0, color, thickness)

def ShowImgWithMatplotlib(colorImg, title, pos):
    imgRGB = colorImg[:, :, ::-1]
    ax = plt.subplot(1, 2, pos)
    plt.imshow(imgRGB)
    plt.title(title)
    plt.axis('off')

fig = plt.figure(figsize=(14, 6))
plt.suptitle("Eccentricity", fontsize=14, fontweight='bold')
fig.patch.set_facecolor('silver')

image = BuildImageEllipses()
grayImage = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
ret, thresh = cv2.threshold(grayImage, 20, 255, cv2.THRESH_BINARY)
contours, hierarchy = cv2.findContours(thresh, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)
print("detected contours: '{}' ".format(len(contours)))

imgNumbers = image.copy()
for contour in contours:
    DrawContourOutline(image, [contour], (255, 255, 255), 5)
    M = cv2.moments(contour)
    k = Roundness(contour, M)
    print("roundness: '{}'".format(k))

    em = EccentricityFromMoments(M)
    print("eccentricity: '{}'".format(em))
    ee = EccentricityFromEllipse(contour)
    print("eccentricity: '{}'".format(ee))

    cX = int(M['m10'] / M['m00'])
    cY = int(M['m01'] / M['m00'])
    textToDraw = str(round(em, 3))
    (x, y) = GetPositionToDraw(textToDraw, (cX, cY), cv2.FONT_HERSHEY_SIMPLEX, 1, 3)
    cv2.putText(imgNumbers, textToDraw, (x, y), cv2.FONT_HERSHEY_SIMPLEX, 1, (255, 255, 255), 3)

ShowImgWithMatplotlib(image, "image", 1)
ShowImgWithMatplotlib(imgNumbers, "ellipses eccentricity", 2)

plt.show()