chapter8.py

import cv2
import numpy as np

#           Contours / shape detection

def stackImages(scale,imgArray):        # function for stacking images
    rows = len(imgArray)
    cols = len(imgArray[0])
    rowsAvailable = isinstance(imgArray[0], list)
    width = imgArray[0][0].shape[1]
    height = imgArray[0][0].shape[0]
    if rowsAvailable:
        for x in range ( 0, rows):
            for y in range(0, cols):
                if imgArray[x][y].shape[:2] == imgArray[0][0].shape [:2]:
                    imgArray[x][y] = cv2.resize(imgArray[x][y], (0, 0), None, scale, scale)
                else:
                    imgArray[x][y] = cv2.resize(imgArray[x][y], (imgArray[0][0].shape[1], imgArray[0][0].shape[0]), None, scale, scale)
                if len(imgArray[x][y].shape) == 2: imgArray[x][y]= cv2.cvtColor( imgArray[x][y], cv2.COLOR_GRAY2BGR)
        imageBlank = np.zeros((height, width, 3), np.uint8)
        hor = [imageBlank]*rows
        # hor_con = [imageBlank]*rows
        for x in range(0, rows):
            hor[x] = np.hstack(imgArray[x])
        ver = np.vstack(hor)
    else:
        for x in range(0, rows):
            if imgArray[x].shape[:2] == imgArray[0].shape[:2]:
                imgArray[x] = cv2.resize(imgArray[x], (0, 0), None, scale, scale)
            else:
                imgArray[x] = cv2.resize(imgArray[x], (imgArray[0].shape[1], imgArray[0].shape[0]), None,scale, scale)
            if len(imgArray[x].shape) == 2: imgArray[x] = cv2.cvtColor(imgArray[x], cv2.COLOR_GRAY2BGR)
        hor= np.hstack(imgArray)
        ver = hor
    return ver


def getContours(img):   # this function draws the contour i.e. detects the shapes and draw the border around it
    contours, hierarchy = cv2.findContours(img, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)   # returns the list of contours
    for cnt in contours:
        area = cv2.contourArea(cnt)     # returns the area of the contour passed as a parameter
        print(area)
        if area > 500:
            cv2.drawContours(imgContour, cnt, -1, (255, 0, 0), 3)  # draws the border around the contour on the image passed. image, contour, index of contour(-1 to consider all the contour), color of the border which is gonna be drawn, width of the border


img = cv2.imread('resources/shapes.png')
imgContour = img.copy()     # making copy of the image

imgGray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
imgBlur = cv2.GaussianBlur(imgGray, (7, 7), 1)
imgCanny = cv2.Canny(imgBlur, 50, 50)
imgBlank = np.zeros_like(img)

getContours(imgCanny)
imgStack = stackImages(0.6, ([img, imgGray, imgBlur],
                             [imgCanny, imgContour, imgBlank]))
cv2.imshow('stack', imgStack)
cv2.waitKey(0)