OpenCV grabcut() background color and Contour in Python

Question

I am using Python and OpenCV. I am now using grabcut() to crop out the object I want. Here is my code:

img = cv2.imread('test.jpg')
img = cv2.cvtColor(img, cv2.COLOR_BGR2RGB)
mask = np.zeros(img.shape[:2], np.uint8)

bgdModel = np.zeros((1, 65), np.float64)
fgdModel = np.zeros((1, 65), np.float64)

rect = (2,2,630,930)
cv2.grabCut(img,mask,rect,bgdModel,fgdModel,5,cv2.GC_INIT_WITH_RECT)

mask2 = np.where((mask==2)|(mask==0), 0,1).astype('uint8')
img = img*mask2[:,:, np.newaxis]

Afterwards, I try to find out the contour.

I have tried to find the contour by the code below:

imgray = cv2.cvtColor(img,cv2.COLOR_BGR2GRAY)
ret,thresh = cv2.threshold(imgray,127,255,0)
im2, contours, hierarchy = cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

And it returns a contours array with length 48. When I draw this out:

First question is how can I get the contour (array) of this grab cut?

Second question: as you can see, the background color is black. How can I change the background color to white?

Thank you.

Answer 1

At first, you need to get the background. To this must be subtracted from the original image with the mask image. And then change the black background to white (or any color). And then back to add with the image of the mask.

import numpy as np
import cv2

cv2.namedWindow(‘image’, cv2.WINDOW_NORMAL)

#Load the Image
imgo = cv2.imread(‘input.jpg’)
height, width = imgo.shape[:2]

#Create a mask holder
mask = np.zeros(imgo.shape[:2],np.uint8)

#Grab Cut the object
bgdModel = np.zeros((1,65),np.float64)
fgdModel = np.zeros((1,65),np.float64)

#Hard Coding the Rect… The object must lie within this rect.
rect = (10,10,width-30,height-30)
cv2.grabCut(imgo,mask,rect,bgdModel,fgdModel,5,cv2.GC_INIT_WITH_RECT)
mask = np.where((mask==2)|(mask==0),0,1).astype(‘uint8’)
img1 = imgo*mask[:,:,np.newaxis]

#Get the background
background = imgo – img1

#Change all pixels in the background that are not black to white
background[np.where((background > [0,0,0]).all(axis = 2))] =[255,255,255]

#Add the background and the image
final = background + img1

#To be done – Smoothening the edges….

cv2.imshow(‘image’, final )

k = cv2.waitKey(0)

if k==27:
cv2.destroyAllWindows()

Information taken from the site https://nxtify.wordpress.com/2015/02/24/image-background-removal-using-opencv-in-python/