How can I extract all regions from an image? - python-2.7

Question

I have an image like below. Dimension of the image is fixed: 640x480.
I want to bound all non-zero regions with rectangles like this:
I need to know the upper-right, and lower-left points of each of these rectangles.
I have thought about loops and other methods. But all of them will take too long to run. What is the most efficient way to do this in python?
PS: I am a beginner in image processing. This might be an obvious question, i don't know. So giving me a sample code would help a lot. Thanks.

Answer 1

Finding all sub-components within an image is called connected component analysis. In OpenCV you can do it with findCountour() function of its contour analysis library.
Here is a sample code:
import cv2
import numpy as np
from scipy import signal
#=========================================================================
# Locate all components
#=========================================================================
def locateComponents(img):
"""Extracts all components from an image"""
out = img.copy()
res = cv2.findContours(np.uint8(out.copy()),\
cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
contours = res[1]
ret = []
row, col = out.shape
minSiz = 8
for cnt in contours:
# get bounding box
y, x, n, m = cv2.boundingRect(cnt)
# check area
if m < minSiz or n < minSiz:
continue
#end if
ret.append(np.int32([x, x+m, y, y+n]))
out = cv2.rectangle(out, (y,x), (y+n,x+m), (255,255,255), 2)
#end for
return ret, out
# end function
#=========================================================================
# TESTING
#=========================================================================
img = cv2.imread('input.jpg', 0)
regions, out = locateComponents(img)
cv2.imwrite('output.jpg', out)
print regions
cv2.imshow('Given image', img)
cv2.imshow('Located regions', out)
cv2.waitKey(0)
The output image: