Python: Opencv - Selecting Region of an Image

Python: OpenCV - Selecting Region of an Image

You are correct about the ROI-Formular which is [y:y+h, x:x+w], however the initial point on y coordinate is wrong that is why you are cropping the white region of the image.

You are probably looking for:

dmc = im[13:13+287, 938:938+287]
cv2.imshow('dmc', dmc)

Result:

OpenCV: return only selected area of an image and return the rest as black

The issue has been solved by creating masks and combine the foreground and background by these lines of code:

import cv2
import numpy as np

pic= cv2.imread('Assets/set.jpeg')
pic = cv2.resize(pic, dsize=(500, 400), interpolation=cv2.INTER_CUBIC)
gray=cv2.cvtColor(pic,cv2.COLOR_BGR2GRAY)
blur = cv2.GaussianBlur(gray,(5,5),5)
_,thres = cv2.threshold(blur, 100,250, cv2.THRESH_TOZERO)
res = cv2.Canny(thres, 100, 250, L2gradient=True)

circles = cv2.HoughCircles(res,cv2.HOUGH_GRADIENT,1,20,param1=200,param2=15,minRadius=80,maxRadius=100)
circles = np.uint16(np.around(circles))

mask = np.full((res.shape[0], res.shape[1]), 1, dtype=np.uint8)  # mask is only 
clone = pic.copy()
for i in circles[0, :]:
    cv2.circle(mask, (i[0], i[1]), i[2], (255, 255, 255), -1)
    cv2.circle(clone, (i[0], i[1]), i[2], (255, 255, 255), 1)

# get first masked value (foreground)
fg = cv2.bitwise_or(res, res, mask=mask)

# get second masked value (background) mask must be inverted
mask = cv2.bitwise_not(mask)
background = np.full(res.shape, 255, dtype=np.uint8)
bk = cv2.bitwise_or(background, background, mask=mask)

# combine foreground+background
final = cv2.bitwise_or(fg, bk)

result = np.concatenate((res,final),axis=1)
cv2.imshow('Hole',result)
cv2.waitKey(0)
cv2.destroyAllWindows()

Nothing to be asked anymore and I will close the question. Thank you!!

How to select region on image and extract pixel values in numbers of that particular region?

The function to use is cv.selectROI

It can take different arguments. The simplest case is just taking an image (numpy array). Here's an example where also the window name is specified.

Personally I also prefer to use the fromCenter argument.

import numpy as np
import cv2 as cv

im = cv.imread(cv.samples.findFile("lena.jpg"))

bbox = cv.selectROI("lena", im, fromCenter=True)
cv.destroyWindow("lena")

print("region:", bbox)

(x,y,w,h) = bbox

subregion = im[y:y+h, x:x+w]
cv.imshow("lena subregion", subregion)
cv.waitKey(-1)
cv.destroyWindow("lena subregion")

How to extract ID document region of interest from image with OpenCV?

You're almost there, you just need to obtain the x,y,w,h bounding rectangle coordinates using cv2.boundingRect then you can extract/save the ROI using Numpy slicing. Here's the result

import cv2

# Load image, grayscale, threshold
image = cv2.imread('1.jpg')
gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
blur = cv2.GaussianBlur(gray, (3,3), 0)
thresh = cv2.threshold(gray, 225, 255, cv2.THRESH_BINARY_INV)[1]

# Get bounding box and extract ROI
x,y,w,h = cv2.boundingRect(thresh)
ROI = image[y:y+h, x:x+w]

cv2.imshow('thresh', thresh)
cv2.imshow('ROI', ROI)
cv2.waitKey()

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