Extract part of a image using openCV

Question

I'm new to image processing. I wonder if there is any way to extract the star logo from the image?

From only this image? Crop to the relevant coordinates. If you have more than one image, it gets a bit more complicated... I would probably try some sort of Hough line or shape detector, or perhaps template matching on a normalized and otsu local thresholded image. If your dataset is sufficiently massive, you could even try a SOTA object detection model like YOLO. — Mateen Ulhaq, May 02 '21 at 06:43
yes, only from this picture. Can we use Arithmetic and Logic Operations for this? — Pasindu Weerasinghe, May 02 '21 at 06:45
Just measure the coordinates in an image editing program, then do `star_img = img[y1:y2, x1:x2]` — Mateen Ulhaq, May 02 '21 at 06:46

score 4 · Answer 1 · answered May 02 '21 at 06:45

If you want to crop the logo out using OpenCV's cropping tool

import cv2
img = cv2.imread("fight plane.png")
crop_img = img[y:y+h, x:x+w]
cv2.imshow("cropped", crop_img)
cv2.waitKey(0)

Take coordinates. It is extremely easy. There is another question by the topic over here - How to crop an image in OpenCV using Python

score 3 · Accepted Answer · answered May 02 '21 at 07:36

Give this a go

import cv2 as cv
import numpy as np

img = cv.imread('airplane.png')
cv.imshow('Original', img)

blank = np.zeros(img.shape[:2], dtype='uint8')

center_coordinates = (144, 233)

radius = 10

mask = cv.circle(blank, center_coordinates, radius, 255, -1)

masked = cv.bitwise_and(img, img, mask=mask)
cv.imshow('Output', masked)

cv.waitKey(0)

score 1 · Answer 3 · answered May 02 '21 at 07:15

Use cv2.selectROI function

cv2.namedWindow('ROI') 
# define area by mouse
r=cv2.selectROI('ROI', img,False,False)
imROI = img[int(r[1]):int(r[1]+r[3]), int(r[0]):int(r[0]+r[2])]
cv2.destroyWindow('ROI')
cv2.imshow("ROI", imROI)
cv2.waitKey(0)
cv2.destroyAllWindows()

score 0 · Answer 4 · answered May 02 '21 at 06:45

import cv2
import argparse

ref_point = []
crop = False

def shape_selection(event, x, y, flags, param):
    global ref_point, crop

    if event == cv2.EVENT_LBUTTONDOWN:
        ref_point = [(x, y)]
    elif event == cv2.EVENT_LBUTTONUP:
        ref_point.append((x, y))
        cv2.rectangle(image, ref_point[0], ref_point[1], (0, 255, 0), 2)
        cv2.imshow("image", image)


ap = argparse.ArgumentParser()
ap.add_argument("-i", "--image", required = True, help ="Path to the image")
args = vars(ap.parse_args())
image = cv2.imread(args["image"])
clone = image.copy()
cv2.namedWindow("image")
cv2.setMouseCallback("image", shape_selection)
while True:
    cv2.imshow("image", image)
    key = cv2.waitKey(1) & 0xFF
    if key == ord("r"):
        image = clone.copy()
    elif key == ord("c"):
        break
if len(ref_point) == 2:
    crop_img = clone[ref_point[0][1]:ref_point[1][1], ref_point[0][0]:                                                        ref_point[1][0]]
    cv2.imshow("crop_img", crop_img)
    cv2.waitKey(0)
cv2.destroyAllWindows()

try this it will work

Extract part of a image using openCV

4 Answers4