CODEWITHSUNDEEP
pythonopencv
Liana Olianov
Liana Olianov

Reputation: 65

Drawing SIFT keypoints

I am using a SIFT keypoint extractor/descriptor to extract and plot keypoints on an image as shown in the code below:

import cv2 as cv 
img = cv.imread("my_img.jpg")
sift = cv.SIFT_create()
(keypoints, descriptors) = sift.detectAndCompute(img,None)
img_kp=cv.drawKeypoints(img,kp,cv.DRAW_MATCHES_FLAGS_DEFAULT,color=(120,157,187))
cv.imwrite("img.jpg", img_kp)

the code above draw keypoints as orange circles, how can I change the representation to an orange "+" sign for each keypoint ?

Thank you very much for your help

Upvotes: 2

Views: 1973

Answers (1)

Rotem
Rotem

Reputation: 32094

A simple solution may be: Iterating all keypoints and draw a "+" sign using cv2.drawMarker.

Here is a code sample:

import numpy as np
import cv2


def draw_cross_keypoints(img, keypoints, color):
    """ Draw keypoints as crosses, and return the new image with the crosses. """
    img_kp = img.copy()  # Create a copy of img

    # Iterate over all keypoints and draw a cross on evey point.
    for kp in keypoints:
        x, y = kp.pt  # Each keypoint as an x, y tuple  https://stackoverflow.com/questions/35884409/how-to-extract-x-y-coordinates-from-opencv-cv2-keypoint-object

        x = int(round(x))  # Round an cast to int
        y = int(round(y))

        # Draw a cross with (x, y) center
        cv2.drawMarker(img_kp, (x, y), color, markerType=cv2.MARKER_CROSS, markerSize=5, thickness=1, line_type=cv2.LINE_8)

    return img_kp  # Return the image with the drawn crosses.


img = cv2.imread("my_img.jpg")
sift = cv2.SIFT_create()
(keypoints, descriptors) = sift.detectAndCompute(img, None)
#img_kp = cv2.drawKeypoints(img, keypoints, cv2.DRAW_MATCHES_FLAGS_DEFAULT, color=(120,157,187))
img_kp = draw_cross_keypoints(img, keypoints, color=(120,157,187))  # Draw keypoints as "+" signs
cv2.imwrite("img.jpg", img_kp)

Sample result:
enter image description here

Crosses and circles - for testing:
enter image description here

As you can see, the "+" sings are at the centers of the circles.

Upvotes: 3

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