simple blob Detection

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Hi, I am trying to detect simple blobs in an image but while running code, I get the image without any keypoints plotted. Why am I not able to detect the blobs?

import cv2
import numpy as np;
im = cv2.imread('blob1.jpeg', cv2.IMREAD_GRAYSCALE)

# Setup SimpleBlobDetector parameters.
params = cv2.SimpleBlobDetector_Params()

# Change thresholds
params.minThreshold = 50
params.maxThreshold = 150
# Filter by Area.
params.filterByArea = True
params.minArea = 150
detector = cv2.SimpleBlobDetector_create(params)

# Detect blobs.
keypoints = detector.detect(im)

# Draw detected blobs as red circles.
# cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS ensures
# the size of the circle corresponds to the size of blob

im_with_keypoints = cv2.drawKeypoints(im, keypoints, np.array([]), (255,0,0), cv2.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)

# Show blobs
cv2.imshow("Keypoints", im_with_keypoints)
cv2.waitKey(0)
cv2.destroyAllWindows()