I have trouble in finding the circular grid using the function cv.findCirclesGrid

edit

My link to image is https://drive.google.com/open?id=1Leg.... My code is ++++++++++++++++++++++++++++++++

I=imread('Pattern4.png');
obj = cv.SimpleBlobDetector('MinThreshold',10,'MaxThreshold',255,'ThresholdStep',10,'FilterByColor',true,'BlobColor',255);
keypoints = obj.detect(I2);
im_with_keypoints = cv.drawKeypoints(I2, keypoints,'DrawRichKeypoints',true);
im_with_keypoints_gray = cv.cvtColor(im_with_keypoints,'RGB2GRAY');
imshow(im_with_keypoints) 
[ret,corners] = cv.findCirclesGrid(im_with_keypoints,[2,2]);

+++++++++++++++++++++++++++++

Please tell me why i cannot detect the circular grid?