OpenCV python overlapping particles size and number

I got greyscale images which show particles on a surface. I like to write a program which finds the particles draws a circle around and gives counts the circles and the pixels inside the circles. One of the main problems is that the particles overlapp. The next problem is that the contrast of the images is changing, from one image to the next. Here is my first trial:

import matplotlib.pyplot as plt
import cv2 as cv
import imutils
import numpy as np
import matplotlib.pyplot as plt
from PIL import Image
import os.path

fileref="test.png"
original = cv.imread(fileref)
img = original
cv.imwrite( os.path.join("inverse_"+fileref[:-4]+".png"), ~img );

img = cv.medianBlur(img,5)
img_grey = cv.cvtColor(img, cv.COLOR_BGR2GRAY)

ret,th1 = cv.threshold(img_grey,130,255,cv.THRESH_BINARY)
th2 = cv.adaptiveThreshold(img_grey,255,cv.ADAPTIVE_THRESH_MEAN_C,\
            cv.THRESH_BINARY,11,2)
th3 = cv.adaptiveThreshold(img_grey,255,cv.ADAPTIVE_THRESH_GAUSSIAN_C,\
            cv.THRESH_BINARY,11,2)

titles = ['Original Image', 'Global Thresholding (v = 127)',
            'Adaptive Mean Thresholding', 'Adaptive Gaussian Thresholding']
images = [img, th1]

cv.imwrite( os.path.join("threshhold_"+fileref[:-4]+".jpg"), th1 );
cv.imwrite( os.path.join("adaptivthreshhold-m_"+fileref[:-4]+".jpg"), th2 );
cv.imwrite( os.path.join("adaptivthreshhold-g_"+fileref[:-4]+".jpg"), th3 );


imghsv = cv.cvtColor(img, cv.COLOR_BGR2HSV)


imghsv[:,:,2] = [[max(pixel - 25, 0) if pixel < 190 else min(pixel + 25, 255) for pixel in row] for row in imghsv[:,:,2]]
cv.imshow('contrast', cv.cvtColor(imghsv, cv.COLOR_HSV2BGR))

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

# Change thresholds
params.minThreshold = 0
params.maxThreshold = 150


# Filter by Convexity
params.filterByConvexity = True
params.minConvexity = 0.87

# Filter by Inertia
params.filterByInertia = True
params.minInertiaRatio = 0.08 # 0.08
# Set edge gradient
params.thresholdStep = 0.5

# Filter by Area.
params.filterByArea = True
params.minArea = 300

# Set up the detector with default parameters.
detector = cv.SimpleBlobDetector_create(params)

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

# 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 = cv.drawKeypoints(original, keypoints, np.array([]), (0, 0, 255),
                                      cv.DRAW_MATCHES_FLAGS_DRAW_RICH_KEYPOINTS)
print(len(keypoints))
# Show keypoints
display=cv.resize(im_with_keypoints,None,fx=0.5,fy=0.5)
cv.imshow("Keypoints", display)
cv.waitKey(0)
cv.imwrite( os.path.join("keypoints_"+fileref[:-4]+".jpg"), im_with_keypoints );

It circles most particles but the parameters need to be changed for each image to get better results the circles can't overlapp and I don't know how to count the circles or count the pixels inside the circles. Any help or hints which point me in the right direction are much appreciated. I added a couple sample pics

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