Detect bright white blob on Grey/light white Background - image-processing

I am new to OpenCV and I have this project where I need to detect brighter white color blobs on grey background. Could someone help me with some possible solution, ideally with OpenCV?
Original Image:
Blobs to be detected:

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Converting it into grayscale and then reading it
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Much appreciate your help in solving this.
Cheers
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However, there exists a tricky solution. You may first refer to this question to create a mask of your floodfill area. Then you can easily calculate the alpha channel from this mask.

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