Hello Rahman, Try like this once

Apply adaptive thresholding on the gray level image.

Find distance transform on the thresholded image.

Invert the distance transform and assign a high value to the background.

Extract marker using gray scale reconstruction and assign zero value to marker.

Apply watershed transformation on the marker embedded inverted distance image to obtain the segmented image.

Use gray scale reconstruction to find radius of each droplet and subsequently calculate area of each labelled droplet.

Hi Irawan,

Thanks for your comment.

By the way, it's not about Photoshop. PSD is the atmospheric aerosol's number size distribution measured by SMPS instrument. I am talking about plotting of the SMPS instrument's data using R commands.

Rahman

I recently wrote some R code for something like this, you can see it here: http://stackoverflow.com/questions/36014676/use-r-to-recreate-contour-plot-made-in-igor and in a github gist here: https://gist.github.com/benmarwick/9a54cbd325149a8ff405