Hello Mojtaba, you have to first convert the image into black and whtie using the inbuilt function in matlab "im2bw", you will then get your desired second image. Regarding the area, the total area occupied by all the white regions in image 2 can be computed using the function "bwarea", whereas for computing individual areas, you will have to use image segmentation. One such example is given in:

https://in.mathworks.com/matlabcentral/answers/154484-how-can-i-calculate-area-of-an-object-in-the-image-with-png-extension

and 

https://in.mathworks.com/help/images/examples/detect-and-measure-circular-objects-in-an-image.html

sohaib your input is appealing me.