Porosity analysis using SEM images

[Yusof]

Hi, i am new to the forum. I need help on analysis of porosity in PLGA scaffolds using SEM images. I have surface and cross-sectional images of PLGA scaffold. How do i calculate porosity using Image J? What are the steps? Please do help, thanks

[Yusof]

This is the image of surfacemview

https://www.dropbox.com/s/5x982ypzqgx10ja/plga-cs-50x051104.bmp?dl=0

This is the image of crosssectional view

https://www.dropbox.com/s/u492tv203nkbbwy/plga400-front-22-8-1.jpg?dl=0

How do i calculate porosity using Image J? What are the steps? Please do help, thanks