Opitcal images thresholding issue

[Kj101114.]

Hello,

I have some images obtained using optical microscopy - my final aim will be to measure the total porosity of the samples (which I believe I know how to do) the issue is that I cant apply the threshold correctly in order for all obvious pores(grey) to be accounted for - it just starts picking up the whole of the image including the solid phase (brown)




Is there a way I can manipulate the images prior to analysis so that the difference between the solid phase and pore space can be distinguished more - so that I can apply the threshold successfully

I do have so florescent images - however, these are not great quality and obviously eliminate closed porosity, which is of particular importance in this research.


Any ideas?

Thanks in advance,
Katie