Gray scale Image Processing of a composite structure

Hello, I have a gray-scale image of a composite structure consisting of grains,grain boundaries and particles embedded in the grains.The problem is that the grain boundaries and the small embedded particles are white in color and the rest of the image is black.How should i distinguish between the particle and the grain boundary if both of them are black in color? Thanks.

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/7924-where-can-i-upload-images-and-files-for-use-on-matlab-answers

Answer 1

[Image Analyst]

You'd probably have to use an edge detector and then threshold that to get the grains. That assumes that they are not all completely black and the same intensity. Obviously if your whole image has value 0, you can't see anything. Please upload an image.