NIH Image, freeware for Macintosh computers, is used to obtain quantitative porosity values from digitized images of thin sections. The digital images are modified to reduce contrast and give the pores, or feature of interest, a unique color. NIH Image is used to measure the number of pixels of each color in the pore space and the total number of pixels in the image. This technique can be used for quantitative assessment of any digital image.

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