The high-resolution SEM micrographs were image-processed to analyze the porosity of the coated CNT membrane. Both pristine and CNTs with B4C films of various thicknesses were studied for comparison. The working distance, accelerating voltage, aperture, magnifications, brightness, and contrast of the micrographs were kept constant among the processed micrographs. A magnification of 100 000-times was determined to be optimum for minimizing the position independent deviation from the average statistical distribution of the membrane features. Initially, the images were converted to gray scale and the contrasts of the images were normalized by linearly mapping the intensity values from 0 to 255. The number of depth levels were identified by analyzing the peaks in the histograms of the images. The pore distribution was mapped by processing the binarized micrographs using gradient magnitude, followed by watershed algorithms in Matlab, see the supporting information for details. The porosity was estimated by averaging the pixel intensity values of the gray scale depth mapped micrographs and expressed in 0 to 1 scale.