In this paper, we propose a method to separately measure the ink dot transmittance on paper without the effect of optical dot gain. The single dot profiles on paper are measured by a monochrome digital camera attached on a microscope using underneath illumination in order to capture only ink dot distribution (mechanical dot gain). From single dot profile on glossy, matt and uncoated paper, the transmittances of the ink image are simulated using dot overlap model in the high resolution grid. The reflectance of ink jet images are estimated from the simulated ink image transmittance and the optical point spread function of paper using the image reflectance model. The result shows that the image transmittance and reflectance are well estimated if the paper behaves as a perfect diffuser.