1. A method for printing on transparent medium using an ink-jet printer, comprising: providing a grayscale image having a plurality of pixels, each pixel having a pixel value corresponding to a brightness of the pixel; and converting each pixel value to an ink output value for the ink-jet printer using a conversion function, wherein the conversion function maps the darkest pixel value to an optical density of greater than 2.5 and maps all other pixel values to an appropriate output pixel value such that a resulting printed image is perceived to be linearly bright across the image.