Described is a technology for measuring ink film thickness by use of differential lighting between two differently positioned light sources. The technology involves an image capture device, a first set of light emitting diodes (LEDs), and a second set of LEDs, where the image capture device is attached to a printer. The first set of LEDs is positioned in parallel to an image capture axis to illuminate a target object evenly from above with a light perpendicular to the target object (e.g., substrate with deposited ink droplets). The second set of LEDs is positioned to illuminate the target object at an angle, thereby casting a shadow. The image capture device takes two snapshots of the target object, utilizing a different light source (of the two sets of LEDs) for each snapshot. The snapshots are compared to determine the shadow's magnitude and the ink film thickness based on the shadow.