A simple and easy method for the simultaneous monitoring of colony shape and ammonia productivity of swarming bacteria such as Proteus mirabilis should become increasingly important for the characterization of the bacteria. A contactless mapping method of ammonia concentration produced by Proteus mirabilis colony is proposed using an array of pH indicator solution and a digital still camera, by using a PC display as a backlight. Brightness of the indicator solution was quantified from the captured image using image processing software. At the same time, fine structures in the colony were observed due to the diffraction of the display's transmitted light pattern. In 5 min, the ammonia productivity difference from different concentric circles was identified. Bacteria cell density of different regions of the concentric colony pattern on the agar surface was measured, and the effect of the density on the ammonia productivity was discussed.