A CMOS image sensor with light intensity filtering feature for realizing image thresholding is proposed. The simple sensing pixel circuit with less than 5 transistors is designed to provide a tunable non-linear photo-response with a peak signal at a specified intensity level. This unique intensity-filtering photo-response characteristic is achieved by the push/pull forces between the n+/p photo-diode and a parasitic p+/n-well diode on the PMOS control transistor. With proper timing control, tunable intensity filtering transfer functions can be obtained on the unique pixel. Based on the behavior model of the pixel's photo-response, image thresholding as well as edge detection are successfully demonstrated by this non-linear imager.Index Terms-CMOS image sensor, image thresholding, non-linear photo-response, pixel circuit.

This design case chronicles a photography assignment starting with its origins in the master’s level lab of a communications design program in Taiwan’s National Yunlin University of Science and Technology, directed by Jalin Huang. We follow this assignment through its adaptation for a basic media development course taught by Professor Elizabeth Boling in the instructional design master’s program at Indiana University, and on to its evolution as a learning exercise and communication device in the instructional design studio sequence of that same program. Along the way, Yichuan Yan, a student from the development course, discusses the experience of receiving and carrying out this assignment in the context of the media development course. Revisions to the assignment for the communications students in Taiwan are also discussed.