Due to consumers' demand for faster picture shot time in the rapidfy expanding digital still camera market, it is of importance to address the real-time implementation issues in the development of passive automatic focusing for digital still cameras. This article discusses such real-time implementation issues that are often overlooked when designing passive contrast sensing automatic focusing on digital still camera processors. Specifically, algorithmic design tradeoffs between automatic focusing speed, accuracy, and power consumption, are addressed. A sample implementation and its performance results on an actual digital still camera hardware platform powered by the Texas Instruments TMS320DM270 processor are presented to further convey these real-time implementation issues.