The MMS Continuous Auto Focus keeps the scene in focus during the preview and movie encoder operation by using advanced algorithms for scene change detection and object tracking, as wel as advanced driving methods to minimize the scene blurring during the focus search operation.
The MMS single and continuous focus were developed and working in practically all industry wide lens actuator technologies – VCM, HVCM, piezo, piezo + position sensor, stepper motors, variable focal length lenses.
- VCM ringing compensation
- part of MMS SAF/CAF is lens driving method using SW VCM ringing compensation, which guarantees best focusing in very bright conditions (exposure time less then lens ringing period)
- AF can utilize the CAF result to skip or speed-up scanning
- Uses gyroscope sensor and frame analysis data to detect handshake or moving scene during scanning
- Support for stereo capturing
- Support face and touch focus modes
- No scanning before capture if CAF has focused during preview
- Optimized for TI OMAP
Many CAF algorithms (including IPhone) use normal SAF scanning for CAF – they detect scene change during preview and run normal SAF scan. This creates significant zoom-like effect during scanning, which is not pleasing to the user. MMS CAF is a different algorithm which targets:
- Minimum best-focus overshoot (minimum zoom-effect)
- Multi-scan if needed in very low light conditions, enabling CAF to focus reasonably down to ~1 Lux
- Smooth (tunable) lens moving
- Sophisticated scene change and scene stability detection, based on both scene analysis and gyroscope data
- Intelligent scanning failure handling – where the lens should go if scanning fails
- Detection of instable scene appeared during scanning, based on both scene analysis and gyroscope data
- Detection of single hand-shake affected frames
- “Sky detection” and “Flat scene detection” to avoid scanning the whole range to check whether the sky is a “very-macro object” (when the user points the camera to sky or flat area)
- Flexible tuning, including separate tuning for still preview and video, precise control of scanning speed
The trade-off “overshoot versus accuracy” can be tuned such that to achieve best accuracy for still capture or minimum overshoot for video.