Ruben M. Velarde

Real-time scene change detection assisted with camera 3A: auto exposure, auto white balance, and auto focus

Many scene change detection techniques have been developed for scene cuts, fade in and fade out by analyzing video encoder input signals. For real time scene change detection, sensor input signals provide first-hand information which can be used for scene change detection. In this paper, by analyzing camcorder front end sensor input signals with our proposed algorithms based on camera 3A (auto exposure, auto white balance and auto focus), a novel scene change detection technique is described. Camera 3A based scene change detection algorithm can detect scene changes in a timely manner and therefore fits well for real time scene change detection applications. Experimental results show that this algorithm can detect scene changes with good accuracy. The proposed algorithm is computationally efficient and easy to implement.

Exposure preferences for digital still imaging: a psychophysical study

The automatic exposure control (AEC) for a camera phone is typically a simple function of the brightness of the image. This brightness, or intensity, value generated from a frame is compared to a predefined target. If the intensity value is less than a specified target, the exposure is increased. If the value is greater, exposure will be decreased. Is using an intensity target statistic a good model for AEC? In order to answer this question, we conducted psychophysical experiments to understand subjective preferences. We used a high-end DSLR to take 64 different outdoor and indoor scenes. Each scene was captured using five different exposure values (EV), from EV-1 to EV+1 with half EV increments. Subjects were shown the five exposures for each scene and asked to rank them based on their preferences. The collected data were analyzed along different dimensions: preferences as a function of the subjects, EV levels, image quality scores, and the images themselves. Our data analysis concludes that a dynamic intensity target is needed to match the exposure preferences collected from our subjects.