Introduction to SenseCam
SenseCam is a wearable digital camera that is designed to take photographs passively, without user intervention, while it is being worn. Unlike a regular digital camera or a cameraphone, SenseCam does not have a viewfinder or a display that can be used to frame photos. Instead, it is fitted with a wide-angle (fish-eye) lens that maximizes its field-of-view. This ensures that nearly everything in the wearer’s view is captured by the camera, which is important because a regular wearable camera would likely produce many uninteresting images.
SenseCam also contains a number of different electronic sensors. These include light-intensity and light-color sensors, a passive infrared (body heat) detector, a temperature sensor, and a multiple-axis accelerometer. These sensors are monitored by the camera’s microprocessor, and certain changes in sensor readings can be used to automatically trigger a photograph to be taken.
For example, a significant change in light level, or the detection of body heat in front of the camera can cause the camera to take a picture. Alternatively, the user may elect to set SenseCam to operate on a timer, for example taking a picture every 30 seconds. We have also experimented with the incorporation of audio level detection, audio recording and GPS location sensing into SenseCam although these do not feature in the current hardware.
In our current design (v2.3), users typically wear the camera on a cord around their neck, although it would also be possible to clip it to pockets or belts, or to attach it directly to clothing. There are several advantages of using a neck-cord to wear the camera. First, it is reasonably stable when being worn, as it tends not to move around from left-to-right when the wearer is walking or sitting. Second, it is relatively comfortable to wear and easy to put on and take off. Third, when worn around the neck, SenseCam is reasonably close to the wearer’s eyeline and generates images taken from the wearer’s point of view – i.e., they get a ‘first person’ view. Informal observations suggest that this results in images that are more compelling when subsequently replayed.
SenseCam takes pictures at VGA resolution (640x480 pixels) and stores them as compressed .jpg files on internal flash memory. We currently fit 1Gb of flash memory, which can typically store over 30,000 images. Most users seem happy with the relatively low-resolution images, suggesting that the time-lapse, first-person-viewpoint sequences represent a useful media type that exists somewhere between still images and video. It also points to the fact that these are used as memory supports rather than rich media. Along with the images, SenseCam also stores a log file, which records other sensor data along with their timestamps. Additional user data, such as time-stamped GPS traces, may be used in conjunction with the SenseCam data via time-correlation.