The camera industry is pursuing advanced — beyond HD — camera technology. These advances include both higher temporal resolution and higher spatial resolution. The latter, in turn, forces changes in the choice of a lens for use with an advanced camera.
Sensors and processing
The earliest of the recent advances in camera technology is the switch from CCD to CMOS sensors. One problem, banished by CMOS, is vertical smear. Unfortunately, this step forward has been achieved with a step backward. Rolling shutter artifacts are present when there is motion by the camera and/or objects moving within the frame. Slight random movements by a handheld camera can create a wobbly gelatin look that is particularly disturbing.
Because a CMOS sensor’s rows are processed — reset, integrated and output — in a sequence that occurs over time, a CMOS sensor exposes each frame in a top-to-bottom pattern. The row-exposure offset creates a rolling-shutter skew. (See Figure 1.) To date, the most common solution has been to read out multiple vertical slices of the image simultaneously. The more slices a chip can output, the faster a whole image is captured — and the less rolling shutter artifacts.
Most CMOS imagers today use active-pixel sensor (APS) technology that is implemented by three transistors. Each pixel has a reset transistor, an amplifier transistor and a row select transistor.
By adding a fourth transistor to each pixel’s circuitry, it is possible to capture an image with all sensor pixels simultaneously. All sensor photodiodes are reset at the same instant. By beginning image capture at the same moment in time, there is no row-exposure offset to cause rolling shutter. The fourth transistor holds a photodiode’s integration value until it can be read out. This global shutter design eliminates rolling shutter.