Calculating Global Overlap Windows in Sequential Row Readout Image Sensors
Calculate global overlap by subtracting array readout time from total exposure; fire external illumination within this window to emulate global shuttering.
Vertical Blanking
Temporal Gap
Time interval between the end of the last active line of one video frame and the start of the first line of the next frame allows for internal processing and synchronization. The vertical blanking provides a window where the sensor can reset its circuitry or transfer data to the output registers. This period was originally designed to allow the electron beam in a cathode ray tube to return to the top of the screen.
Data Carriage
Modern digital systems often use this quiet time to transmit non image information such as metadata, timecodes, system status and error correction codes. Because no image data is being sent, the vertical blanking provides a dedicated channel for communication between the sensor and the host processor. The duration of this gap can be adjusted to change the frame rate.
Power Management
Reducing activity during the idle phase helps to lower the overall heat dissipation of the sensor chip. Some devices enter a low power state during the vertical blanking to extend battery life in portable applications. This duty cycle management is a standard feature in mobile imaging hardware.
Exposure Control
Adjusting the length of the pause allows the system to fine tune the integration time without changing the master clock frequency. The vertical blanking interval must be long enough to accommodate the longest exposure required by the application.