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.
Shutter Extinction Ratio
Contrast Metric
Ratio between the light transmitted when a shutter is open and the light that leaks through when it is closed defines the ability of a system to block unwanted exposure. The shutter extinction ratio determines the purity of the signal in high contrast scenes or when using pulsed light sources. A low ratio leads to ghost images or elevated background noise.
Global Shutter
Sensors that expose all pixels simultaneously rely on an internal storage area that must be shielded from light during the readout process. The shutter extinction ratio in these devices measures how well the storage gate prevents new photons from contaminating the stored charge. Poor isolation results in a vertical smear as light leaks in while the data moves out.
Mechanical Limitation
Physical blades or rotating disks offer very high blocking power compared to electronic gates. These mechanical systems achieve a superior shutter extinction ratio because the opaque material provides near total attenuation of the incident light. Electronic shutters are limited by the transparency of the semiconductor layers.
Wavelength Dependence
Rejection efficiency often varies across the spectral range of the sensor. A shutter extinction ratio that is high for visible light might drop significantly in the infrared region where silicon becomes more transparent.