Pulsed Illumination Synchronization for Global Reset Rolling Shutter Imagers
Global Reset rolling shutter imagers eliminate motion blur when pulsed light fires strictly within the dark global integration window under controlled ambient light.
Exposure Gradient
Spatial Variation
An unwanted variation in accumulated optical energy across a photosensitive surface occurs when a rolling shutter is paired with continuous motion or dynamic lighting. In high-precision imaging, this exposure gradient creates a non-uniform signal response that distorts the radiometric accuracy of the measurements across the pixel columns. Calibration procedures must account for this spatial disparity to ensure that measurement data remain uniform regardless of the sensor layout.
Metrological Bias
A systematic distortion arises when the exposure time of individual pixel rows begins and ends at different instances. This bias produces a brightness slope across the captured image when the scene illumination fluctuates during the readout sequence. The resulting exposure gradient invalidates traditional flat-field corrections because the non-uniformity is time-dependent rather than static.
High-frequency lighting ripples exacerbate this effect, which shifts the measured intensity values of identical features depending on their vertical coordinates in the image.
Sensor Drift
Thermal fluctuations in the sensor package alter the row-to-row reset and readout delays over extended operating periods. This drift changes the slope of the exposure gradient. Standard laboratory protocols require periodic verification using a stabilized uniform light source.
Correction Protocol
Real-time compensation employs a row-by-row gain adjustment based on the known readout speed of the sensor. Correcting the exposure gradient requires applying a scaling factor that is proportional to the elapsed time between the start of the frame reset and the readout of the final row. This process restores the spatial uniformity of the measurement, though it cannot recover the signal-to-noise ratio lost in the under-exposed regions of the frame.