With Global/Synchronous Shutter, all rows in the ROI are reset first and then exposed simultaneously for a specified time. At the end of the exposure/integration time, each pixel value is transferred immediately to an adjacent storage area to await read-out. The pixel values are then read out row-by-row from storage, building the frame. This use of intermediate storage reduces the gradual overexposure that can occur down the image when the rows are read out directly from the active area.
Because all rows are exposed simultaneously, Global Shutter avoids jagged or blurred affect produced by Rolling Shutter for fast action images. However, because it stops exposure to perform read-out, it does not provide the fastest possible sequence of frames.
When to Use
Global Shutter mode is preferred use for fast-motion shots, to avoid blurring. Global Shutter mode should also be used in-conjunction with strobe illumination. Additionally, Global Shutter allows dark and light areas within the ROI to be exposed for different fractions of the exposure time. This can be accomplished with the Extended Shutter feature.
When Not to Use
Since the pixels are read out line by line after integration, no integration is possible during read out. Hence if speed (a high frame rate) is the main consideration, use Rolling Shutter if the circumstances allow it.
How to Use
Global Shutter requires a trigger event to reset the pixel data and start exposure for the entire ROI (as opposed to Rolling Shutter, in which exposure is an on-going process).
When a trigger is used, the camera exposes the region of interest (ROI) in “Global Shutter” mode. That is, all pixels are exposed simultaneously during a set exposure time, then exposure is stopped for the entire image. The trigger event can be generated internally in the camera hardware, externally via the trigger input on the machine vision connector, or by software. See section on Trigger and GPOs for more information.