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Sensor Shutter Modes (global, rolling)

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[카메라·영상]

2019. 10. 24.

Sensor Shutter Modes

Global Shutter Mode

Basic specs

  • Global reset of all photo diodes
  • Integration simultaneously in all photo diodes
  • Global transfer of all photo diode signals in sensing nodes
  • Readout line by line

Artifacts caused by subject movement

Exposure time is too long - during exposure the subject is displaced because of the blurring of captured image.

Left: Original without movement
Right: Image blurred due to movement

To prevent this artifact a shorter exposure needs to be used.
The exposure time must be short enough so the object projection will not move more than one pixel distance on the sensor to get the blur of the image under one pixel.

Other solution is to use dark environment and use flash with short light pulse which will freeze the motion.

Rolling Shutter Mode

Basic specs

  • Line by line integration state
  • Line by line transfer and readout
    Integration of next line is delayed by readout time of one line

Artifacts caused by subject movement

Because of the sequential start of exposure lines the moved object will be deformed.
It depends on direction of movement:
When moving in direction of lines (horizontal) the image will be skewed.
When moving in vertical direction the object may become longer or shorter.

When the exposure is longer, motion blur may also occur.



To prevent these artifacts exposure with flash has to be used.
The flash strobe may occur only when all lines are exposing simultaneously.
The delay from exposure start depends on sensor type and readout.

The delay between exposure start and light strobe has to be longer than frame time at shortest exposure (1/fps).
This is also limiting the exposure time which must be also longer than frame time to get short time slot when all lines will be exposing.

Global Reset Release Mode

Basic specs

  • Global reset of all photo diodes
  • Integration stage
  • Transfer, conversion and readout line by line starts at the end of the integration of the first line. Lines that do not transfer stay in the integration stage.

Artifacts caused by subject movement

Because of longer exposure of lower lines they may be blurred more than the top ones.

To freeze the motion the flash has to be used in dark environment.
However, compared to rolling shutter the flash strobe does not need to be delayed.