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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.

How to Freeze the Motion

When moving object (e.g. on conveyor) is exposed with higher exposure time - resulting image will have Motion Blur.
To avoid Motion Blur the short exposure times or flash light should be used.

Example of Setup:

Sensor width (W) 0.0069m
1280 pixel in horizontal (PX)
Field of view (FOV) 0.2m
Conveyor speed (CS) 0.1m/s

To decrease Motion Blur under one image pixel the following calculation for flash light length can be used:

Pixel distance(PD) W/PX -> 0.0069m/1280pixels = 5.4um.
Pixel distance recalculated FOVPD = FOV/PX = 0.2m/1280 = 156um
During exposure the band should not move more than 156um
Flash Time (FT) should be less than FOVPD/CS = 156um/0.1m/s = 1.56ms

This is short exposure which may lead to usage of flash light in dark environment.
There shorter bright pulse can produce sharper and brighter image.

Camera models and their sensor modes

Camera models and their Sensor Shutter Modes:

Camera model Free run (live) Triggered mode
all MU9 models Rolling shutter Global Reset Release
CURRERA-RL03 Global shutter Global shutter
CURRERA-RL13 Global shutter Global shutter
CURRERA-RL50 Rolling shutter Global Reset Release
all xiQ models Global shutter Global shutter