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Sensor Shutter Modes

Sensor shutter modes can be changed with the xiAPI parameter XI_PRM_SHUTTER_TYPE.
The support of shutter modes is dependent on the sensor's capabilities.

Global Shutter Mode

What is Global shutter mode:

Basic specs

  • Global reset of all photodiodes
  • Integration simultaneously in all photodiodes
  • Global transfer of all photodiode 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 the 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.

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

Rolling Shutter Mode

What is Rolling shutter mode:

Basic specs

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

Artifacts caused by subject movement

Because of the sequential start of exposure lines, the moving object will be deformed.
It depends on the direction of movement:
When moving in direction of lines (horizontal) the image will be skewed.
When moving in a 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 exposed 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 a frame time at the shortest exposure (1/fps).
This is also limiting the exposure time which must also be longer than the frame time to get a short time slot when all lines will be exposing.

Global Reset Release Mode

What is the Global reset release (GRR) mode:

Basic specs

  • Global reset of all photodiodes
  • Integration stage
  • Transfer, conversion and readout line by line start 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 a 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 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
xiMU models Rolling shutter Global Reset Release
xiQ models Global shutter Global shutter
xiC models Global shutter Global shutter
xiD models Global shutter Global shutter
xiX models Global shutter Global shutter
xiSpec models Global shutter Global shutter
xiB models Global shutter Global shutter
xiB-64 models Global shutter Global shutter
xiRay models Various Various*
xiJ models Various Various*

*Check per model