Electronic Shutter Types#

The shutter type determines the way in which image data is captured and processed. Depending on the design of the image sensor, your camera model has more than one shutter type.

If your camera model has more than one shutter type, see the Sensor Shutter Mode topic for information about how to change shutter types.

Advantages and Disadvantages#

Available Shutter Types#

Global Shutter#

During image acquisition, all of the sensor's pixels start exposing at the same time and also stop exposing at the same time. Immediately after the end of exposure, pixel data readout begins and proceeds row by row until all pixel data has been read. This is particularly useful if you want to capture fast moving objects or if the camera is moving rapidly while capturing images.

The sensor readout time is the sum of all row readout times. Therefore, the sensor readout time is influenced by the image ROI height. You can determine the readout time by checking the value of the camera's SensorReadoutTime parameter.

On some camera models, the Sensor Readout Mode feature is available. This feature allows you to reduce the sensor readout time.

Rolling Shutter#

During image acquisition, the camera exposes the pixel rows one after the other, with a temporal offset (t_Row) from one row to the next. With this method, the ambient noise is typically significantly lower than with the global shutter method.

When frame start is triggered, the camera resets the first row and begins exposing it. For most cameras, this row is the first row of the image ROI.

A short time later (= 1 x t_Row), the camera resets the second row and begins exposing that row. After another short time (= 1 x t_Row), the camera resets the third row and begins exposing that row.

This continues until a last row of pixels is reached. For most cameras, this row is the last row of the image ROI.

The length of t_Row varies by camera model.

The pixel values for each row are read out at the end of the exposure time of each row. The exposure time is the same for all rows. Because the readout time for each row is also tRow, the temporal shift for the end of readout is identical to the temporal shift for the start of exposure.

The sensor readout time is the sum of all row readout times: t_Row x image ROI height.

Therefore, the sensor readout time also depends on the image ROI height. To determine the readout time, check the value of the camera's SensorReadoutTime parameter.

Possible Image Distortion (Rolling Shutter Effect)#

On rolling shutter cameras, if the object or the camera is moving very fast during image capture, image distortion may occur. This is also known as the rolling shutter effect.

This is due to the temporal shift between the start of exposure of the individual rows.

To prevent the rolling shutter effect, Basler recommends the use of flash lighting. Most cameras can supply a Flash Window output signal to facilitate the use of flash lighting.

Exposure Active Signal#

On rolling shutter cameras, if your camera provides an Exposure Active output signal, the Exposure Active signal goes high when the exposure time for line one begins and goes low when the exposure time for the last line ends. This means that the signal width is greater than the exposure time.

Global Reset Release Shutter#

The Global Reset Release (GRR) shutter is a variant of the rolling shutter. It combines the advantages of the global and rolling shutter.

On GRR shutter cameras, all of the pixels in the sensor start exposing at the same time. However, at the end of exposure, there is a temporal offset (t_Row) from one row to the next.

The t_Row values are the same as on rolling shutter cameras and vary by camera model.

With the GRR shutter type, you must use flash lighting. Otherwise, the brightness in the acquired images will vary significantly from top to bottom due to the differences in the exposure times of the individual rows. Also, when you are capturing images of fast moving objects, images can be distorted due to the temporal shift caused by the different exposure end times of the individual rows.

Most cameras can supply a Flash Window output signal to facilitate the use of flash lighting.

External Links#

• White Paper: Global Shutter, Rolling Shutter - Functionality and Characteristics of Two Exposure Methods (Basler)
• Rolling Shutter (Wikipedia)
• Simulation of the rolling shutter effect on a rotating propeller and a moving car (Wikipedia)

Specifics#

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