Considerations When Using Binning - Basler acA2040-55 User Manual

AW00123409000 Features
7.8.4

Considerations When Using Binning

Increased Response to Light
Using binning can greatly increase the camera's response to light (sensitivity). When binning is
enabled, acquired images may look overexposed. If this is the case, you can reduce the lens
aperture, the intensity of your illumination, the camera's exposure time setting, or the camera's gain
setting.
When using vertical binning on monochrome cameras, the limits for the minimum gain settings are
automatically lowered. This allows you to use lower gain settings than would otherwise be available.
For the lowered limits for the minimum gain settings, see Section 7.2.2 on page 195.
Decreased Resolution
Using binning effectively decreases the resolution of the camera's imaging sensor. For example,
the sensor in the acA640-90um camera normally has a resolution of 659 (H) x 494 (V). If you set
this camera to use horizontal binning by 3 and vertical binning by 3, the effective resolution of the
sensor is decreased to 219 (H) by 164 (V).
Binning's Effect on ROI Settings
When you have the camera set to use binning, keep in mind that the settings for your image region
of interest (ROI) will refer to the binned rows and columns in the sensor and not to the physical rows
and columns in the sensor as they normally would. Another way to think of this is by using the
concept of a "virtual sensor".
For example, assume that you are using an acA640-90um camera set for 3 by 3 binning as
described above. In this case, you would act as if you were actually working with a 219 column by
164 row sensor when setting your ROI parameters. The maximum ROI width would be 219 and the
maximum ROI height would be 164. When you set the Offset X and the Width for the ROI, you will
be setting these values in terms of virtual sensor columns. And when you set the Offset Y and the
Height for the ROI, you will be setting these values in terms of virtual sensor rows and columns.
For more information about the image region of interest (ROI) feature, see Section 7.6 on page 208.
Effective Image ROI and Effective Offset X and Offset Y
Note that neither width nor height of the (physical) sensor used in the above example were evenly
divisible by 3. Each division left a remainder of two. Therefore, the sensor resolution actually used
for binning was 657 (H) x 492 (V), and the remaining two columns (numbers 658 and 659) and rows
(numbers 493 and 494) were excluded from binning and image transmission.
In other words, and expressed in therms of the physical sensor: An effective image ROI was formed
whose resolution of 657 (H) x 492 (V) was smaller than the resolution of the originally set image
ROI. Only the pixels within the effective image ROI were used for binning. And only these pixels
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