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between larger signals. For most applications, the ISC-178x default gain setting optimizes the
balance between small signals and large signals.
Figure 17.
Effect of Gain on the Video Signal
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A.
B.
C.
1. Low Gain
2. Medium Gain
3. High Gain
In figure A, low gain has been applied to the signal. The pixel values in the image are grouped
close together. In figure B, medium gain has been applied to the signal. There are now more
notable differences in pixel value within the image. In figure C, high gain has been applied to
the signal. At high gain, mid-range and bright portions of the image are now both represented
as white, the highest pixel value. In figure C, several bright areas of the image have been
clipped to the maximum pixel value, and you can no longer distinguish subtle shading in the
brightest areas of the image.
Gain can be useful when there is not enough available light and you need to increase the
brightness of images. However, increasing gain multiplies both the signal and noise. When
possible, it is preferable to add additional lighting.
Auto White Level (Color Models Only)
Color models of the ISC-178x allow you to adjust the gain for each color plane in the RGB
color space. The white level specifies the point at which values in the red, green, and blue
color planes converge to produce white. To obtain an accurate white level, either adjust each
gain value manually or use automatic white level adjustment with a test image. For best results
the image should contain a neutral reference, such as a gray piece of paper or a reference card.
There are multiple ways to adjust gain values or enable automatic white balance adjustment:
•
MAX—Use the settings on the Color tab of the device configuration page to adjust gain
levels or enable automatic white level adjustment.
•
Vision Builder AI—Use the settings on the Color tab of the Acquire Image (Smart
Camera) step to adjust gain levels or enable automatic white level adjustment.
Black Level
The black level specifies the image brightness. Set the black level to the pixel value which
corresponds to true black. If the black level is inaccurate, near-black pixels may be displayed
as black or black objects may appear gray in the output image.
ISC-178x User Manual
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© National Instruments
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