Luminance Lookup Table; Lookup Table - Basler GIGE VISION ace acA640-100gm/gc Manual

Area scan cameras

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10.8 Luminance Lookup Table

10.8.1

Pixel data from the imaging sensor is digitized by the ADC at 12 bit depth. Whenever the camera

is set for a 12 bit pixel format (e.g., Mono 12), the 12 bits transmitted out of the camera for each

pixel normally represent the 12 bits reported by the camera's ADC. The luminance lookup table

feature lets you use a custom 12 bit to12 bit lookup table to map the 12 bits reported out of the ADC

to 12 bits that will be transmitted by the camera.

The lookup table is essentially just a list of 4096 values, however, not every value in the table is

actually used. If we number the values in the table from 0 through 4095, the table works like this:

The number at location 0 in the table represents the 12 bits that will be transmitted out of the

camera when the ADC reports that a pixel has a value of 0.

The numbers at locations 1 through 7 are not used.

The number at location 8 in the table represents the 12 bits that will be transmitted out of the

camera when the ADC reports that a pixel has a value of 8.

The numbers at locations 9 through 15 are not used.

The number at location 16 in the table represents the 12 bits that will be transmitted out of the

camera when the ADC reports that a pixel has a value of 16.

The numbers at locations 17 through 23 are not used.

The number at location 24 in the table represents the 12 bits that will be transmitted out of the

camera when the ADC reports that a pixel has a value of 24.

And so on.

As you can see, the table does not include a user defined 12 bit value for every pixel value that the

sensor can report. So what does the camera do when the ADC reports a pixel value that is between

two values that have a defined 12 bit output? In this case, the camera performs a straight line

interpolation to determine the value that it should transmit. For example, assume that the ADC

reports a pixel value of 12. In this case, the camera would perform a straight line interpolation

between the values at location 8 and location 16 in the table. The result of the interpolation would

be reported out of the camera as the 12 bit output.

Another thing to keep in mind about the table is that location 4088 is the last location that will have

a defined 12 bit value associated with it. (Locations 4089 through 4095 are not used.) If the ADC

reports a value above 4088, the camera will not be able to perform an interpolation. In cases where

the ADC reports a value above 4088, the camera simply transmits the 12 bit value from location

4088 in the table.

The advantage of the luminance lookup table feature is that it allows a user to customize the

response curve of the camera. The graphs below show the effect of two typical lookup tables. The

first graph is for a lookup table where the values are arranged so that the output of the camera

increases linearly as the digitized sensor output increases. The second graph is for a lookup table

where the values are arranged so that the camera output increases quickly as the digitized sensor

output moves from 0 through 2048 and increases gradually as the digitized sensor output moves

from 2049 through 4096.

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Lookup Table

Standard Features

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Luminance Lookup Table; Lookup Table - Basler GIGE VISION ace acA640-100gm/gc Manual

10.8 Luminance Lookup Table

Lookup Table

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