8.Features
© 2023 China Daheng Group, Inc. Beijing Image Vision Technology Branch 115
8.4.10.
Lookup Table
When the analog signal that is read out by the sensor has been converted via ADC, generally, the raw
data bit depth is larger than 8 bits, it is 12 bits. The feature of lookup table is to replace some pixel values
in the 8 bits and 12 bits images by values defined by the user.
The lookup table can be a linear lookup table or a non-linear lookup table, created entirely by the user.
You can also use the LUTValueAll function to create an entire lookup table.
1)
How it works
a)
LUT is short for “lookup table”, which is basically an indexed list of numbers.
b)
In the lookup table you can define replacement values for individual pixel values. For example, you
can replace a gray value of 0 (= minimum gray value) by a gray value of 4095 (= maximum gray value
for 12-bit pixel formats). This changes all completely black pixels in your images to completely white
pixels.
c)
Setting a user-defined LUT can optimize the luminance of images. By defining the replacement values
in advance and storing them in the camera to avoid time-consuming calculations. The camera itself
has a factory default lookup table, and the default lookup tables do not affect image luminance.
2)
Creating the user-defined LUT
To create a lookup table, you need to determine the range of LUTIndex and LUTValue parameters by the
maximum pixel format supported by the currently used camera.
On cameras with a maximum pixel bit depth of 12 bits
The LUTIndex selectable item is 0-4095, each LUTIndex corresponds to a LUTValue, and the LUTValue
range is [0,4095].
Create a user-defined lookup table with the following steps:
1)
Select the lookup table to use. Since there is only one user-defined lookup table in the camera, there
is no need to select it by default.
2)
Set the LUTIndex parameter to the pixel value that you want to replace with a new value.
3)
Set the LUTValue parameter to the new pixel value.
4)
Repeat steps 1 and 2 for all pixel values that need to be changed to set the parameters to the target
pixel values in turn.
5)
Set the LUTEnable parameter to true means that the lookup table feature is enabled. The default is
disabled.
If you want to replace all pixel values, it is recommended to use the LUTValueAll function. See the
LUTValueAll sample code in the Development User Manual for details.
