Prnu (Pixel Response Non-Uniformity ) Correction - JAI LT-200CL User Manual

The following drawing shows the characteristics of Knee Point 890LSB and Knee Slope
1000h.
1279
1023
968
890
[100%]
32
[0%]
0
0 102
Fig.19
6.3.10

PRNU (Pixel Response Non-Uniformity ) correction

PRNU (Pixel Response Non-Uniformity) is, as the name implies, a non-uniformity of the
response of each individual pixel. This means that for a fixed light level each pixel will
have a slightly different output level (response).
Before correction: Non-uniform response from pixel to pixel
Multiply
by
Factor < 1
Multiply
by
Factor > 1
Fig.20 Conceptual drawing for PRNU correction (1)
To correct for PRNU, the camera‟s internal correction circuit captures one or several
lines of data under non-saturated illuminated conditions which are not more than 80% of
maximum (recommend level is half of maximum), and the average across the line is
calculated. Based on this average, coefficients are then generated for each individual
pixel. The coefficient has the function of multiplying the pixel output with a factor
greater or less than 1. These coefficients are stored in a non-volatile memory, and are
therefore maintained after power down.
Fig.21 Conceptual drawing for PRNU correction (2)
LT-200CL
Knee Point = 37Ah (890)
Knee Slope = 1000h (1/16)
In this case : Maximum Value is 968 LSB.
2848
Input Data Level
Knee and knee slope characteristics
After correction: flat response from pixel to pixel
1/16
Knee Point
4095
19
Max
Average
Min
Average