AVIIVA® EM1
53
1043D - AVIIVA EM1 –04/11
e2v semiconductors SAS 2011
How is performed the Flat Field Correction ?
What is the Flat Field correction (FFC) ?
The Flat Field Correction is a digital correction on each pixel which allows :
¾
To correct the Pixel PRNU (Pixel Response Non Uniformity) and DSNU (Dark Signal Non Uniformity)
¾
To Correct the shading due to the lens
¾
To correct the Light source non uniformity
Before
After
How is calculated / Applied the FFC ?
The FFC is a digital correction on the pixel level for both Gain and Offset.
¾
Each Pixel is corrected with :
o
An Offset on 8 bits (Signed Int 5.3). They cover a dynamic of
±
16LSB in 12bits with a resolution of
1/8 LSB 12bits.
o
A Gain on 14 bits (Unsigned Int 14) with a max gain value of x3
o
The calculation of the new pixel value is :
P’ = ( P + Off).(1 + Gain/8192)
The FFC processing can be completed with an automatic adjustment to a global target. This function is
designed as “
FFC Adjust
”. This adjustment to a User target is done by an internal hidden gain which is re-
calculated each time the FFC is processed while the FFC adjust function is enabled.
The FFC is always processed with the max pixel value of the line as reference. If enabled, the FFC adjust
module (located at the output of the FFC module) calculates the adjustment gain to reach the target
defined by the User.
When the FFC result is saved in memory, the adjust gain and target are saved in the same time in order to
associate this gain value with the FFC result.
