Dalsa Spyder3 SC-30-02K80-00-R, User Manual

Page: 44 / 111

44 Spyder3 Color Manual
03-032-20059-01 DALSA
Digital Processing
To optimize camera performance, digital signal processing should be completed after any
analog adjustments.
1. Fixed pattern noise (FPN) calibration (calculated using the
ccf
command) is used to
subtract away individual pixel dark current.
2. Photo-Response Non-Uniformity (PRNU) coefficients (calculated using the
cpa
command) are used to correct the difference in responsivity of individual pixels (i.e.
given the same amount of light different pixels will charge up at different rates) and
the change in light intensity across the image either because of the light source or due
to optical aberrations (e.g. there may be more light in the center of the image). PRNU
coefficients are multipliers and are defined to be of a value greater than or equal to 1.
This ensures that all pixels will saturate together.
3. Background subtract (
ssb
command) and system (digital) gain (
ssg
command) are
used to increase image contrast after FPN and PRNU calibration. It is useful for
systems that process 8-bit data but want to take advantage of the camera‘s 12 bit
digital processing chain. For example, if you find that your image is consistently
between 128 and 255 DN (8 bit), you can subtract off 128 (
ssb 2048
) and then
multiply by 2 (
ssg 0 8192
) to get an output range from 0 to 255 DN.
Calibrating the Camera to Remove Non-Uniformity
(Flat Field Correction)
Please note: description is preliminary and subject to change.
Flat Field Correction Overview
This camera has the ability to calculate correction coefficients in order to remove non-
uniformity in the image. This video correction operates on a pixel-by-pixel basis and
implements a two-point correction for each pixel. This correction can reduce or eliminate
image distortion caused by the following factors:

Fixed Pattern Noise (FPN)

Photo Response Non Uniformity (PRNU)

Lens and light source non-uniformity
Correction is implemented such that for each pixel:
V
output
=[(V
input
- FPN( pixel ) - black level offset) * PRNU(pixel) – Background Subtract] x System Gain
where V
output
= digital output pixel value
V
input
= digital input pixel value from the CCD
PRNU( pixel) = PRNU correction coefficient for this pixel
FPN( pixel ) = FPN correction coefficient for this pixel
Background Subtract = background subtract value
System Gain = digital gain value