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Spyder3 SG-34 GigE Vision Color Manual
03-032-20124-00
Teledyne DALSA
bit), you can su btract off 128 (
Background Subtract (D N ) 2048
) and then m u ltip ly by 2 (
D igital Gain
(D N ) 8192
) to get an ou tp u t range from 0 to 255.
6.
The
Color Correction Value
(as p art of the
Color Matrix
featu re, see p age 48.) ad d s color sp ace
conversion fu nctionality to the cam era, allow ing you to im p rove the color resp onse.
Calibrating the Camera to Remove Non-
Uniformity (Flat Field Correction)
Calibration Overview
When a cam era im ages a u niform ly lit field , id eally, all of the p ixels w ill have the sam e gray valu e.
H ow ever, in p ractice, this is rarely the case (see exam p le below ) as a nu m ber of factors can contribu te to
gray scale non -u niform ity in an im age: Lighting non -u niform ities and lens d istortion, PRN U (p ixel
resp onse non-u niform ity) in the im ager, FPN (fixed p attern noise) in the im ager, etc.
Figure 24. Image with non-uniformities
By calibrating the cam era you can elim inate the sm all gain d ifference betw een p ixels and com p ensate for
light d istortion. This calibration em p loys a tw o -p oint correction that is ap p lied to the raw valu e of each
p ixel so that non -u niform ities are flattened ou t. The resp onse of each p ixel w ill ap p ear to be virtu ally
id entical to that of all the other p ixels of the sensor for an equ al am ou nt of exp osu re.
Correction Overview
This cam era has the ability to calcu late correction coefficients in ord er to rem ove non -u niform ity in the
im age. This vid eo correction op erates on a p ixel-by-p ixel basis and im p lem ents a tw o p oint correction for
each p ixel. This correction can red u ce or elim inate im age d istortion cau sed by the follow ing factors:
Fixed Pattern N oise (FPN )
Photo Resp on se N on Uniform ity (PRN U)
Lens an d light sou rce non -u niform ity
Correction is im p lem ented su ch that for each p ixel:
V
output
=[(V
input
- FPN( pixel ) - digital offset) * PRNU(pixel) – Background Subtract] x System Gain
w here
V
ou tp u t
=
d igital ou tp u t p ixel valu e
V
inp u t
=
d igital inp u t p ixel valu e from the CCD
PRN U( p ixel)
=
PRN U correction coefficient for this p ixel
FPN ( p ixel )
=
FPN correction coefficient for this p ixel
Backgrou nd Su btract
=
backgrou nd su btract valu e
System Gain
=
d igital gain valu e
