User`s manual

50 Spyder3 GigE Vision SG-14 Monochrome Cameras User’s Manual
03-032-20123-01 Teledyne DALSA
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 ) - digital 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
The algorithm is performed in two steps. The fixed offset (FPN) is determined first by performing a
calibration without any light. This calibration determines exactly how much offset to subtract per pixel in
order to obtain flat output when the CCD is not exposed.
The white light calibration is performed next to determine the multiplication factors required to bring
each pixel to the required value (target) for flat, white output. Video output is set slightly above the
brightest pixel (depending on offset subtracted).
Flat Field Correction Restrictions
It is important to do the FPN correction first. Results of the FPN correction are used in the PRNU
procedure. We recommend that you repeat the correction when a temperature change greater than 10°C
occurs or if you change the analog gain, integration time, or line rate.
PRNU correction requires a clean, white reference. The quality of this reference is important for proper
calibration. White paper is often not sufficient because the grain in the white paper will distort the
correction. White plastic or white ceramic will lead to better balancing.
Note: If your illumination or white reference does not extend the full field of view of the camera, the
camera will send a warning.
For best results, ensure that:
 50 or 60 Hz ambient light flicker is sufficiently low not to affect camera performance and calibration
results.
 For best results, the analog gain should be adjusted for the expected operating conditions and the
ratio of the brightest to darkest pixel in a tap should be less than 3 to 1 where:
 The camera is capable of operating under a range of 8 to 1, but will clip values larger than this ratio.
3>
Darkest Pixel (per tap)
Brightest Pixel (per tap)