Color correction, Why color correction, Color correction in avt cameras – ALLIED Vision Technologies Guppy PRO F-503 User Manual
Page 138: Color correction: formula, Gretagmacbeth colorchecker
Description of the data path
Guppy PRO Technical Manual V4.0.0
136
Color correction
Why color correction?
The spectral response of a CCD is different of those of an output device or
the human eye. This is the reason for the fact that perfect color reproduction
is not possible. In each Guppy PRO camera there is a factory setting for the
color correction coefficients, see Chapter
Color correction is needed to eliminate the overlap in the color channels. This
overlap is caused by the fact that:
•
Blue light:
is seen by the red and green pixels on the CCD
•
Red light:
is seen by the blue and green pixels on the CCD
•
Green light:
is seen by the red and blue pixels on the CCD
The color correction matrix subtracts out this overlap.
Color correction in AVT cameras
In AVT cameras the color correction is realized as an additional step in the
process from the sensor data to color output.
Color correction is used to harmonize colors for the human eye.
Guppy PRO cameras have the so-called color correction matrix. This means:
you are able to manipulate the color-correction coefficients yourself.
Color correction: formula
Before converting to the YUV format, color correction on all color models is
carried out after BAYER demosaicing via a matrix as follows:
GretagMacbeth ColorChecker
Sensor-specific coefficients C
xy
are scientifically generated to ensure that
GretagMacbeth™ ColorChecker® colors are displayed with highest color fidel-
ity and color balance.
Note
Configuration
Hue and saturation do not show any effect on Guppy PRO
color models in the Raw8 and Raw16 format, because color
processing is switched off in all Raw formats.
Formula 5: Color correction
red*
Crr
red
Cgr
green
Cbr
blue
+
+
=
green*
Crg
red
Cgg
green
Cbg
blue
+
+
=
blue*
Crb
red
Cgb
green
Cbb
blue
+
+
=