Image Processing; Basic Construction; Shading Compensation - IAI AT-140GE User Manual

11. Image processing

11.1. Basic construction

The AT-140GE is a 3CCD camera equipped with F4, 1/2 inch prism optics. Red, green
and blue color signals are taken from each of the 1.45-megapixel CCDs which have
been filtered to the appropriate spectral wavelengths. A 32-bit microprocessor
controls all functions in the AT-140GE camera. The CCD sensor output is normalized in
CDS and preamplifiers. The signals are then digitized to 16 bits. Digital gain control,
color matrix, look-up tables and setup can do signal processing in 16 bits before the
signal is converted to a 32- or 24-bit RGB pixel format via the GigE Vision interface.
Light

11.2. Shading compensation

The AT-140GE implements a digital shading compensation circuit for the white
shading which could be caused in the prism or optical system. The whole image is
divided horizontally and vertically and uses the center level as the reference. The
circuit will compensate the difference between the center and each divided area. The
range for compensation is a maximum of 25%. In the factory, the shading
compensation is activated and stored in the "Factory" area of the memory. The user
can uses this data if the shading compensation is ON. The factory default is OFF.
The AT-140GE has two shading compensation circuits.
1. Color shading compensation
In this mode, the shading is compensated using the G channel as the reference.
R and B channels are adjusted to match the characteristics of the G channel. White
balancing can then be used to match the R, G and B levels.
Fig.48 Conceptual drawing for color shading compensation
AT-140GE
CCD
CCD
CCD
Fig.47 Principle diagram for signal processing
B ch
A/D & process circuit
Blemish compensation
Shading compensation
Color matrix
LUT/Gamma/Knee
4
0 50
450 550 600 650 700 750 nm
0
0
G ch
A/D & process circuit
Blemish compensation
Shading compensation
Color matrix
LUT/Gamma/Knee
4
0 50
450 550 600 650 700 750 nm
0
0
R ch
A/D & process circuit
Blemish compensation
Shading compensation
Color matrix
LUT/Gamma/Knee
4
0
50
450 550 600 650 700 750 nm
0
0
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