Image Processing; Basic Construction; Shading Compensation - IAI AT-200GE User Manual

11. Image processing

11.1. Basic construction

The AT-200GE is a 3CCD camera equipped with F4, 1/1.8 inch prism optics. Red,
green and blue color signals are taken from each 2 mega CCD which are filtered to the
red, green and blue spectral wavelengths. A 32-bit microprocessor controls all
functions in the AT-200GE 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 30- or 24-bit RGB pixel format via GigE Vision interface.
Light

11.2. Shading compensation

The AT-200GE 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-200GE has two shading compensation circuits.
1. Color shading compensation
In this mode, the shading is compensated using the G channel as the reference.
Adjust R and B channels to match the characteristics of the G channel. Use white
balance to match R, G and B levels.
Fig.48 Conceptual drawing for color shading compensation
AT-200GE
CCD
CCD
CCD
Fig.47 Principle diagram for signal processing
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B ch
A/D & process circuit
Blemish compensation
Shading compensation
Color matrix
LUT/Gamma/Knee
G ch
A/D & process circuit
Blemish compensation
Shading compensation
Color matrix
LUT/Gamma/Knee
R ch
A/D & process circuit
Blemish compensation
Shading compensation
Color matrix
LUT/Gamma/Knee