Pyramid Imaging EXO Series, Manual

Page: 54 / 135

SVS-VISTEK
Feature-Set 54
7.1.9 Color
Color cameras are identical to the monochrome versions. The color pixels
are transferred in sequence from the camera, in the same manner as the
monochrome, but considered as “raw”-format.
The camera sensor has a color mosaic filter called “Bayer” filter pattern
named after the person who invented it. The pattern alternates as follows:
E.g.: First line: GRGRGR... and so on. (R=red, B=blue, G=green)
Second line: BGBGBG... and so on. Please note that about half of the
pixels are green, a quarter red and a quarter blue. This is due to the
maximum sensitivity of the human eye at about 550 nm (green).
Using color information from the neighboring pixels the RG and B values
of each pixel is interpolated by software. E.g. the red pixel does not have
information of green and blue components. The performance of the
image depends on the software used.
NOTICE
It is recommended to use a IR cut filter for color
applications!
White Balance
The human eye adapts to the definition of white depending on the lighting
conditions. The human brain will define a surface as white, e.g. a sheet of
paper, even when it is illuminated with a bluish light.
White balance of a camera does the same. It defines white or removes
influences of a color tint in the image.
Influences normally depend on the light source used. These tints are
measured in Kelvin (K) to indicate the color temperature of the
illumination.
Light sources and their typical temperatures:
Temperature Common Light Source
10.000 – 15.000 K Clear Blue Sky
6.500 – 8.000 K Cloudy Sky / Shade
5.500 – 6500 K Noon Sunlight
5.000 – 5.500 K Average Daylight
4.000 – 5.000 K Electronic Flash
4.000 – 5.000 K Fluorescent Light
3.000 – 4.000 K Early AM / Late PM
2.500 – 3.000 K Domestic Lightning
1.000 – 2.000 K Candle Flame
Figure 24: Table of color temperatures
Figure 23: CCD with Bayer Pattern