© 2016 Thorlabs Scientific Imaging
2 Camera Basics
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2.3.3 Color Filter (Bayer filter)
For technical reasons, digital image sensors can only detect brightness information, but no color
information. To produce color sensors, a color filter is applied to each photocell (pixel). The
arrangement of the color filters is illustrated in the following figure. Two out of every four pixels have
a green filter, one pixel has a red filter and one has a blue filter. This color distribution corresponds
to the color sensitivity of the human eye, and is called the Bayer filter pattern. With the help of the
Bayer pattern the correct brightness and color information can be calculated for each pixel. Full
sensor resolution is retained.
Bayer conversion
A Bayer conversion, also referred to as de-Bayering, is carried out to determine the color
information from the raw sensor data (raw Bayer). By default all DCx Cameras transmit the image
data to the PC in raw Bayer format. The PC then uses the functions of the uc480 API to convert the
image data to the color format you need for displaying or further processing the data.
To convert the colors, a filter mask moves over the image and calculates a color value for each
pixel from the surrounding pixels. The uc480 API provides two filter masks that differ in image
quality and CPU load.
Normal Quality (Mode IS_CONV_MODE_SOFTWARE_3x3/IS_CONV_MODE_HARDWARE_3x3)
A smaller filter mask is used for conversion. This algorithm has a low load on the CPU. The filter's
averaging function may cause a slight blur. Noise is reduced. This filter is recommended for
image processing tasks.
High Quality (Mode IS_CONV_MODE_SOFTWARE_5x5)
A large filter mask is used for conversion. This algorithm offers very accurate color positioning
and an increased level of detail. The CPU load is higher than with the normal filter. This filter is
recommended for visualization applications.
Note
Software conversion with high quality should only be used for sensors whose green pixels have the
same sensitivity. This applies to the following sensors:
DCU223C / DCU224C
DCC1240C, DCC3240C
For all other sensors, we recommend using the standard filter mask.
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