Programming Manual
PHYTEC Messtechnik GmbH 2008 L-720e_0
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The pciGrabber-4x4 is able to convert the images into the
RGB-format and stores the RGB- color triplets in the memory. This
format provides a good base for further processing.
Often the YCrCb-format is more suitable for storage or transfer of
image data, since the data volume is less. Instead of three Byte only
two Byte (one word) are required. The lower eight bits contain the
brightness and the eight upper bits specify the color portion (Cr/Cb).
For each Y-value alternatingly only one color portion Cr or Cb is
associated. So each pixel has only one part of color information either
the red or blue portion. The missing information can be obtained from
the neighboring pixel. The color is transferred and stored only at the
half resolution of the brightness. Since the bandwidth of the color
information is already reduced by the TV system, this procedure does
not mean a real restriction. This data format is denoted asYCrCb4:2:2.
The first pixel of each line delivers Y1,Cr1/2, the second
Y2,Cb1/2 etc.
For the correct recognition of the color information of an image, four
subsequent fields are required to be digitized. Therefore it is not
sufficient to connect the video source only for a short period or to
connect the videosource only for the duration of the digitization of one
field.
In addition the recognition of a field might not work correctly at the
beginning, in case another not synchronized signal from a camera is
applied. In case of fast switching between two signal sources the
digitized image might be incorrect and it is recommended to observe
some time delay.
