Digital Signal Processing Reference
In-Depth Information
Figure 2.3.
one of the more interesting
ones is the YCrCb color space. This is a color space representation
in which you code the pixel value in terms of its brightness
(luminance), and Cr, Cb which is a combination of RGB. This
method of representing color is very useful since the human eye is
very sensitive to brightness or luminance, and much less sensitive
to color. When the pixel value is broken down into luminance and
color, we can get away with using fewer bits (lower resolution) to
encode the color information as the human eye cannot detect the
difference.
YCrCb is another way of encoding the RGB colors
There are many color spaces
e
and using
e
fewer bits in the process
but before the video is displayed we
must reconvert everything to RGB.
The way you convert a pixel value from one color space (RGB)
to another (YCrCb) is to multiply each color component in the
RGB space with a fixed constant
e
see
Figure 2.3
.
In terms of hardware all you need is multipliers and adders to
implement the operation. Any decent processor can do this
FPGAs (field-programmable gate arrays) of course can do this
elegantly and very fast given their inherent DSP (digital signal
processing) capabilities.
When you start converting a pixel value from one color space
to another there are multiple conversions in each stage.
For example:
Convert RGB to YCrCb
e
TRANSMIT
/
Convert back to RGB
PROCESS THE VIDEO
/
/
Convert back to YCrCb
TRANSMIT
/
/
Convert back to RGB
/
DISPLAY
/
2.4 Video Processing Performance
Any video processing signal chain is bound to have many color
space conversions along the way. These conversions have to be
done at the pixel rate, which for HD video is very high.
Consider 1920
60 pixels are
coming in each second. Which means 124.4 million pixels in each
1080 with 60 fps. 1920
1080
