Digital Image Formats - A Practical Guide to Video and Audio Compression - page 137

Red

Green

Blue

Figure 6-15 Bayer color-filter array.

6.12.2 Color-Filter Array

Figure 6-15 shows a typical color-filter array with the green channel arranged in what is
called a Bayer dithering pattern. This has two green quadrants for every cell and one each
of red and blue. Because the eye is most sensitive to green and the dominant component
of a luma signal is green, this enhances the perceived resolution.
This is fine for still cameras and for low-cost video cameras but it doesn't provide the
desired quality for professional users. The main disadvantage is that the spatial resolution
is traded off and the red and blue are recorded at half the resolution of the green, and that
is only half the spatial resolution available on the sensor. The colored pixels are also offset
spatially and fine detail may only be recorded in one channel or the other. The effective
resolution is about a quarter that of the CCD array.

6.12.3 Prisms and Multiple CCD Sensors

The beam-splitting prism and 3 CCD chip arrangements are a much better solution. The
4-chip cameras are essentially similar but have a slightly more complex prism arrange-
ment inside.
The main advantage here is that the three CCD sensors can operate at full resolu-
tion—there is no loss of detail and all the colors are spatially aligned. These cameras are
more difficult to manufacture and the optical effects of the prisms compromise some of the
lens choices that are available, but the qualitative gains are worth it.
You can find more information about how these color cameras and sensors work at
the Dalsa Digital Cinema Web site.

6.13 Color Spaces

There are many other ways that color images are represented, some of which come from
the still-image formats. There are implications for this when compressing video because

Dalsa Digital Cinema: http://www.dalsa.com/dc