Complementary colors and demosaicing, How demosaicing works – ALLIED Vision Technologies Guppy F-503 User Manual

Page 108

Description of the data path

GUPPY Technical Manual V7.1.0

108

Complementary colors and demosaicing

The interlaced SONY CCDs use the four complementary colors Ye (=yellow), Cy
(=cyan), Mg (=magenta) and G (=green) instead of R, G, B (red, green, blue).

Advantage of using complementary colors:

•

Less energy needs to be filtered out. That means an increase of sensitiv-
ity (compare the spectral sensitivity diagrams in Chapter

Spectral sensi-

tivity

on page 53)

Disadvantage of complementary colors:

•

Fully saturated primary colors (e.g. red or blue) cannot be displayed as
well as with primary (RGB) color filters

How demosaicing works

The generation of the output signal luma (Y) and the two chrominance (C)
signals (R-Y) and (B-Y) can be done relatively easy by vertically averaging
the charges of two adjacent lines either in the analog domain (by field read-
out of the CCD in Format_7 Mode_0) or by a digital representation of this
calculation process in Format_7 Mode_1 because of frame integration.

It is now important that due to the changed ordering of Mg and G in every
second line, the vertical averaging of the first two adjacent lines, starting
from the bottom gives:

(Cy + G) and (Ye + Mg),

and the second two lines from the bottom give:

(Cy + Mg) and (Ye + G).

As an approximation by SONY, the Y signal is created by adding horizontally
adjacent pixels, and the chroma signal is generated by subtracting these
adjacent pixel signals.

Note



Color correction: see Chapter

Color correction (only inter-

laced GUPPYs)

on page 113.

BAYER pattern: see

Figure 96: BAYER pattern of SONY comple-

mentary sensors: 1st line: G - Mg, 2nd line: Cy - Ye

on page

161

Debayering: see Chapter