Instruction manual

Guppy Technical ManualV7.4.0
85
Description of the data path
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 sensitivity
(compare the spectral sensitivity diagrams in Chapter Spectral sensitivity
on page 39)
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) sig-
nals (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 readout of the
CCD in Format_7 Mode_0) or by a digital representation of this calculation pro-
cess 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 bot-
tom 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 adja-
cent pixels, and the chroma signal is generated by subtracting these adjacent
pixel signals.
Note

Color correction: see Chapter Color correction (only interlaced
Guppys) on page 89.
BAYER pattern: see Figure 88: BAYER pattern of SONY comple-
mentary sensors: 1st line: G - Mg, 2nd line: Cy - Ye on page 136
Debayering: see Chapter Format_7 Mode_0: sensor readout
and color on page 87 and Chapter Format_7 Mode_1: sensor
readout and color on page 88
Using Red, Green, Blue Using Yellow, Cyan, Magenta, Green
+ increases color resolution - decreases color resolution
- decreases sensitivity + increases sensitivity
Table 33: Comparison RGB and CMYG