XIIMUS R-GB-IR CL User Manual. Version 1.2
3.8.
Programmable digital gains (addresses 205 to 207)
The Digital Gain function can be applied individually to each colour channel. Digital gains are
implemented by shifting the original 12-bit data upwards (left) by 0 to 7 positions –
corresponding to range from 1x to 128x accordingly – and by limiting the overflow of the new,
shifted value. The effect is that the response of the camera will be higher, but the effective
noise levels will increase respectively. Please note that after shifting, the lowest bits will be
replaced by zeroes – for example in 8-bit applications (using to topmost 8 bits) and with 128x
gains, three LSBs will be constantly zero when the correction unit is not enabled.
Address for modifying the Digital Gain function:
Function decimal
hexadecimal
binary
Digital Gain InfraRed
205 CD
1100
1101
Digital Gain Red
206 CE
1100
1110
Digital Gain Bluegreen
207 CF
1100
1111
This function is used like the setting of the gains (see above). The data byte consists of eight
bits, which are labelled as follows (MSB first):
X X X X X D2 D1 D0
The last 3 bits are used for each colour channel (see table below). As default, these are all
zeros, and there is no need to change them due to the sensitivity of the camera. They can,
though, be used in cases where lighting is insufficient or to compensate for reducing working
aperture size to decrease blur in the image.
D2 D1 D0 Function
0
0
0
1x digital gain (initial value)
0
0
1
2x digital gain
0
1
0
4x digital gain
0
1
1
8x digital gain
1
0
0
16x digital gain
1
0
1
32x digital gain
1
1
0
64x digital gain
1
1
1
128x digital gain
The bits marked X can be either '1' or '0'.
Examples:
To remove the digital gains on the infrared channel send a 2-byte set 205 (decimal) and 0.
Set all the channels to 4x digital gain by sending 205 followed by 2, 206 followed by 2 and
207 followed by 2.
The lighting used has a small portion of bluegreen, a little more red and a lot of infrared. The
normal gain setting does not produce enough signal (DU) to balance the camera to a
reasonable signal level. The user sets the bluegreen channel to 8x and red to 4x digital gain
to compensate for poor lighting by sending 207 followed by 3 and 206 followed by 2. The
infrared channel is at the initial default value.
© TVI Vision, 18 October 2006 page 44 ( 57 )
