User`s manual

Spyder 3 GigE User’s Manual
DALSA 03-032-10158-09
67
A2.2 Analog and Digital Signal Processing Chain
Processing Chain Overview and Description
The following diagram shows a simplified block diagram of the camera’s analog and
digital processing chain. The analog processing chain begins with an analog gain
adjustment, followed by an analog offset adjustment. These adjustments are applied to
the video analog signal prior to its digitization by an A/D converter.
The digital processing chain contains the FPN correction, the PRNU correction, the
background subtract, and the digital gain and offset. All of these elements are user
programmable.
Figure 24: Signal Processing Chain

Analog Processing
Digital Processing
anal ogvideo
anal og
gain
anal og
offset
FPN
coefficients
digital
offset
PRNU
coefficients
background
subtract
digitalsystem
gain
digitalvideo
sag,ccg
sao,cao
ccf
sdo
ccp,cpa ssb
ssg
Analog Processing
Optimizing offset performance and gain in the analog domain allows you to achieve a
better signal-to-noise ratio and dynamic range than you would achieve by trying to
optimize the offset in the digital domain. As a result, perform all analog adjustments
prior to any digital adjustments.
1. Analog gain (
58Hsag or 59Hccg command) is multiplied by the analog signal to increase the
signal strength before the A/D conversion. It is used to take advantage of the full
dynamic range of the A/D converter. For example, in a low light situation the
brightest part of the image may be consistently coming in at only 50% of the DN. An
analog gain of 6 dB (2x) will ensure full use of the dynamic range of the A/D
converter. Of course the noise is also increased.
2. The analog offset (
60Hsao or 61Hcao command) or black level is an “artificial” offset
introduced into the video path to ensure that the A/D is functioning properly. The
analog offset should be set so that it is at least 3 times the rms noise value at the
current gain.
Digital Processing