ServSwitch Agility Dual with VNC
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Ignore Dithering
Dithering is a technique used by some graphics cards
to improve perceived image quality by continuously
slightly varying the colour of each pixel. This gives the
illusion of more shades of colour than the display can
really reproduce, and smooths the appearance of
gradually shaded areas in images. Unfortunately, dith-
ering is an issue for KVM extenders because it makes
the image appear to be changing all the time even
when it is static. This means that a great deal of
unnecessary network data is sent to the VNC viewer,
reducing the video frame rate and making mouse
response appear slow.
The ‘Ignore Dithering’ option works by ignoring small
variations in the video from frame to frame. This
increases performance and reduces network traffic
when the host computer is an Apple Mac or another
computer that has dithered video output. It also
improves performance if the video source is noisy (e.g.
from a camera or a VGA-to-DVI converter). ‘Ignore
Dithering’ is disabled by default to give full colour
accuracy and the best possible frame rate from non-
dithered video sources.
4.10 Video settings
This option provides a range of options related to the video configuration.
Video source
Selects which video input to use. It is
possible to display both single head
screens (if connected) or select one over
the other. If you are viewing Dual-Link
video resolutions, only one head will be
available.
Use Remote DDC
Uses the DDC of the monitors connect-
ed to the Agility Reciever. If this option
is un-ticked you can select a DDC to use
that is reported by the Agility Dual with
VNC.
Hot Plug Detect
When ticked, allows you to choose one
of four hot plug detect periods when,
after a display is connected, the DDC
information is sought.
Threshold
Adjusts the level of dithering noise that is
ignored. The ‘Auto’ button attempts to
choose a suitable value automatically, but
the level can also be adjusted manually using
the slider or arrow buttons. The best value is
of course a compromise between capturing
all the ‘real’ screen changes whilst ignoring
the (almost invisible) dithering noise. A good
way to choose the value is to watch the
Display Activity indicator for a static screen.
If the Threshold is too low, the Display
Activity will be a high percentage while
nothing is really changing. If the Threshold is
too high, the Display Activity will be very low
(or zero) but some real changes in the screen
may be missed.
