Proxima ASA STH-MD1/-C - Manual (Page 6)

STH-MD1 U SER ’ S M ANUAL
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2001 V IDERE D ESIGN
6
3 Hardware Overview
Figure 3-1 shows the hardware configuration of the STH-MD1/-C.
The imager module has a milled Delrin frame that rigidly holds two
megapixel imagers, separated by a fixed distance of 9 cm. Lens mounts
are an integral part of the frame, and standard C-mount lenses are screwed
into these holders. There is an IR cutoff filter, with a knee at
approximately 700 nm, permanently mounted inside the lens holder. See
Section 4 for appropriate lens characteristics.
The interface module is mounted on the back of the stereo head. Two 1394
ports are placed at the top of the module. Either port can be used as a
connection to the host PC. The two ports allow daisy-chaining of the 1394
cable to other devices. Use only one port to connect the STH-MD1/-C to
the host computer!
A status LED indicates video imager activity. It will flash at half the frame
rate. It should begin flashing as soon as power is supplied to the camera
through the IEEE 1394 cable, since the imagers are always active, even
when images are not being acquired by the host computer. Changing the
video modes (frame size, decimation) will cause the frame rate to change,
and this will be reflected in the LED flash rate.
There are no user-settable switches on the STH-MD1/-C.
3.1 Hardware Schematic
Figure 3-2 shows the design of the internal hardware of the STH-MD1/-C.
In the stereo imager module, two CMOS imagers, each of size 1288 x 1032
pixels, digitize incoming light into a digital stream. The imagers operate
in progressive mode only, that is, each line is output in succession from the
full frame.
The maximum video rate is 12 megapixels per second from each imager.
The imagers are synchronized to a common clock, so that the
corresponding pixels from each imager are output at precisely the same
time. Special interlace electronics convert the individual streams into a
single pixel-interlaced stream at 24 MHz. The interlaced stream contains
one byte from the left imager, then the corresponding byte from the right
imager, then the next byte from the right imager, and so on.
The interlaced video stream is transferred to the 1394 interface module,
which communicates to the host PC over a 1394 digital cable. The module
also accepts commands from the host PC over the cable, and uses these
commands to control imaging modes such as exposure or subwindowing.
The 1394 interface module can communicate at the maximum 1394 data
rate, 400 MBps.
3.2 Frame Rates
The 1394 interface electronics supports a maximum rate of 24 megapixels
per second. At this rate, there is no need for large buffer memories to hold
video data on the stereo device. At maximum frame size, the frame rate is
7.5 frames per second. Subsampling modes support higher frame rates,
from 26 fps at 640 x 480 to 110 fps at 320 x 240 (Section 6.8).
Figure 3-1. Physical layout of the STH-MD1/-C stereo head.
Left
C-mount
lens
1394 ports
Right
C-mount
lens
LED
indicator