STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
STH-DCAM Stereo Head
User’s Manual
Updated – Rev 2
2001 Videre Design
1
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
1 Introduction
The STH-DCAM (Dual-DCAM) is a compact, low-power digital stereo
head with an IEEE 1394 digital interface. It consists of two VGA
(640x480), progressive scan CCD imagers and associated IEEE 1394
electronics, mounted in a rigid, milled Delrin frame.
The CCD imagers are Sony HAD ¼” devices, with square pixels and
progressive scan output. They have 648 H by 484 V pixels, and are
colorized using a standard Bayer pattern. These imagers have excellent
dynamic range, sensitivity, anti-blooming, and noise characteristics. They
are fully controllable via the IEEE 1394 interface, in both manual and
automatic modes. The user can set exposure, gain, binning, etc., or have
the stereo head electronics do it automatically.
The STH-DCAM uses standard 12 x 0.5 mm miniature lenses for user-
changeable optics.
Wide-angle to telephoto options are available,
depending on the application.
There are software drivers for the STH-DCAM for MS Windows
98/2000/XP, and for Linux 2.4.x kernels.
SRI’s Small Vision System (SVS) software has an interface to the STH-
DCAM. You can simply and automatically calibrate the stereo head,
perform stereo correlation, and view the results as a 3D set. The SVS
software includes all of the capture software described in this document.
3
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
2 Quick Start
The STH-DCAM comes assembled, with 3.6 mm lenses as standard.
To set up and test the STH-DCAM, you will need the following:
1. Host computer with a 1394 PCI or PCMCIA card, OHCI
compliant.
2. 1394 6-pin cable.
3. Capture software or Small Vision System installed on the host
computer.
Install the 1394 host card, if necessary, according to the directions in
Section 7.1. Install the video capture software (included with the STH-
DCAM) or Small Vision System software (see Section 7.2). This is the
not-so-quick part of the Quick Start.
The STH-DCAM has a single IEEE 1394 port, for plugging in an IEEE
1394 cable. Plug one end of a 6 pin – 6 pin IEEE 1394 cable into the port,
and the other end into any port of the host card. Note: for PCMCIA cards,
and laptops with a 4-pin Sony iLink port, an external power supply should
be plugged into the STH-DCAM to supply power to the stereo head, using
the 2.1 mm power jack. Standard IEEE 1394 PCI cards supply enough
power, and the power adapter is not necessary.
Figure 2-1 Video capture program window.
message will appear in the info window. Please see Section 7 for
troubleshooting.
To view stereo video, press the Continuous button. Left and right
images should appear in the application windows. If the message “Image
timed out” appears, then there is a problem with the IEEE 1394 drivers;
dark, should lighten as the auto exposure mode adjusts to ambient lighting
(Section 6.2). Images can be saved using the Filemenu.
Start the video capture program, smallvcap(.exe), on the host
computer. You should see a screen as in Figure 2-1. The message window
should indicate that the STH-DCAM interface is present. If not, go back to
software installation (Section 7.2), and follow the instructions for
configuring the correct capture library.
A more complete description of the video capture program is in Section 6.
The SVS programs are described in the documentation that comes with that
software. It is helpful to review Section 6 in conjunction with the SVS
documentation.
Pull down the Input chooser, and select the Videooption. If everything
has been set up, the driver software will recognize and configure the stereo
head after a few seconds, and a success message will appear in the info text
4
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
3.1 Hardware Schematic
Figure 3-2 shows the design of the internal hardware of the STH-DCAM.
In the stereo imager module, two Sony CCD imagers, each of size 648x486
pixels, digitize incoming light into a digital stream. A full frame is captured
at once, and then read out line by line. The imagers operate in progressive
3 Hardware Overview
Figure 3-1 shows the hardware configuration of the STH-DCAM.
The imager module has a milled Delrin frame that rigidly holds two Sony
mounts are attached to the frame, and standard miniature lenses are screwed
into these holders. There is an IR curoff filter, with a knee at approximately
700 nm, permanently mounted inside the lens holder. See Section 4 for
appropriate lens characteristics.
The imagers are synchronized to a common clock, so that the corresponding
pixels from each imager are output at the same time. Each imager sends out
its own video stream, on a separate IEEE 1394 cable. There are two such
cables coming out of the STH-DCAM module. Each video stream has a
maximum rate of 200 Mbps; the whole IEEE 1394 bus runs at 400 Mbps.
There is a IEEE 1394 port on the left side of the device. The cable carries
synchronized so that they are exposed at the same time, a requirement for
stereo processing whenever there is any motion (including camera motion).
Each imager is supplied with power from its cable. In order to synchronize
correctly, power must be applied to the imagers at the same time.
Typically, the two cables are connected to a small 3-port IEEE 1394 hub,
which is then connected to the host IEEE 1394 port.
Typically, the cable is plugged into the host computer IEEE 1394 card.
Power for the STH-DCAM is supplied from the card, or through a separate
power supply that plugs into the power supply port of the device (7-40
VDC).
3.2 Color and Monochrome
The Sony CCDs are color imagers, with a standard Bayer color pattern.
Processing in the STH-DCAM can produce either a color or monochrome
output from the imagers. Monochrome output is 1 byte/pixel, and color
outputs are either 2 or 3 bytes/pixel, depending on the format. If color isn’t
necessary, monochrome output should be selected, to save on movement of
data.
There are no user-settable switches on the STH-DCAM.
1394 cables
Right
miniature
3.3 Frame Rates
Left
miniature
lens
The IEEE 1394 interface supports a maximum rate of 200 Mbps on each
imager. The maximum frame rates depend on whether monochrome or
color output is used. Frame rates up to 30 Hz at 640x480 are supported.
See Table 3-1 below for a complete list of frame rates.
lens
Figure 3-1. Physical layout of the STH-DCAM stereo head.
5
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
Frame Size Frame rate,
monochrome
Frame rate,
color
Sync
signals
Left
Right
Imager
Imager
640x480
30 Hz
15 Hz
7.5 Hz
30 Hz
15 Hz
7.5 Hz
30 Hz
15 Hz
7.5 Hz
30 Hz
15 Hz
7.5 Hz
1394
imaging
commands
8-bit pixels
12 MHz per
imager
STH-DCAM
Digital Stereo
320x240
Head
1394
Interface
1394
Interface
Electronics
Electronics
Table 3-1 Supported frame rates for the STH-
DCAM, 400 Mbps IEEE 1394 bus.
Digital
Video
Stream
1394
commands
1394 Digital
Cable
Figure 3-2 Schematic of the STH-DCAM electronics.
6
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
small amount of methyl alcohol or similar lens-cleaning solvent, and wipe
the imager glass surface gently. Dry with a similar tissue.
4 Lenses
4.3 Imager Size
The STH-DCAM uses standard miniature lenses (12 x 0.5 mm). Good-
quality, fixed-focus lenses with low distortion and high light-gathering
capability are best.
The imager size is the largest size of imager that can be covered by the lens.
For the STH-DCAM, the lens must be 1/4” or larger.
Lenses are characterized optically by imager size, F number, and focal
length. Following subsections discuss the choice of these values.
4.4 F Number
The F number is a measure of the light-gathering ability of a lens. The
lower the F number, the better it is at pulling in light, and the better the
STH-DCAM will see in low-illumination settings. For indoor work, an F
number of 1.8 is acceptable, and 1.4 is even better. For outdoors, higher F
numbers are fine. Miniature lenses have no mechanical iris for exposure
adjustment. Instead, they have electronic exposure and gain control to
automatically compensate for different light conditions.
4.1 Changing Lenses
Standard miniature lenses have a 12 mm diameter, 0.5 mm pitch screw on
their back end. The screw mates with the lens holder opening. To insert a
lens, place it back end on the lens holder opening as straight as possible,
and gently turn it clockwise (looking down at the lens) until it engages the
threads of the lens holder. If you encounter a lot of resistance, you may be
cross-threading the lens. Forcing it on will damage the plastic lens holder
threads.
4.5 Focal Length
The focal length is the distance from the lens virtual viewpoint to the
imager. It defines how large an angle the imager views through the lens.
The focal length is a primary determinant of the performance of a stereo
system. It affects two important aspects of the stereo system: how wide a
field of view the system can see, and how good the range resolution of the
stereo is. Unfortunately there’s a tradeoff here. A wide-angle lens (short
focal length) gives a great field of view, but causes a drop in range
resolution. A telephoto lens (long focal length) can only see a small field of
view, but gives better range resolution. So the choice of lens focal length
usually involves a compromise. In typical situations, one usually chooses
the focal length based on the narrowest field of view acceptable for an
application, and then takes whatever range resolution comes with it.
Once the threads are engaged, continue screwing it on until most of the
thread is in the holder. Turn on the device, and check the focus, adjusting it
until there is a clear image. The depth of focus of most miniature lenses is
very large, from several inches to infinity.
Removing the lens is the reverse process: unscrew the lens counter-
clockwise.
Normal care should be used in taking care of the lenses, as with lenses for
any good-quality camera.
4.2 Cleaning the Imagers
It should not be necessary to clean the imagers, since they are sealed off by
an IR filter inside the lens mount.
If dirt and dust are present on the IR filter surface, they can be cleaned in
the same manner as a lens. Wet a non-abrasive optic cleaning tissue with a
7
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
where b is the baseline between the imagers, f is the focal length of the lens,
and ∆d is the smallest disparity the stereo system can detect. For the STH-
DCAM, b is 90 mm, and ∆d is 0.35 um (pixel size of 5.6 um, divided by
the interpolation factor of 16).
Figure 4-1 plots this relationship for several focal lengths. At any distance,
the range resolution is inversely proportional to the focal length.
4.7 Field of View
The field of view is completely determined by the focal length, given a
fixed imager. The formulas for the FOV in horizontal and vertical
directions are:
HFOV = 2arctan(1.792/ f )
VFOV = 2arctan(1.344/ f )
where f is in millimeters. For example, a 4.0 mm lens yields a horizontal
FOV of 48 degrees. The following table shows the FOV for some standard
focal lengths.
Figure 4-1 Range resolution in mm as a function of distance, for
several different lens focal lengths.
4.6 Range Resolution
Lens focal length Horizontal FOV
Vertical FOV
Range resolution is the minimum distance the stereo system can distinguish.
Since stereo is a triangulation operation, the range resolution gets worse
with increasing distance from the stereo head. The relationship is:
2.1 mm
4.0
81 deg
48
65 deg
37
r2
8.0
25
19
∆r =
∆d ,
Table 4-1 Horizontal and vertical field of view for
different lens focal lengths.
bf
8
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
PCI cards have 6-pin ports, and supply power. PCMCIA cards do not have
the capability of supplying power, and power can be supplied through the
power jack. In some cases, the PCMCIA card has an input for external
power. Plug the STH-DCAM cables into a port, and supply power through
the external input.
5 1394 Interface
Digital image information is transferred from the STH-DCAM to the host
PC via an IEEE 1394 cable. The cable sends a video stream from the
imagers to the PC, and sends commands from the PC to the stereo head to
control exposure, color balance, etc. The cable also supplies power to the
stereo head. Alternatively, power can be supplied through a separate power
jack located on the STH-DCAM.
Any 1394 card is suitable, as long as it conforms to OHCI (open host
controller interface) specifications. All current cards do, but some older
cards may not.
5.1 1394 Cable
The STH-DCAM has an IEEE 1394 port on the left side of the device.
Plug a cable from the STH-DCAM into a free port on the host controller.
The maximum length for such a cable is 4.5 m (about 15 feet). The cable
supplies both signals and power to the stereo head; alternatively, power can
be supplied at the device using a separate power supply.
The distance between the stereo head and the PC can be extended by using
an IEEE 1394 repeater.
Several 1394-enabled devices can be connected together, as long as the
connection topology doesn’t have any loops. The STH-DCAM is always a
leaf of the bus. At a maximum, it will need about 60% of the bandwidth of
a 400 MBps connection.
5.2 1394 Host Interface
The host computer must have an available 1394 port. Some portables and
desktops come with built-in ports. If these are 6-pin ports, they can be
connected directly to the STH-DCAM. Sony laptops also support an
alternative 4-pin 1394 cabling, which has the signal pins but no power. Use
a 4-pin to 6-pin cable on these ports, and supply power to the STH-DCAM
using the separate power port.
If the host PC doesn’t have a built-in 1394 port, one can be added by
installing an IEEE 1394 PCI card or PCMCIA card for laptops. IEEE 1394
9
2001 VIDERE DESIGN
monochrome channels and one RGB color channel. The color channel
corresponds to the left image, which is the reference image for stereo. The
color image can be de-warped, just like the monochrome image, to take into
account lens distortion (see the Small Vision System User’s Manual).
6 User Controls
The CCD imagers are fully controllable via the IEEE 1394 interface. User
programs may input color images, set video digitization parameters
(exposure, gain, red and blue balance), and frame size. All of these
parameters can be set with the included capture application, or with the SRI
Small Vision System. They are also accessible to user programs through
the capture API (Section 8).
Color information from the camera is input only if the Colorbuttons are
pressed on the main window (Figure 2-1). Color/monochrome can only be
changed while the STH-DCAM is not outputting images.
Because the typical color camera uses a colorizing filter on top of its pixels,
the color information is sampled at a lower resolution than a similar non-
colorized camera samples monochrome information. In general, a color
camera has about ¼ the spatial resolution of a similar monochrome camera.
To compensate for the reduced resolution, use binning (Section 6.3) to
increase the fidelity of the image. For example, if you need a 320x240
frame size, use 640x480 and binning x2.
User controls for frame size and sampling modes are on the main capture
window dialog. Video digitization and Subwindowing controls are
accessed through a dialog invoked with the Video… menu item. Figure 6-1
shows the dialog.
The relative amounts of the three colors, red/green/blue, affects the
appearance of the color image. The STH-DCAM CCD imagers have
attached processors that automatically balance the offsets among these
colors, to produce an image that is overall neutral (called white balance).
Alternatively, the application program can control the color balance
manually. Manual balance is useful in many machine vision applications,
because automatic white balance continuously changes the relative amount
of color in the image.
6.1 Color
Color information from the STH-DCAM digital head is input as raw
colorized pixels, and converted by the interface library into two
The manual gain on red and blue pixels is adjusted using the Red and Blue
controls on the Video Parameters dialog. For a particular lighting source,
try adjusting the gains until a white area in the scene looks white, without
any color bias.
6.2 Video Digitization Parameters
The CCD imagers have electronic exposure and gain controls to
compensate for varying lighting conditions. The exposure can vary from a
maximum of a full frame time to a minimum of one line time. Gain is an
additional amplification of the video signal, for low-light situations. It is
settable from 0 to 18 dB.
Figure 6-1 Video Parameters dialog.
10
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
Both imagers are treated in exactly the same manner. It is not possible to
set a different exposure or gain on each imager.
Digitization control can operate in either manual or automatic mode. Refer
to Figure 6-1 for the controls in the video capture program.
In manual mode, the user program sets the exposure and gain. The
exposure and gain are based on a 0 to 100 scale. Here are some tips for
setting exposure and gain.
•
In general, keep the gain as low as possible, since it introduces
additional noise into the system. Use it only if the exposure is set
to maximum, or if the exposure must be kept low to minimize
motion blur.
•
Adjust the manual iris of the lens to as small an opening as
possible for your application, without having to use gain. This
will increase the depth of field and give better optical performance.
6.3 Subsampling
In many applications it is not necessary to work with the the full 640x320
pixel array. The CCD image processors are capable of reducing the amount
of information contained in the digital video stream sent back to the host.
They do this by averaging the values from neighboring pixels, giving a
higher signal-to-noise ration. This technique is called binning. Binning
occurs automatically when a smaller frame size is selected.
Figure 6-2 Frame size control in the main capture window.
6.5 Frame Rates
Frame rates from the STH-DCAM depend on the frame size and color
mode. Frame rates can be set under program control with the SetRate()
function; see the Small Vision System User’s Manual. For the smallv
and smallvcapapplications, frame rates are set at 30 Hz.
Figure 6-2 shows the frame size control on the video capture application.
The two frame sizes allowed are 640x480 (full frame) and 320x240 (x2
binning).
6.4 Subwindowing
Monochrome
30, 15, 7.5
30, 15, 7.5
Color
Frame Rates, Hz
320x240
The STH-DCAMs do not support subwindowing..
30, 15, 7.5
30, 15, 7.5
640x480
Table 6-1 Allowable frame rates for the STH-DCAM in different
modes.
11
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
7.2.1 MS Windows Installation
To install the software under MS Windows, execute the file
svscap22X.exe. The installation process will add the relevant interface
and application software.
7 Installing the 1394 Host Card and Capture
Software
The STH-DCAM connects to a host computer via a digital 1394 interface.
The host PC must have a 1394 port, and software to interface to the video
stream from the camera. This interface software presents the video stream
from the 1394 hardware as a set of stereo frames to the user program (see
Figure 7-1). The STH-DCAM comes with interface software for either MS
Windows 98/2000 or Linux.
The directory structure for the software is:
bin\
smallvcap.exe
stcap.exe
svsgrab.dll, .lib
dcamcap.dll, .lib
src\
svs.h
svsclass.h
samples\
7.1 1394 Hardware and Drivers
Before installing the software interface, the PC must be equipped with a
1394 port. If there is one already present, on the motherboard, then you can
skip this section. Otherwise you have to install a PCI or PCMCIA card.
The card must be OHCI compliant, which all current cards are.
*.cpp
*.dsp, samples.dsw
There are two applications. smallvcap.exeis a GUI-based application
that allows the user to exercise the capture functions of the STH-DCAM. It
is described in earlier sections of this document.
Please see the Videre Design website (www.videredesign.com/support.htm)
for the latest information about installing hardware and software drivers.
After installing the card, install the STH-DCAM driver software.
stcap.exe is a simple application that connects to the stereo head and
displays stereo images. It can serve as a template for user programs that
integrate stereo capture from the STH-DCAM.
7.2 STH-DCAM Software
libcap.dllis the capture library for Linux. These libraries must be set
to the correct ones for the STH-DCAM. Copy the following files in the
bin\directory:
The STH-DCAM comes with interface software and several sample
applications, including the capture application described in this manual.
svsdcam.dll -> svsgrab.dll
svsdcam.lib -> svsgrab.lib
1394
video
stream
To
user
program
You can check that the correct interface library is installed, by looking at
the information text when the capture application is started. It should say
“Dual DCAM digital stereo interface”. If not, the wrong interface library is
installed in svsgrab.dll.
1394
PC
Hardware
Low-level
1394
driver
STH-MD1
interface
software
Figure 7-1 Host PC low-level software structure.
12
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
7.2.2 Linux Installation
To install the software under Linux, untar the file svscap22X.tgzin a
new directory, which will become the top-level directory of the software.
Add bin/to your LD_LIBRARY_PATH variable.
The directory structure for the software is:
bin/
smallvcap
stcap
libsvscap.so
pixcap.so
dcamcap.so
src/
svs.h
svsclass.h
samples/
*.cpp
makefile
There are two applications. smallvcapis a GUI-based application that
allows the user to exercise the capture functions of the STH-DCAM. It is
described in earlier sections of this document.
stcapis a simple application that connects to the stereo head and displays
stereo images. It can serve as a template for user programs that integrate
stereo capture from the STH-DCAM.
libsvscap.sois the capture library for Linux. These libraries must be
set to the correct ones for the STH-DCAM. Copy the following files in the
bin/ directory:
dcamcap.so -> libsvscap.so
You can check that the correct interface library is installed, by looking at
the information text when the capture application is started. It should say
“Dual DCAM digital stereo interface”. If not, the wrong interface library is
installed in libsvscap.so.
13
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
Color, 8 bits / pixel, Bayer pattern
Scan mode
Progressive
Pixel size
5.6 um square
Sensitivity
1 lux
Exposure
9 Technical Specifications
9.1 Geometry
Housing
Rigid milled Delrin frame
Baseline
9 cm, fixed
Electronic, 292 us to frame time
Imager size
Gain
1/4 inch diagonal
18 dB
Lens type
Resolution
640 H x 480 V
12 mm miniature, interchangeable
9.2
Interface
9.4
Frame formats and rates
Type
Monochrome, 640x480 and 320x240
RGB Color, 640x480 and 320x240
30, 15, 7.5 Hz
Digital 1394 [Firewire], OHCI compliant
Speed
Maximum 20 megapixels / second
Host interface
Any 1394 OHCI card
RGB 640x480 at 15 and 7.5 Hz only
Host OS
Windows 98 / 2000 / XP, Linux
9.5
Physical
Power
2 watts
9.3
Imagers
Ports
Type
One IEEE 1394 port (power and signal)
One power jack (7-40 VDC, 2W)
Sony Wfine HAD CCD
Format
15
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
Stereo module size
6" x 2.6" x 1"
Weight (with lenses)
8 ounces
16
STH-DCAM USER’S MANUAL
2001 VIDERE DESIGN
10 Technical Support
For technical support, please contact Videre Design by email or FAX.
Videre Design
P.O. Box 585
Menlo Park, CA 94026-0585
Fax: (650)323-3646
Email: [email protected]
Technical information about stereo algorithms and stereo calibration can be
17
|