Digital cameras that connect
to a notebook computer through the serial port or the faster USB
port have been
available for a few years. However, most of these cameras are intended for
the
consumer market,
and are equipped with cheap CMOS sensors to keep prices low. CMOS
sensors in
general have much higher dark currents than CCD sensors. In fact, the quality of
the
blue channel of
most of these cheap consumer cameras is about as bad as that obtained with
a
decent CCD
camera and a NTSC frame grabber. Nevertheless, USB cameras offer a great
low-
cost solution
for acquiring images of NTSC-like quality. However, these cameras are limited to
a
maximum
throughput of only 12 MBits/s, resulting in rather slow frame rates for images
of
decent
resolution.
IEEE-1394 Digital
Cameras
Fortunately, a
new class of digital
cameras that recently appeared on the market offers high
image quality as
well as fast frame rates. These cameras, which adopt the IEEE-1394
specifications
and communicate over the IEEE-1394 high performance serial bus, are an
ideal
solution for
acquiring high-quality images with a regular notebook computer. The fastest
IEEE-
1394 cameras
present image data at a guaranteed bandwidth of 400 MBits/s. This
bandwidth
allows the
acquisition of 30 frames per second, even at very high image
resolution.
IEEE-1394
cameras offer other advantages beyond speed. Many IEEE-1394 cameras
are
equipped with a
high-quality CCD sensor, which substantially improves the quality of the
blue
channel.
IEEE-1394 cameras are also very versatile. The user can typically choose from
several
modes of image
resolutions and from several frame rates. Moreover, all adjustable
camera
parameters can
be controlled through the IEEE-1394 link.
For our
research, we chose the DFW-V500 camera from Sony. The two photos show our
set-
up, and the
diagram illustrates the elements in it. The camera is equipped with a
high-quality 1/3"
CCD sensor with
progressive scan and square pixels. The camera supports four
resolution
modes, with a
maximum resolution of 640 x 480 in YUV (4:2:2) format. The frame rate can
be
set at 3.75,
7.5, 15, and 30 fps. Basically all camera parameters can be adjusted through
the
IEEE-1394 link:
shutter speed, gain, gamma factor, brightness, sharpness, hue, saturation,
and
white balance.
Of particular note, the shutter speed can be adjusted from very short
(1/100,000
sec) to very
long (5 sec). This camera also adopts the popular C mount optical
interface.
It is important
not to confuse IEEE-1394 digital cameras with DV (digital video)
cameras,
although both
types communicate over the fast IEEE-1394 serial link. While IEEE-1394 digital
cameras are
geared for the machine vision market, DV cameras are geared for the
consumer
market. The main
difference between the two types is image quality. DV cameras
compress
image data in
order to record longer movies onto a DV tape. Unfortunately, the
image
compression is
lossy. Although the image compression is optimized for human vision, the
image
compression
artifacts can pose serious problems for machine vision applications. In
contrast,
IEEE-1394 digital cameras do not
compress the image data, as the goal is maximum image
quality for each
individual frame, not image storage.