The
basic structure of FireWire cameras is based on the following six modules:
Optics FireWire
cameras are based on
CCD or
CMOS chips. The light-sensitive area, as well as the
pixels of these chips, are small. In the case of cameras with integrated
optics, we can assume that the optics are adapted to these chips. However, in the domains of
professional, and semi-professional
photography, as well as in the domain of
special cameras, interchangeable optics are often used. In these cases, a system specialist has to adapt the optics and the chip to the application (see
System integration). Besides normal
lenses, such interchangeable lenses may be
microscopes,
endoscopes,
telescopes, etc. With the exception of the standard C-mount and CS-mount, the mounts of interchangeable optics are company-specific.
Signal capture Since the function of a FireWire camera depends upon electrical signals, the module "signal capture" transforms the incident
light, as well as the incident
sound into
electrons. In the case of light, this process is performed by a CCD or CMOS chip. The transformation of the sound is performed by a
microphone.
Digitization The first step of the image's
digitization results from the structure of a CCD or CMOS chip. It dissects the image into pixels. If a pixel has collected many photons, it creates a high voltage. Should there only be a few photons, a low voltage is created. "Voltage" is an analog value. Therefore, during the digitization's second step, the voltage has to be transformed into a digital value by an
A/D converter. Now the raw digital image is available. A microphone transforms the sound into a voltage. An A/D converter transforms these analog values into digital ones.
Signal enhancement The creation of
color is based on a color filter, which is located in front of the CCD or CMOS chip. It is
red,
green or
blue and changes its color from pixel to pixel. Therefore, the filter is called a
color filter array or, after its inventor,
Bayer filter. Using these raw
digital images, the module "signal enhancement" creates an image, which meets aesthetic
requirements. The same is true for the audio data. In the final step, the module compresses the image and audio data and outputs them - in the case of video cameras - as a
DV data stream. In the case of
photo cameras, single images may be output and, if applicable, voice comments as files. The application
domains of industry, medicine, astronomy, microscopy and science often use special
monochrome cameras. They forgo any
signal enhancement and thus output the digital image
data in its raw state. Some special models of color cameras are only capable of outputting raw digital image data. Such cameras are called ColorRAW or Bayer cameras. They are often used in industry, medicine, astronomy, microscopy, and science. In form of photo cameras, they are used by professional photographers. Semi-professional photo cameras often offer an optional
RAW mode. The enhancement of the raw digital data takes place outside the camera on a computer and therefore the user is able to adapt it to a particular application.
Interface The first three modules are part of any digital camera. The
interface is the module that characterizes the FireWire camera. It is based on the IEEE 1283 standard, defined by the organization "Institute of Electrical and Electronics Engineers". This standard defines a
bus, which transmits: • time critical data, for example, a video and • data whose integrity is of critical importance (for example, parameters or files). It allows the simultaneous use of up to 74 different devices (
cameras,
scanners,
video recorders,
hard disks,
DVD drives, etc.). Other standards, called "
protocols" define the behavior of these devices. FireWire cameras mostly use one of the following protocols: ; AV/C : AV/C stands for "Audio Video Control" and defines the behavior of DV devices, for example, video cameras and video recorders. It is a standard, defined by the 1348 Trade Association. The Audio/Video Working Group is in charge of it. ; DCAM : DCAM stands for "1394-based Digital Camera Specification" and defines the behavior of cameras that output uncompressed image data without audio. It is a standard, defined by the 1394 Trade Association. The IIDC (Instrumentation and Industrial Control Working Group) is in charge of it. ; IIDC :
IIDC is often used synonymously with DCAM. ; SBP-2 : SBP-2 stands for "Serial Bus Protocol" and defines the behavior of mass storage devices, such as hard disks. It is an
ANSI standard maintained by
NCITS. Devices that use the same protocol are able to communicate with each other. A typical example is the connection of a video camera and a video recorder. Thus, in contrast to the USB bus, there is no need to use a controlling computer. If a computer is used, it has to be compatible with the protocols of the device with which it is to communicate (please cf.
Exchanging data with computers).
Control The controlling module coordinates the other ones. The user may specify its behavior by: • switches outside the camera, • the FireWire bus, using
application software or • a hybrid of the first two cases. ==Photo cameras==