FireWire camera
Encyclopedia
FireWire cameras use the IEEE 1394 bus
standard
for the transmission
of audio
, video
and control data. FireWire is Apple Computer
's trademark
for the IEEE 1394 standard.
FireWire camera
s are available in the form of photo camera
s and video camera
s, which provide image
and audio
data
. A special form of video
camera
s is used in the domains of industry
, medicine
, astronomy
, microscopy
and science
. These special camera
s do not provide audio data.
s are based on CCD
or CMOS
chips. The light sensitive area, as well as the pixel
s of these chips are small. In the case of cameras with integrated optics
we can assume that the optics is 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 microscope
s, endoscopes, telescope
s, etc. With the exception of the standard C-mount and CS-mount, the mounts of interchangeable optics are company-specific.
, as well as the incident sound
into electron
s. 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
.
. 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.
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
image
s, the module "signal enhancement" creates an image, which meets aesthetic requirement
s. 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 camera 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.
is the module that characterizes the FireWire camera. It is based on the IEEE 1394 standard, defined by the organization "Institute of Electrical and Electronics Engineers". This standard defines a bus
, which transmits:
It allows the simultaneous use of up to 63 different devices (camera
s, scanner
s, video recorder
s, hard disk
s, 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 1394 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).
s, offer FireWire interfaces to transfer image data and to control the camera.
The image data's transfer is based on the protocol SBP-2. In this mode, the camera behaves as an external hard disk and thus enables the simple exchange of image files with a computer (please cf. Exchanging data with computers).
To increase the work efficiency in a photo studio, additionally photo cameras and digital backs are controllable via the FireWire bus. Usually the camera manufacturer does not publish the protocol used in this mode. Therefore, camera control requires a specialized piece of software provided by the camera manufacturer, which mostly is available for Macintosh and Windows
computers.
The majority of video cameras only provides the output of audio and video data via the FireWire bus ("DVout"). Additionally, some video cameras are able to record audio and video data ("DVout/DVin"). Video cameras exchange their data with computers and/or video recorders.
Due to their field of application, their behavior is considerably different from photo cameras or video cameras:
In comparison to photo or video cameras, these special cameras are very simple. However, it makes no sense to use them in an isolated manner. They are, as other sensors, only components of a bigger system (please cf. System integration).
If the camera is to communicate with a computer, this computer has to have a FireWire interface and to use the camera's protocol. The old days of FireWire cameras were dominated by company specific solutions. Some specialist offered interface boards and driver
s, which were accessible only by their application software. Following this approach, application software is in charge of the protocol. Since this solution utilizes the computing resources in a very efficient manner, it is still used in the context of highly specialized, industrial projects. This strategy often leads to problems, using other FireWire devices, as for instance hard disks. Open systems avoid this disadvantage.
Open systems are based on a layer model
. The behavior of the single layers (interface board, low level driver, high level driver and API
) follows the constraints of the respective operating system manufacturer. Application software is allowed to access operating system APIs, but never should access any level lower. In the context of FireWire cameras, the high level drivers are responsible for the protocol. The low level drivers and the interface boards put the definitions of the standard IEEE 1394 into effect. The advantage of this strategy is the simple realization of application software, which is independent of hardware and specific manufacturers.
Especially in the domains of photo cameras and special cameras hybrids between open and company specific systems are used. The interface boards and the low level drivers typically adhere to the standard, while the levels above are company specific.
The basic characteristic of open systems is not to use the APIs of the hardware manufacturers, but those of the operating system. For Apple and Microsoft the subject "image and sound" is of high importance. According to their APIs - QuickTime
and DirectX
- are very well known. However, in the public perception they are reduced to the reproduction of audio and video. Actually, they are powerful APIs that are also responsible for image acquisition.
Under Linux this API is called video4linux. It is less powerful than QuickTime and DirectX and therefore additional APIs exist besides video4linux:
Photo cameras : Photo cameras usually use Linux' infrastructure for mass storage devices. One of the typical applications is digiKam.
Video cameras : Video cameras are accessed by various APIs. The image to the right depicts the access of the video editing software Kino to the libavc1394 API. Kino also accesses other APIs which are not shown in the image to simplify matters.
Special cameras : The most important API for special cameras is libdc1394. The image to the right depicts the access of the application software Coriander to this API. Coriander controls FireWire cameras that are based on the protocol DCAM (IIDC) and acquires their images.
In order to simplify the use of video4linux and the dedicated APIs, the meta API unicap has been developed. It covers their bits and pieces with the aid of a simple programming model.
Many aspects of system integration are not directly related to FireWire cameras. For example, illumination
has a very strong influent on the quality of the acquired images. This holds true for both aesthetic and analytical applications.
However, in the context of the realization of application software, there is a special feature, which is typical for FireWire cameras. It is the availability of standardized protocols, such as AV/C, DCAM, IIDC and SBP-2 (please cf. Structure / Interface and Exchanging data with computers). Using these protocols, the software is written independently from any particular camera and manufacturer.
By leaving the realization of the protocol to the operating system, and by enabling access to a set of APIs, software can be developed independently from hardware. If, for instance, under Linux a piece of application software uses the API libdc1394 (please cf. Exchanging data with computers), it can access all FireWire cameras that use the protocol DCAM (IIDC). Using the API unicap additionally permits access to other video sources, such as frame grabbers.
Bus
A bus is a road vehicle designed to carry passengers. Buses can have a capacity as high as 300 passengers. The most common type of bus is the single-decker bus, with larger loads carried by double-decker buses and articulated buses, and smaller loads carried by midibuses and minibuses; coaches are...
standard
Standards organization
A standards organization, standards body, standards developing organization , or standards setting organization is any organization whose primary activities are developing, coordinating, promulgating, revising, amending, reissuing, interpreting, or otherwise producing technical standards that are...
for the transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
of audio
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
, video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
and control data. FireWire is Apple Computer
Apple Computer
Apple Inc. is an American multinational corporation that designs and markets consumer electronics, computer software, and personal computers. The company's best-known hardware products include the Macintosh line of computers, the iPod, the iPhone and the iPad...
's trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...
for the IEEE 1394 standard.
FireWire camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
s are available in the form of photo camera
Digital camera
A digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
s and video camera
Video camera
A video camera is a camera used for electronic motion picture acquisition, initially developed by the television industry but now common in other applications as well. The earliest video cameras were those of John Logie Baird, based on the electromechanical Nipkow disk and used by the BBC in...
s, which provide image
Image
An image is an artifact, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person.-Characteristics:...
and audio
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
. A special form of video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...
camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
s is used in the domains of industry
Industry
Industry refers to the production of an economic good or service within an economy.-Industrial sectors:There are four key industrial economic sectors: the primary sector, largely raw material extraction industries such as mining and farming; the secondary sector, involving refining, construction,...
, medicine
Medicine
Medicine is the science and art of healing. It encompasses a variety of health care practices evolved to maintain and restore health by the prevention and treatment of illness....
, astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, microscopy
Microscopy
Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye...
and science
Science
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...
. These special camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
s do not provide audio data.
Structure
The basic structure of FireWire cameras is based on the following six modules:Optics
FireWire cameraCamera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
s are based on CCD
Charge-coupled device
A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...
or CMOS
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
chips. The light sensitive area, as well as the pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
s of these chips are small. In the case of cameras with integrated optics
Optics
Optics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
we can assume that the optics is adapted to these chips.
However, in the domains of professional
Professional
A professional is a person who is paid to undertake a specialised set of tasks and to complete them for a fee. The traditional professions were doctors, lawyers, clergymen, and commissioned military officers. Today, the term is applied to estate agents, surveyors , environmental scientists,...
and semi-professional photography
Photography
Photography is the art, science and practice of creating durable images by recording light or other electromagnetic radiation, either electronically by means of an image sensor or chemically by means of a light-sensitive material such as photographic film...
, as well as in the domain of special
Special
Special or specials may refer to:In music:* "Special" * "Special" * "Special" * The Specials, a British bandIn film and television:...
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
Photographic lens
A camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...
, such interchangeable lenses may be microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
s, endoscopes, telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
s, 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 lightLight
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
, as well as the incident sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...
into electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s. 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
Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...
.
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 converterAnalog-to-digital converter
An analog-to-digital converter is a device that converts a continuous quantity to a discrete time digital representation. An ADC may also provide an isolated measurement...
. 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 colorColor
Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light interacting in the eye with the spectral sensitivities of the light receptors...
is based on a color filter, which is located in front of the CCD or CMOS chip. It is red
Red
Red is any of a number of similar colors evoked by light consisting predominantly of the longest wavelengths of light discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths than this are called infrared , and cannot be seen by the naked eye...
, green
Green
Green is a color, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 520–570 nanometres. In the subtractive color system, it is not a primary color, but is created out of a mixture of yellow and blue, or yellow and cyan; it is considered...
or blue
Blue
Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal...
and changes its color from pixel to pixel. Therefore, the filter is called a color filter array
Color filter array
In photography, a color filter array , or color filter mosaic , is a mosaic of tiny color filters placed over the pixel sensors of an image sensor to capture color information....
or, after its inventor, Bayer filter
Bayer filter
A Bayer filter mosaic is a color filter array for arranging RGB color filters on a square grid of photosensors. Its particular arrangement of color filters is used in most single-chip digital image sensors used in digital cameras, camcorders, and scanners to create a color image...
. Using these raw digital
Digital
A digital system is a data technology that uses discrete values. By contrast, non-digital systems use a continuous range of values to represent information...
image
Image
An image is an artifact, for example a two-dimensional picture, that has a similar appearance to some subject—usually a physical object or a person.-Characteristics:...
s, the module "signal enhancement" creates an image, which meets aesthetic requirement
Requirement
In engineering, a requirement is a singular documented physical and functional need that a particular product or service must be or perform. It is most commonly used in a formal sense in systems engineering, software engineering, or enterprise engineering...
s. 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
Digital video
Digital video is a type of digital recording system that works by using a digital rather than an analog video signal.The terms camera, video camera, and camcorder are used interchangeably in this article.- History :...
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
Monochrome
Monochrome describes paintings, drawings, design, or photographs in one color or shades of one color. A monochromatic object or image has colors in shades of limited colors or hues. Images using only shades of grey are called grayscale or black-and-white...
cameras. They forgo any signal enhancement and thus output the digital image data
Data
The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...
in its raw state.
Some special models of color camera 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
RAW image format
A camera raw image file contains minimally processed data from the image sensor of either a digital camera, image scanner, or motion picture film scanner. Raw files are so named because they are not yet processed and therefore are not ready to be printed or edited with a bitmap graphics editor...
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 interfaceElectrical connector
An electrical connector is an electro-mechanical device for joining electrical circuits as an interface using a mechanical assembly. The connection may be temporary, as for portable equipment, require a tool for assembly and removal, or serve as a permanent electrical joint between two wires or...
is the module that characterizes the FireWire camera. It is based on the IEEE 1394 standard, defined by the organization "Institute of Electrical and Electronics Engineers". This standard defines a bus
Computer bus
In computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
, 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 63 different devices (camera
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
s, scanner
Image scanner
In computing, an image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop scanner where the document is placed on a glass...
s, video recorder
Digital video recorder
A digital video recorder , sometimes referred to by the merchandising term personal video recorder , is a consumer electronics device or application software that records video in a digital format to a disk drive, USB flash drive, SD memory card or other local or networked mass storage device...
s, hard disk
Hard disk
A hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
s, DVD
DVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
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 1394 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
Ansi
Ansi is a village in Kaarma Parish, Saare County, on the island of Saaremaa, Estonia....
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 softwareApplication softwareApplication software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...
or - a hybrid of the first two cases.
Photo cameras
Professional and semi-professional photo cameras, and especially digital camera backDigital camera back
A digital camera back is a device that attaches to the back of a camera in place of a film holder and contains an electronic image sensor. This lets cameras that were designed to use film take digital photographs...
s, offer FireWire interfaces to transfer image data and to control the camera.
The image data's transfer is based on the protocol SBP-2. In this mode, the camera behaves as an external hard disk and thus enables the simple exchange of image files with a computer (please cf. Exchanging data with computers).
To increase the work efficiency in a photo studio, additionally photo cameras and digital backs are controllable via the FireWire bus. Usually the camera manufacturer does not publish the protocol used in this mode. Therefore, camera control requires a specialized piece of software provided by the camera manufacturer, which mostly is available for Macintosh and Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
computers.
Video cameras
Although compatibility to the FireWire bus is only found in high-end photo cameras, it has usually been present in home-user level video cameras. Video cameras are mostly based on the protocol AV/C. It defines the flow of audio and video data, as well as the camera's control signals.The majority of video cameras only provides the output of audio and video data via the FireWire bus ("DVout"). Additionally, some video cameras are able to record audio and video data ("DVout/DVin"). Video cameras exchange their data with computers and/or video recorders.
Special cameras
In the domains of industry, medicine, astronomy, microscopy and science FireWire cameras are often used not for aesthetic, but rather for analytical purposes. They output uncompressed image data, without audio. These cameras are based on the protocol DCAM (IIDC) or on company specific protocols.Due to their field of application, their behavior is considerably different from photo cameras or video cameras:
- Their case is small and built mainly from metal and do not follow aesthetic, but rather functional design constraints.
- The vast majority of special cameras does not offer integrated optics, but a standardized lens mount called "C-mount" or "CS-mount". This standard is not only used by lenses, but also by microscopes, telescopes, endoscopes and other optical devices.
- Recording aids, such as autofocusAutofocusAn autofocus optical system uses a sensor, a control system and a motor to focus fully automatic or on a manually selected point or area. An electronic rangefinder has a display instead of the motor; the adjustment of the optical system has to be done manually until indication...
or image stabilization are not available. - Special cameras often utilize monochrome CCD or CMOS chips.
- Special cameras often do not apply an infrared cut filter or optical low pass filters, thus avoid affecting the image.
- Special cameras output image data streams and single images, which are captured using an external trigger signal. In this way, these cameras can be integrated into industrial processes.
- Mass storageMass storageIn computing, mass storage refers to the storage of large amounts of data in a persisting and machine-readable fashion. Devices and/or systems that have been described as mass storage include tape libraries, RAID systems, hard disk drives, magnetic tape drives, optical disc drives, magneto-optical...
devices are not available since the images have to be analyzed more or less immediately by the computer connected to the camera. - The vast majority of special cameras is controlled by application software, installed on a computer. Therefore, the cameras do not have external switches.
- Application software is rarely available off-the-shelf. It usually has to be adapted to the specific application. Therefore, camera manufacturers offer programming tools designed for their cameras. If a camera uses the standard protocol DCAM (IIDC), it can also be used with third party software. A lot of industrial computers and embedded systemEmbedded systemAn embedded system is a computer system designed for specific control functions within a larger system. often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal...
s are compatible to the DCAM (IIDC) protocol (please cf. Structure / Interface and Exchanging data with computers).
In comparison to photo or video cameras, these special cameras are very simple. However, it makes no sense to use them in an isolated manner. They are, as other sensors, only components of a bigger system (please cf. System integration).
Exchanging data with computers
FireWire cameras are able to exchange data with any other FireWire device, as long as both devices use the same protocol (please cf. Structure / Interface). Depending upon the specific camera, these data are:- Image and audio files (protocol: SBP-2)
- Image and audio data flows (protocol: AV/C or DCAM (IIDC))
- Parameters to control the camera (protocol: AV/C or DCAM (IIDC))
If the camera is to communicate with a computer, this computer has to have a FireWire interface and to use the camera's protocol. The old days of FireWire cameras were dominated by company specific solutions. Some specialist offered interface boards and driver
Device driver
In computing, a device driver or software driver is a computer program allowing higher-level computer programs to interact with a hardware device....
s, which were accessible only by their application software. Following this approach, application software is in charge of the protocol. Since this solution utilizes the computing resources in a very efficient manner, it is still used in the context of highly specialized, industrial projects. This strategy often leads to problems, using other FireWire devices, as for instance hard disks. Open systems avoid this disadvantage.
Open systems are based on a layer model
OSI model
The Open Systems Interconnection model is a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a prescription of characterizing and standardizing the functions of a communications system in terms of abstraction layers. Similar...
. The behavior of the single layers (interface board, low level driver, high level driver and API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
) follows the constraints of the respective operating system manufacturer. Application software is allowed to access operating system APIs, but never should access any level lower. In the context of FireWire cameras, the high level drivers are responsible for the protocol. The low level drivers and the interface boards put the definitions of the standard IEEE 1394 into effect. The advantage of this strategy is the simple realization of application software, which is independent of hardware and specific manufacturers.
Especially in the domains of photo cameras and special cameras hybrids between open and company specific systems are used. The interface boards and the low level drivers typically adhere to the standard, while the levels above are company specific.
The basic characteristic of open systems is not to use the APIs of the hardware manufacturers, but those of the operating system. For Apple and Microsoft the subject "image and sound" is of high importance. According to their APIs - QuickTime
QuickTime
QuickTime is an extensible proprietary multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. The classic version of QuickTime is available for Windows XP and later, as well as Mac OS X Leopard and...
and DirectX
DirectX
Microsoft DirectX is a collection of application programming interfaces for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with Direct, such as Direct3D, DirectDraw, DirectMusic, DirectPlay,...
- are very well known. However, in the public perception they are reduced to the reproduction of audio and video. Actually, they are powerful APIs that are also responsible for image acquisition.
Under Linux this API is called video4linux. It is less powerful than QuickTime and DirectX and therefore additional APIs exist besides video4linux:
Photo cameras : Photo cameras usually use Linux' infrastructure for mass storage devices. One of the typical applications is digiKam.
Video cameras : Video cameras are accessed by various APIs. The image to the right depicts the access of the video editing software Kino to the libavc1394 API. Kino also accesses other APIs which are not shown in the image to simplify matters.
Special cameras : The most important API for special cameras is libdc1394. The image to the right depicts the access of the application software Coriander to this API. Coriander controls FireWire cameras that are based on the protocol DCAM (IIDC) and acquires their images.
In order to simplify the use of video4linux and the dedicated APIs, the meta API unicap has been developed. It covers their bits and pieces with the aid of a simple programming model.
System integration
Often FireWire cameras are only a cog in a bigger system. Typically, a system specialist uses a number of different components to solve a particular problem. There are two basic approaches to do this:- The problem at hand is interesting enough for a group of users. The typical indicator of this situation is the off-the-shelf availability of application software. Studio photography is an example.
- The problem at hand is only of interest to a particular application. In such cases, there is typically no application software available off-the-shelf. Therefore, it has to be written by a system specialist. The gauging of a steel plate is an example.
Many aspects of system integration are not directly related to FireWire cameras. For example, illumination
Lighting
Lighting or illumination is the deliberate application of light to achieve some practical or aesthetic effect. Lighting includes the use of both artificial light sources such as lamps and light fixtures, as well as natural illumination by capturing daylight...
has a very strong influent on the quality of the acquired images. This holds true for both aesthetic and analytical applications.
However, in the context of the realization of application software, there is a special feature, which is typical for FireWire cameras. It is the availability of standardized protocols, such as AV/C, DCAM, IIDC and SBP-2 (please cf. Structure / Interface and Exchanging data with computers). Using these protocols, the software is written independently from any particular camera and manufacturer.
By leaving the realization of the protocol to the operating system, and by enabling access to a set of APIs, software can be developed independently from hardware. If, for instance, under Linux a piece of application software uses the API libdc1394 (please cf. Exchanging data with computers), it can access all FireWire cameras that use the protocol DCAM (IIDC). Using the API unicap additionally permits access to other video sources, such as frame grabbers.
See also
- FireWire
- CameraCameraA camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
- Video cameraVideo cameraA video camera is a camera used for electronic motion picture acquisition, initially developed by the television industry but now common in other applications as well. The earliest video cameras were those of John Logie Baird, based on the electromechanical Nipkow disk and used by the BBC in...
- Digital VideoDigital videoDigital video is a type of digital recording system that works by using a digital rather than an analog video signal.The terms camera, video camera, and camcorder are used interchangeably in this article.- History :...
- OpticsOpticsOptics is the branch of physics which involves the behavior and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behavior of visible, ultraviolet, and infrared light...
- LensPhotographic lensA camera lens is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.While in principle a simple convex lens will suffice, in...
- MicroscopeMicroscopeA microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
- TelescopeTelescopeA telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
- Endoscope
- Lens mountLens mountA lens mount is an interface — mechanical and often also electrical — between a photographic camera body and a lens. It is confined to cameras where the body allows interchangeable lenses, most usually the single lens reflex type or any movie camera of 16 mm or higher gauge...
External links
- 1394 Trade Association
- Complete list of Firewire cameras
- Supplier overview
- Full line of Firewire IEEE1394a and IEEE1394b cameras and peripherals
- Imaging Solutions Group FireWire Cameras
- FireWire video cameras - for industrial, scientific and medical applications
- Photo cameras
- Video cameras
- Special cameras
- Operating System APIs
- Operating System APIs under Linux
- Application software under Linux