FireWire camera
FireWire cameras use the IEEE 1394 standard bus for transmitting audio, video and control data. FireWire is Apple's brand name for the IEEE 1394.
FireWire cameras are available in the form of still cameras and video cameras that provide video and audio data. A special form of video cameras is used in areas such as industry, medicine, astronomy, microscopy and science. These special cameras no audio data.
Construction
The basic structure of FireWire cameras based on the following six modules:
Optics
FireWire cameras are based on CCD or CMOS chips. Their light-sensitive surface, as well as the individual pixels are small. For cameras with integrated optics, one can assume that the optics is tuned to these chips.
Interchangeable lenses are often used, especially in the field of professional and semi-professional photography as well as the area of specialty cameras. In these cases, a system specialist optics, chip and application must coordinate each other (see system integration). The interchangeable lenses is in addition to normal lenses also microscopes, endoscopes, telescopes, etc. With the exception of the standards C- mount and CS -mount interchangeable lenses of the connections are firm-specific.
Signal recording
Since the function of FireWire cameras based on electrical signals, the module converts " signal recording" the incident light and the incident sound into electrons. In the case of light this task is performed by a CCD or CMOS chip. The conversion of the sound is the task of a microphone.
Digitizing
The first step of digitizing the image is already clear by the construction of CCD and CMOS chips. They decompose the image in pixels. If a pixel collected many photons, it generates a high voltage, there were only a few photon, the voltage low. The voltage has analog values . Therefore, it converts the second step of digitization, an A / D converter into a digital value. This is the raw digital image is available.
The microphone converts sound into voltages. An A / D converter converts these analog values to digital.
Signal Conditioning
For the production of the colors in front of the CCD - or CMOS - chip a color filter. It is from pixel to pixel alternating red, green or blue. Therefore, the filter is called mosaic filter or after its inventor Bayer sensor. From this raw digital image, the module " signal processing " creates an image that meets aesthetic requirements. The same applies to the audio data.
Finally, the module compresses the image and audio data and presents it in video cameras as DV data stream. In the case of cameras, it provides the individual images and any existing voice comments as files.
The application fields of industry, medicine, astronomy, microscopy and science often use monochrome cameras without special microphone. You waive any signal processing, so give the raw digital image.
Certain variants of color cameras also give out only the raw digital image. They are called ColorRAW or Bayer camera. They are frequently used in industry, medicine, astronomy, microscopy and science used. As a still camera used by professional photographers. Semi-professional cameras often offer a RAW mode as an option.
The processing of raw digital images is outside the camera instead of on a computer and can therefore be adapted by the user to the task at hand.
Interface
The first three modules are components of any digital camera. The interface is the the FireWire camera module characterizes. It is based on the IEEE 1394 standard of the organization " Institute of Electrical and Electronics Engineers ". This standard describes a bus
It allows the simultaneous operation of up to 63 different devices (cameras, scanners, VCRs, hard drives, DVD burners, etc.).
Other standards describe the behavior of these devices. They are called protocol. FireWire cameras mostly use one of the following protocols:
Devices that use the same protocol can communicate directly with each other. A typical example is the connection of a video camera to a VCR. Unlike the USB bus so is a higher-level computer not necessary. If a computer is used, it must be compatible with the protocols of those devices be, with which it wants to communicate (see data exchange with computers ).
Control
The controller does the interaction of the individual modules from each other. The user can influence the control take over
Photo cameras
Professional and semi-professional cameras and especially digital camera backs often offer FireWire interfaces to transfer the image files and to control the camera.
For the transfer of image files, the SBP-2 protocol is used. In this mode, the camera behaves like an external hard drive, it allows for easy exchange of image files to a computer ( see data exchange with computers ).
To increase the working efficiency in the photo studio are cameras and camera backs can also be controlled via the FireWire bus. Normally, the camera manufacturers do not publish the protocols used in this mode. Therefore, the camera control requires a special software from the camera manufacturer, which is usually available for both Macintosh and Windows computers.
Video cameras
During the FireWire bus is distributed only in higher-quality cameras, you can find him in the field of video cameras already in amateur equipment. Video cameras are primarily based on the log AV / C. It also defines the flow of audio and video data as well as the control of the camera.
The majority of video cameras allows only the output of the audio and video data over the FireWire bus ( DVout ). Some video cameras also offer the recording of audio and video data ( DVout / DVin ). Video cameras exchange data with video recorders and / or computers.
Special cameras
In the fields of industry, medicine, astronomy, microscopy and science often come FireWire cameras are used which are not aesthetic, but for analytical purposes. Enter uncompressed image data without audio portion. These cameras are based on either the standard protocol DCAM ( IIDC ) or on company-specific protocols.
Due to their area of application, the special cameras differ in several ways different from photo and video cameras:
Special cameras themselves are therefore simpler structure compared to photographic or video cameras. An isolated use of these cameras, however, is meaningless. They are, like other sensors also, only components of a larger system (see System Integration)
Data exchange with computers
FireWire cameras can with any other FireWire device to exchange data, as long as both devices use the same protocol (see interface). Depending on the camera, these data
If the FireWire camera to communicate with a computer, it must have a FireWire interface and control the protocol of the camera. The early days of FireWire cameras was dominated by company-specific solutions. Some specialists offered to interface cards and drivers, to the access the application software directly. In this approach, the application software is responsible for the protocol. As this solution can take advantage of the computing resources very efficiently, you will encounter them in special industrial projects on even today. However, this procedure often leads that no other FireWire devices such as hard disks can be used. Open systems avoid this disadvantage.
Open systems are based on a layered model. The behavior of the individual layers ( interface cards, low-level drivers, high-level drivers and API) follows the requirements of the respective operating system vendor. Application software may only access the APIs of the operating system, but never on any layer below it. In the context of FireWire cameras of the high- level driver is responsible for the protocol. The low-level driver and the interface cards implement the guidelines of the IEEE 1394. The advantage of this strategy is the simple and independent of the hardware and their manufacturers to realize the application software.
In particular, in the areas of photo cameras and special cameras you will find mixed forms between open and company specific systems. Typically follow in these cases, the interface cards and the low-level driver to the standard, while the overlying layers are company- specific.
The essential characteristic of open systems is to not use the APIs of the hardware manufacturer, but those of the operating system. For Apple and Microsoft, the issue has image and sound a high priority. According to known are their APIs QuickTime and DirectX. They are lower, but to the playback of audio and video in the public perception. In fact, there are powerful APIs, which are also responsible for image acquisition.
In Linux, this API is called video4linux. Since it is less powerful than QuickTime and DirectX, have evolved in parallel with video4linux more APIs:
To simplify the use of the dedicated and video4linux APIs meta unicap API was developed. They concealed their details using a simple programming model.
System Integration
FireWire cameras are often only wheel of a larger system. An additional system specialist uses various other components to solve a specific task. There are two basic approaches:
Many aspects of system integration are independent of the use of a FireWire camera. This applies in particular to the high influence of the illumination on the result, be it an aesthetically or analytically oriented.
When creating application software, it is however a FireWire typical peculiarity, namely the availability of standardized protocols such as AV / C, DCAM IIDC and SBP- 2 (see also exchange data with computers ). These protocols taking advantage, you write the software independent of a specific camera from a specific manufacturer.
If you leave the implementation of the Protocol to the operating system and sets its Software on the APIs of this operating system, the hardware - independence is maximized. Uses such as Linux application software the API libdc1394 (see data exchange with computers ), it can access to all FireWire cameras that use the protocol DCAM ( IIDC ). The use of the API unicap allows additional access to other image sources, such as frame grabbers.