Home' RTCA Documents for Review : DO-230H FRAC Contents 187
©2017 RTCA, Inc.
Pixel shape affects resolution or perceived sharpness. A screen’s physical aspect ratio and the individual
pixels’ aspect ratio may not necessarily be the same. An array of 1280×720 on a 16:9 display has square
pixels, but an array of 1024×768 on a 16:9 display has rectangular pixels.
The RGB color standards govern how red, green, and blue components of light are added together in various
ways to reproduce a broad array of colors. The standards derive from studies of how humans perceive color
and apply to sensing, representation, and the display of images in televisions and computers, and to a lesser
extent also to photography.
An RGB component signal consists of three monochrome video signals, each representing the image for
one of the primary colors; combining these three monochrome images in a display results in a full color
image. Possible sources of RGB video include cameras, composite decoders, character generators, graphics
systems, color correctors, and displays. Most computer monitors display color imagery using RGB
RGB signal formats are often based on modified versions of the RS-170 and RS-343 standards for
monochrome video. RGB signals generally use the same peak-to-peak amplitude as the luminance signal
in the local composite standard. This explains why there are several RGB standards and why it’s important
to determine the characteristics of video equipment and calibrate for the appropriate levels.
Recording and Storage
Video storage is a major element of video system design, and often the most costly element.
There are several options available for the user, including:
Direct Attached Storage (DAS), where the storage device is attached directly to a workstation or
local server. DAS is only suitable for small systems or systems where sharing video over a network
is not planned. PCs with internal and/or external storage drives are common examples of DAS.
DAS devices are not network appliances but the data they contain can still be shared among
multiple computers which have shared ports. Redundancy and fault tolerance depend on the hosting
Networked Attached Storage (NAS), which as the name implies are designed for sharing video
across a network. NAS devices are network appliances which act as file servers and contain file
sharing software, and may contain multiple disk drives including RAID drives (see below).
Network video recorders (NARs) are examples.
Storage Area Networks (SANs) network appliances that provide dedicated storage for enterprise-
level networks which are able to span multiple storage arrays including arrays at different locations.
Within these categories there are several means of configuring and interfacing storage drives. Any of the
following may be found supporting a video surveillance system depending on the system architecture and
Serial AT Attachment (SATA), the predominant way of attaching storage devices to a workstation
Small Computer System Interface (SCSI), for transferring data between computers and other
devices, and known as iSCSI when data are to be transferred across a network,
Serial Attached SCSI (SAS), which uses a serial point-to-point protocol to deliver bi-directional
file transfers. SAS drives have greater bandwidth than SATA drives, run bi-directionally, and are
designed for higher reliability. The network architecture should be designed for the higher
performance of SAS, keeping in mind that video transfers are done in real time, not in a store-and-
Links Archive Navigation Previous Page Next Page