Introduction
This article will explore methods used to capture VGA and DVI signals from sources such as PCs, servers, medical devices and embedded machines.
Once the VGA signal is captured, one can broadcast it over the web, archive it for later viewing, or even edit the captured images/video. The main advantage of having a VGA capture solution over a “screencasting” or screen recording software is that no software must be installed on the source machine, and the captured signal is a 1:1 copy of the VGA or DVI output. Many solutions exist for the capture of VGA signals ranging from simple inexpensive solutions to high-quality diagnostic capture devices.
VGA is used in a variety of computerized equipment, including PCs, servers, projectors, radars, medical equipment, scientific equipment, ATMs, and more. This article will thoroughly examine and evaluate methods that can be used to capturing the video signal from all these devices.
Terminology
VGA – Video Graphics Array: Connector interface for transferring analog video signal. Also known as D-SUB and RGB.
DVI – Digital Video Interface: Connector interface for transferring digital video signal.
HDMI – High-Definition Multimedia Interface: Connector interface for transferring digital video signal, audio signal, and has support for copy protection.
Frame Grabber – Device used for capturing a video stream and transforming it into a format that is readable by a PC. Also referred to as framegrabber, VGA grabber, VGA capture card, VGA capture device, RGB capture card, and others.
Capture Card – Similar to frame grabber. Internal PCI device that allows for video capture.
Devices Used for VGA Capture
Depending on the price range, there are many ways that one can capture a VGA signal. We will review wide range of solutions from average quality home use consumer devices up to high quality external frame grabbers that are suitable for recording VGA signals for educational, legal, industrial, commercial and military use.
For a low-priced solution with marginal quality and frame rate, one can use a VGA-to-Video Converter. This device takes the VGA signal and converts it into a video signal (RCA, component, or S-Video) which you can view on your television. You may then use any video card, such as those from Nvidia or ATI with video-in to record the VGA signal (now converted into an analog video stream) onto your computer. Alternatively, you may use an external capture device such as those from Pinnacle. In fact, since you have a standard video signal, you may just use a standard VCR (video cassette recorder) or a DVD DVR (digital video recorder) to record the output. All of these solutions would yield marginal quality with fairly low resolution of 640×480, but at a price point close to $100.
While the low quality VGA-to-video capture solution is satisfactory for some, more expensive solutions exist for high quality, high frame rate, and high resolution capture. Prices range from $300 to $3000, depending on the manufacturer and desired quality. These devices are commonly referred to as frame grabbers, as they “grab” an analog VGA signal and convert it into a digital USB stream that can be interpreted by a computer.
There are two types of VGA and DVI frame grabbers in existence: external (over USB) and internal (over PCI). To date, Epiphan Systems is the only manufacturer of high quality compact external USB-based VGA frame grabbers.
EMS Imaging, Foresight Imaging, Unigraf, PixelSmart and Ncast all manufacture internal PCI-based solutions. These devices all grab the VGA signal and have the ability to save it as a series of pictures (JPEG, PNG, etc) or a video file (AVI, MPEG) on the target computer. Some devices even support third party applications such as Windows Media Encoder or QuickTime Broadcaster in order to let the user share and broadcast the acquired VGA stream over the web. Frame grabbers are generally capable of capturing really high resolutions (up to 2048×2048 ) with very sharp colors and at high capture rates (up to 60 frames per second), and are deisgned for high quality capture applications.
Which Frame Grabber to Use?
The choice of frame grabber depends highly on the capture requirements of the user. Internal PCI frame grabbers need to be fitted into a desktop and are therefore difficult to move across different computers. They all require specialized driver software to be installed using administrative accounts. While suitable for home and consumer needs they might not be the best choice for corporate, industrial and secure environments where access to internals of signal source is limited or not possible. External USB frame grabbers, on the other hand, are very portable, lightweight, easy to move across different devices. They consume little power and are easy to move around. Some external VGA capture devices, such as entry model of VGA2USB grabber from Epiphan Systems, does not even require power source at all.
Some applications in which external frame grabbers are the only solution include, but are not limited to, medical device capture, air radar and marine navigation equipment capture, scientific and military equipment capture, and the capture of annotated courtroom evidence.
Of course, if the quality of the capture does not matter and the user has tight price restrictions, the VGA-to-video solution described at the beginning of this article would be optimal. In all other cases, USB and PCI frame grabbers are preferred.
In general, external frame grabbers are usually preferred for high-quality capture to internal ones because they are easy to store and integrate into computer systems such as a rackmount servers easily due to their small size, ruggedness, and portability. What’s more, installing a frame grabber does not require modification of the source device, which makes the VGA capturing proccess 100% secure. For example, during the Torino 2006 Olympics, Epiphan Systems’ VGA2USB series of frame grabbers were used to capture output from GE LOGIQ Book XP ultrasound machines used to diagnose athletes and broadcast the captured signal to radiologists over the web.
Summary table of the different offerings:(Device, Maximum Resolution, Maximum Update Rate, Internal/External, OS Support)
EMS Imaging Xtreme RGB: 2048 x 1536, 40 fps, Internal, Windows
Epiphan Systems VGA2USB Pro: 2048 x 2048, 60 fps, External, Windows+Mac OS X+Linux
Foresight Imaging I-RGB 200: 1600 x 1200, Not specified, Internal, Windows
Unigraf UFG-03: 2048 x 1536, Not specified, Internal, Windows+Linux
PixelSmart Video Extreme: 768 x 512, 30 fps, Internal, Windows
Ncast DCC 3.1: 1920 x 1200, 60 fps, Internal, Windows+Linux
Overall, the Ncast DCC 3.1 has the best specifications compared out of the internal PCI frame grabbers on the market.
Epiphan Systems’ VGA2USB Pro has the best OS support and is the only VGA capture device that supports Mac OS X. Epiphan Systems’ solution also has the highest maximum supported resolution.
Conclusion
For those that rarely capture VGA signals and do not need a high quality lossless picture, the combination of a VGA-to-video adapter and a simple video capture device would be a sufficient and low priced solution for their needs.
However, those that would like to capture lossless and diagnostic-quality images and video from any VGA source, including secure computers, laptops, military radars, marine navigational equipment and medical devices, require an external VGA frame grabber. While Ncast’s DCC 3.1 device seems to be the best available internal PCI card device, Epiphan Systems’ external VGA2USB Pro surpasses all other VGA frame grabbers in terms of capabilities and is the best frame grabber on the market to date.
Jeff Walt,
Chief Technology Strategist for MTI Corporation / North America.
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