All you need to know about frame grabbers!
Epiphan VGA2USB and DVI2USB Frame Grabbers
Frame Grabbers: What are they?
According to Wikipedia, a frame grabber is “an electronic device that captures individual, digital still frames from an analog video signal or a digital video stream.” In other words, it is a device that takes an analog video signal or a digital video stream and converts it into a digital format that can be used for recording, archiving, post-processing, and even broadcasting! Two types of frame grabbers exist: analog and digital. Analog frame grabbers, according to Wikipedia, are used for the capture of NTSC/SECAM/PAL signals (regular television signals). If you are looking for a simple frame grabber like that, it can be easily bought in any large electronics store. Pinnacle seems to be a popular choice amongst those who would like an external solution, whereas more recent internal video cards from companies like Nvidia and ATI already have that function built-in.
The Good Stuff: Digital Frame Grabbers
This review will focus on digital frame grabbers, also referred to as with names like “framegrabbers” or “VGA grabbers”. Digital frame grabbers come in all sorts of forms and flavors. Many are used for the capture of Camera Link and GigE Vision industrial cameras, but those of special interest are devices that capture from a generic VGA or DVI stream, like that of an ultrasound machine as well as of an ECG (electrocardiogram). There are many companies that make frame grabbers capable of capturing a VGA (or even DVI) stream. There are several companies which manufacture internal PCI-based VGA frame grabbers. These include PixelSmart, Foresight Imaging, Unigraf, EMS Imaging, and Ncast. Epiphan Systems also makes an external USB-based solution for the capture of VGA and DVI signals.
Problem at Hand
With the need for a frame grabber that would be able to monitor medical devices round the clock with minimal or no adjusting or maintenance, choosing the right device may be a difficult task. Also, due to the nature of what is being captured, the captured images and videos need to be of diagnostic quality (very high quality) and at a relatively high frame rate (over 30fps), with a resolution of at least 1280×1024, which is what is used by the GE LOGIQ Book XP ultrasound devices that these grabbers will be acquiring the VGA signal from. This leaves me with several alternatives: Epiphan Systems’ VGA2USB, Foresight Imaging’s I-RGB 200, Unigraf’s UFG-03, EMS Imaging’s XtremeRGB, and Ncast’s DCC 3.1. PixelSmart’s frame grabbers are capable of only low resolutions and marginal quality, meaning that their frame grabbers are not sufficient for most applications.
Initial Comparison
Before diving in and buying any of these devices, it is important to compare their specifications based on the manufacturer spec sheets to see which are viable alternatives for the chosen application. Below is a short summary.
|
Manufacturer |
Model |
Price |
Type |
Maximum update rate at 1280×1024 |
OS Compatibility |
| EMS Imaging | XtremeRGB | $1400 | PCI (Internal) | 40 fps | Windows |
| Epiphan Systems | VGA2USB LR | $799 | USB (External) | 51 fps | Windows, Mac OS X, Linux |
| Foresight Imaging | I-RGB 200 | $1000-$1500 | PCI (Internal) | Not specified | Windows |
| Ncast | DCC 3.1 | $1995 | PCI (Internal) | 50 fps | Windows, Linux |
| Unigraf | UFG-03 | $2500 | PCI (Internal) | Not specified | Windows, Linux |
Pricing is especially important if you have a tight budget to work with. Based on this, the Ncast DCC 3.1 and Unigraf UFG-03 are immediately out of consideration. Their MSRPs (manufacturer suggested retail prices) are extremely overpriced for the offering. Epiphan Systems’ VGA2USB, an external VGA to USB frame grabber, sticks out of the bunch at just under $800, which is significantly lower than that of the other competitors.
When looking at the specifications, Epiphan Systems’ VGA2USB LR external frame grabber is the only one with support for Mac OS X and is also the one that offers the highest update rate. Remember that, even though the maximum update rates are 40-51 fps, the actual update rate will depend on how much of the captured image is changed from frame to frame. In other words, if your picture does not have much movement, you will be able to achieve maximum fps. Otherwise, expect lower numbers than the ones listed in the table above.
Internal vs. External
Epiphan VGA2USB Frame Grabbers and VGA Capture Devices
Are external frame grabbers superior to internal ones, or vice versa? In theory, internal cards would be better as they have access to a faster bus (PCI vs USB). In practice, however, due to the fact that both internal and external boards use on-board compression and buffers, the speed of the bus becomes irrelevant as both USB 2.0 and PCI are sufficient for high quality image transfer of up to 330 megapixels a second.
One must also consider the practicality of both alternatives. Each carries its own advantages and disadvantages. Below is a simple table for quick comparison.
| Advantages | Disadvantages | |
| Internal (PCI) |
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| External (USB) |
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Looking at the table above, the external (USB) frame grabbers seem to be the better alternative. What’s more, you do not need to disassemble your computer to install the grabber and it works with laptop computers, which is a very big advantage. This allows the user to use the VGA2USB for quick diagonstics of devices and effortlessly transport the frame grabber for use with other devices as well.
The Verdict
Internal frame grabbers, like the one from EMS Imaging, are an excellent choice for those that are planning to use a desktop PC with an available PCI slot without moving it around too much. For the most people, however, external capture devices are simply more practical.
What’s more, Epiphan Systems’ VGA2USB series of devices are just a fraction of the price of comparative PCI cards, with the base VGA2USB model starting at $299.
The VGA2USB LR can be used in rackmount as well as environments with small space restrictions. The device is only about the size of a credit card (it terms of length x width) and is very lightweight, which makes it very practical in setups where one does not have a sea of space to work with.
After testing the device, the picture quality turned out to be as promised – lossless and diagnostic, and the frame rate is constantly above the 30 fps mark. Epiphan Systems’ VGA2USB LR seems to be the perfect fit for anyone looking for a high quality, reliable yet relatively low priced VGA capture solution.
Here is a great resource to compare specs of different frame grabbers in a single table.
