Introduction

For the last 3 months, I've been evaluating the Epiphan VGA2USB, an external VGA capture device. Using the VGA2USB, we've been able to provide you with true high-definition captures of the latest Xbox 360 games, as well as compare video quality among different graphics manufacturers. Let's take a closer look at what the VGA2USB can actually do.

So what is the VGA2USB?

The VGA2USB does exactly what you would expect it to do based upon its name. It's a device that takes an analog VGA signal and converts it to a digital image over the USB 2.0 bus. This allows you to capture any image from any VGA device. What's even cooler is that the VGA2USB is fully bus-powered and it's only about the size of a deck of playing cards. It is essentially a mobile VGA capture device that captures at 16-bit color.

Epiphan VGA2USB (HD15 on on side)

Mini-USB connector on the other

Performance

If you've taken a look at any of our recent Xbox 360 articles, you'll see that we feature high-resolution screenshots rather than the lower-quality S-Video grabs that other websites feature, or relying on "developer units" that grab data directly from the frame buffer. This was all done with the Epiphan VGA2USB using the VGA cable from Monster Cable.

One of the limitations of the VGA2USB is that it has a limited sample rate. That is, while the device can capture 640 x 480 at 28 frames per second, it can only capture 1024 x 768 resolution images at 10 frames per second. Want 3 megapixel captures? 2 frames per second.

For many of the intended uses of the VGA2USB such as recording the output from scientific test equipment, the slow frame rate isn't a problem. Unfortunately, for games the story is different. When you exceed the optimal frame rate, you do not get a slideshow of "perfect" images. Instead, the fast moving portions of the screen develop striped interlaced artifacts where portions of the screen are from one point in time and other portions are from another point in time. This isn't a fault of the USB interface – PCI VGA frame grabbers have the same problem.

Lots of motion artifacts

Resolution	Frame Rate
640x480	28
800x600	20.6
1024x768	10
1280x1024	5.6
1600x1200	4.3
1920x1200	3.1
2048x1536	2.0

Where the VGA2USB really shines is in the quality of captured output. Before looking at the screenshots, you have to keep in mind that the VGA source signal itself is imperfect. (This is why we recommend DVI for LCD flat panels.)