Black Box Dual 2.7 and iPATH 2.3, ServSwitch Dual 2.7 and iPATH 2.3 Chapter 1: Magic Eye and Dithering

Chapter 1: Magic Eye and Dithering

Dithering is a technique used to improve perceived image quality by creating the illusion of more shades of color than a display

can actually produce. By diminishing harsh transitions between colors, dithering can remove the “banding” that appears in areas

of gradually changing color or brightness, such as photographs of the sky.

Dithering was quite useful a few years back when LCD panels were only capable of 6 bits of color per pixel. The DV I specification

for the graphics cards used a maximum of 8 bits, and the monitors simply ignored the bottom bits of data. It was very easy to see

banding and harsh transitions.

However, technology moves on, and we all now use monitors with 8 -bit color so the need for dithering for LCD panels is simply

gone.

Dithering technology is still in play today, with it being available on Nvidia and ATI graphics cards. Apple® still uses the technique

on all its computer products.

Unfortunately dithering is an issue for us because, at a digital level, it appears that every pixel is changing color all the time, even

when the image is static. This requires up to five times more network data than can be carried by Gigabit Ethernet. The result is a

reduction in video frame rate, which the user sees as slow mouse response and jerky video content.

The Magic Eye feature reduces network traffic by ignoring small variations in the video from frame to frame. When it is used with

Apple® Mac® computers and other host computers that have dithered video output, Magic Eye enables the ServSwitch Agility to

transmit high frame rates, providing instant mouse response and smooth video playback. It can also be used to improve

performance if the video source is noisy ( e.g. from a VGA-to-DVI converter).

Magic Eye is enabled by default as it is not obvious to the user that poor mouse behavior is caused by dithering. In most cases,

Magic Eye is invisible, but it can, of course, give slight color inaccuracies on the monitor. For full color accuracy, Magic Eye can be

disabled for video sources that are not dithered or noisy.

For applications where color accuracy is vital, we highly recommend disabling video dithering altogether.

The only way to tell is to look at the network traffic generated by the ServSwitch Agility unit.

On average, a single 1920 x 1080 screen with a background refresh rate of 32 frames will use about 5–6% of bandwidth.

A dithered source will generate about 700 Mbps of data, or 70% of available bandwidth.