MaximumPC 2005 11

XXXXXXX 2005 MA XIMUMPC 00

VIDEO QUALITY BENCHMARKS

Games are one of the best measures of a videocard’s

rendering horsepower, but Maximum PC readers don’t

buy state-of-the-art hardware just to play games. We con-

ducted these tests to measure each videocard’s ability to

process MPEG-2 video from a DVD.

The results surprised us. We had long suspected that

ATI did a better job of processing video, but these bench-

marks indicate the opposite. We also discovered that

DVD movies look terrible played back on nVidia cards in

SLI mode. nVidia tells us an SLI version of its PureVideo

decoder is in the works; until that’s released, SLI users

should disable SLI while watching DVDs.

DVD video is displayed at either 30 frames per second on a stan-

dard-definition TV (with each frame consisting of two interlaced

fields), or 60 frames per second on a progressive-scan high-

definition TV or computer monitor. Motion-picture film, however,

is shot, edited, and screened at 24fps, progressive scan. A

conversion process must be used to find a common mathemati-

cal relationship between film and video.

One of the most common conversion techniques is known as

3:2 pulldown, so named because one frame of film is repeated in

every fifth field of video. The videocard should detect the extra

frame and remove it, to present smooth motion. During electron-

ic editing, however, discontinuities in the 3:2 cadence are often

introduced. If the videocard doesn’t correct for this, the image

will lose detail.

Each of the nVidia-based cards passed this test without

a problem. The moiré pattern in the grandstands of the ATI

screengrab, however, reveals that the X850 XT Platinum Edition

lost track of the 3:2 cadence. We encountered this same prob-

lem with each of the ATI-based cards we tested.

Standard-definition video is interlaced, meaning each frame

consists of two fields; one containing the odd-numbered scan

lines and the other containing the even-numbered scan lines.

A standard-definition television draws the odd-numbered scan

lines first (1, 3, 5...), and then goes back and draws the even-

numbered scan lines (2, 4, 6...). This occurs fast enough that the

eye perceives the two fields as a single image, but interlaced

video creates images with scan-line artifacts in the form of jag-

ged edges along diagonal lines.

A videocard de-interlaces video, so each scan line is drawn

in sequence (1, 2, 3, 4, 5, 6...) on a progressive-scan monitor.

But this conversion process won’t remove scan-line artifacts

without additional processing. Motion-adaptive algorithms must

be applied in order to remove the jaggies. Examining the stripes

in the flags in the two shots above, we can see that nVidia’s

motion-adaptive de-interlacing (the flag on the left) is fairly ef-

fective; while ATI’s (the flag on the right) is not.

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3:2 PULLDOWN

nVidia

MOTION-ADAPTIVE DE-INTERLACING

ATI

nVidia ATI