MP3 and PVP picture quality: brightness, contrast, and viewing angles

Before we can analyze the picture quality of the players, we need to discuss the characteristics of their LCD screens--namely brightness, contrast, and viewing angles. The results shown in Table 2 were made with a laboratory Spectroradiometer and are discussed in the sidebar on technical information. The results are color coded: green means very good or significantly better than the other units; red means poor or significantly worse than the other units; and yellow means mediocre performance.

Brightness and contrast
Peak brightness is very important in bright ambient-light viewing conditions (the brighter, the better) but not for low ambient-light viewing. In fact, for low ambient light, it is generally best to reduce the peak brightness to improve viewing comfort. A backlight control is highly recommended for this, and as a bonus, it conserves battery power and lowers the black-level brightness. The Creative Zen Vision:M and the Archos AV500 are notably brighter, and the Creative Zen Vision is notably dimmer.

Black-level brightness is the residual dark glow that the screen and each pixel give off when they're supposed to be producing true black. It is distracting and washes out both the contrast and color saturation of the dark portions of the image (the lower, the better). It is very important in low ambient-light viewing conditions but not high ambient-light viewing because the player's actual viewing black level is dominated by the ambient light reflecting off the screen. The Apple iPod has by far the brightest black (not good), and the Samsung YP-D1 is the darkest.

The contrast ratio is generally considered one of the most important measures of display performance. It is calculated by dividing the peak brightness by the black-level brightness, and it tells you the range of brightness that the display can produce (the larger, the better). However, the contrast ratio is relevant for only low ambient-light viewing conditions because the actual viewing black level is affected by the ambient light reflecting off the screen. The Samsung YP-D1 and the Creative Zen Vision:M have the highest contrast ratios, while the Apple iPod and the Creative Zen Vision have the lowest.

Performance under bright ambient light
When these players are used in bright ambient light, the screen won't appear as dark because it reflects a certain percentage of the room light. This washes out the image by reducing contrast and color saturation. We measured the screen reflectance, which is the percentage of ambient light reflected by each player (the lower, the better). The Archos AV500 was the clear winner. The contrast rating is simply peak brightness divided by screen reflectance--again, the larger, the better. If you frequently watch a player under bright ambient light, then this may be the single most important specification. The Archos AV500 is again the clear winner, and the Creative Zen Vision:M is also significantly better than the other players.

Viewing angles
The brightness, contrast, and color saturation that you see on the screen varies with the viewing angle. If you're watching by yourself, the forward-tilt viewing angle will vary depending on how you hold the player. If you're watching in a group, people to the left and right of the screen will be positioned with a horizontal side viewing angle. The industry-standard viewing angle is not particularly useful here because it specifies the angle where the contrast ratio falls to 10, an incredibly low value that is meaningful for digital watches but not imaging displays. Table 2 lists the contrast ratio for a 10-degree forward tilt of the screen, which is the largest angle a single viewer is likely to use. Table 2 also lists the contrast ratio for horizontal side viewing at plus or minus 45 degrees, which is roughly what a person sitting next to the central viewer will see. These values provide a good measure of how the viewing experience varies with angle; again, the larger, the better. Note that the contrast ratio for the Cowon A2 increases significantly with a forward tilt. This is acceptable but not desirable. The Archos AV500 has the best performance because its picture varies the least with viewing angle. Note that all of these displays will produce a negative image (contrast reversal) if you view the screen at too large an angle.

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