MP3 and PVP picture quality: the displays

Table 1 lists the most important display specifications for the six players in this roundup. There are three MP3 players with a photo/video capability: the tiny Samsung YP-D1 (with a 1.8-inch screen), as well as the fifth-generation Apple iPod and the Creative Zen Vision:M, both with 2.5-inch screens. We also have three larger PVPs (two with recording capability): the Creative Zen Vision with a 3.7-inch screen, and the Archos AV500 and Cowon A2, both with 4-inch wide-screen displays.

The size of the screen is almost always specified by its diagonal. The screens come in a variety of rectangular shapes, which are specified by the aspect ratio, the measure of the screen's width to its height. Standard-definition TVs and most digital cameras and computer monitors have an aspect ratio of 4:3 or 1.33. With 17- and 19-inch LCD computer monitors, the aspect ratio is a slightly narrower 5:4 or 1.25 (1,280x1,024). HDTVs have a considerably wider aspect ratio of 16:9 or 1.78. The tested players have the same range of aspect ratios. If the content you are showing has an aspect ratio different from that of the display, then some portion of the screen will go unused, so its effective size can be notably smaller than the listed value. All the displays are operated in landscape mode, where picture height is the smallest dimension, so it is a good indicator of how large the screen will seem.

Resolution is an easy specification to discuss: the higher, the better. But don't be turned off by the relatively low resolutions of these players--it's their pixel density, or dots per inch (dpi), that determines how pixelated the image appears. Again, the higher, the better, and these are relatively high in density. For reference, a 19-inch LCD monitor has an 86dpi.

The number of screen colors that a display can produce is frequently misinterpreted as an indication of its color gamut. It has nothing to do with the gamut but, rather, specifies the number of possible intensity levels for each of the red, green, and blue primary shades. Displays with 65,000 colors (16 bit) have 64 levels for green and 32 for red and blue. With 262,000 colors (18 bit), there are 64 levels for all three primaries, and with 16.7 million colors (24 bit), there are 256 levels. In principle, displays with more intensity levels will produce smoother images and less visible contouring, but there is very little visual difference between these players, which are driven by image files, player software, and hardware that automatically dither the intensity levels. The dithering is difficult to detect because of the very high DPIs.

It's unfortunate that most of the players have few if any adjustable user controls. The most important one is a backlight control that varies the brightness of the display. It is generally labeled Brightness, which is confusing because that term is also used for a control that adjusts the black level on TVs and many displays. Other convenient controls include contrast, color saturation, and black level. A black-level control allows the image contrast to be improved under bright ambient light, and it improves the picture quality on many videos.

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