MP3 and PVP picture quality: videos and TV-out
All videos are digitally compressed, and the resulting picture quality depends critically on how well this was done when the material was recorded. Professionally produced material is generally of very high quality, but if you are processing your own videos, the "Improving player picture quality
" sidebar explains the steps you can take to minimize compression artifacts.
Within the player, video images are generated by a layer of software that decodes a stored video data stream. After this processing, it is handled in the same way as photos and other player images, so it behaves exactly as in the measurements above.
But there is one important difference: all videos operate within a reduced grayscale range. How the manufacturers recalibrate the videos into the player's overall grayscale has an important affect on performance. Four of the six players take shortcuts and don't properly set their grayscales. As a result, their videos deliver only about 80 percent of the Table 2 peak brightness and contrast-ratio values. One benefit is their videos don't suffer from bright compression. The Apple iPod is the only player that does it correctly. The Samsung YP-D1 tries to do the right thing, but it incorrectly sets the black level, so the video contrast ratio falls to only 104--compare that to the Table 2 values. Also, Samsung's proprietary SVI format introduces significant compression artifacts, but they are less offensive on its tiny screen.
The Archos AV500 and the Cowon A2 have a screen large enough for three (very friendly) people to view at the same time, but the TV-out capability makes the players useful for presentations to much larger audiences. Except for the Samsung YP-D1, all the tested players can output their images to a standard-definition TV. The TV-out images have a native resolution of 640x480, which is significantly higher than the player's own screen (except for the Creative Zen Vision, which also has 640x480). The higher resolution is a two-edged sword: images that look OK on the player's small screen may not look as good on a larger screen at higher resolution, and vice versa. Also, if there are images with text, graphics, or fine detail, such as in a business presentation, artifacts can have a major impact on picture quality. See "Improving player picture quality" for more information on these topics.
We evaluated the TV-out quality by looking at test patterns, photos, and videos on a calibrated professional television studio monitor. All of the players produced very good TV picture quality, although we had to adjust some of the TV monitor's controls to get the best picture. For the Apple iPod, the TV's color saturation had to be turned way up, and for both Creative players, it had to be turned far down. For the Archos and Cowon players, the black level had to be turned up significantly. After that, picture quality was quite good for all players. Note that lower-performance TVs may not be able to produce as good a picture as the player's own screen.