2. The Most Important Piece

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The make-or-break features, as I learned the hard way while working as a DVD section editor for a national magazine, are the video processor and especially the MPEG decoder. The video processor has to take the interlaced image and turn it into a progressive scan image. It also does the scaling. The decoder, on the other hand, decodes, decrypts and processes the image.

The problem all blew up in my face when I reviewed "The Incredibles." The film is full of bright red, which is the color most prone to problems in digital playback. The reason is this: video information is sent down as luminance (black and white), blue and red channels. These are the Y, Cb and Cr channels, respectively, but listed as Y, Pb and Pr on your component video cables.

Luminance contains all the detail of an image. While dogs can only see in black and white, we're not that much better than our four-legged friends. Human eyes recognize black and white much more readily and easily than they recognize colors, which is why black and white contains all the details. So four samples of black and white are sent down in a signal burst, followed by two samples of blue and one of red, because human eyes are not as sensitive to red as other colors. Both MPEG-2 (DVD's codec) and MPEG-4 (likely used in HD-DVD and Blu-Ray) use 4:2:0 formatting.

Because red is undersampled in MPEG-2, DVD players compensate by upsampling the video to at least 4:2:2, although now they are upsampled to 4:4:4, to push the same amount of red light as blue light. However, that means making chroma information that isn't there. In other words, the DVD player makes an educated guess, and you know what happens when you guess. So reds are most likely to suffer from problems on DVD players because of this.

Poor upsampling of the reds is what's known as a Chroma Upsampling Error, or CUE. People often refer to this as "the chroma bug" in DVD players. The "chroma bug" manifests as jagged lines around curves and diagonal lines, like you see in a video game when anti-aliasing is turned off in the video card settings.

This problem has existed since DVD players were first introduced, but few ever noticed since so many of us were watching DVDs on 27" and 32" CRT TVs. Then widescreen TVs suddenly became more affordable, and people were trading their 27" TVs for 50" and 60" sets. With the image blown up, problems became much more apparent. You would be amazed at the number of DVDs that look stellar on a 32" tube but look like a bad AVI file on a 60" plasma display.

The chroma upsampling bug (above) and how it looks when properly displayed (below) (Source: Secrets of Home Theater High Fi).

• DVDS-2500 DVD Player...
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  • $199.95
• • Advanced Lamps
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