Hurry up Digital Video Interface!

Did you know that the picture quality available from DVD is crippled? And it’s all thanks to the analogue connections. It doesn’t matter whether your DVD player puts out progressive scan or interlaced video, you are not getting all the horizontal resolution on the disc.

The video is held on a DVD at a resolution of 720 pixels across by 576 (PAL) or 480 (NTSC) pixels vertically. But the analogue connection standards — even if you use a component video connection — support only 500-ish pixels horizontally. This can’t be increased within the standard because the analogue signal will not carry more data. The scanning frequency is fixed. Progressive scan doubles the scanning frequency, but it uses this to double the number of lines sent, not double the amount of information on each line.

For some time a way around the crippling has been on the horizon. That’s the introduction of the DVI-D interface (Digital Visual Interface – Digital*). Already available on a number of high-end computer video cards and an increasing number of high end home theatre projectors and plasma displays, it has thus far appeared on just one DVD player: the Bravo D1. DVI-D promises an increase in horizontal resolution of up to 44% (compared to PAL’s clearly visible 20% boost in resolution over NTSC).

There are other advantages to a direct digital connection as well. It avoids the digital to analogue conversion in the DVD player, and the subsequent analogue to digital conversion in the display device. To quote from a review of the Bravo D1:

When using the native 480p output, the Bravo D1 delivered an image that was very subtly sharper than the Denon [DVD-3800]. But more importantly it was noticeably more stable with fewer artifacts and less jitter.

The problem has been that the DVD Forum is concerned that allowing full-resolution digital video output would facilitate DVD piracy. Yeah, sure. As though the pirates who sell DVDs with ‘This is a promotional copy’ banners dancing across the bottom of the screen, or movies captured with a video camera placed in a cinema, give a stuff about quality. Still, the Forum’s nerves have been somewhat settled by the development by Intel of the High-bandwidth Digital Content Protection (HDCP) encryption protocol. Basically, this will allow a DVI-D-equipped DVD player to handshake with a similarly equipped display device, establish an encryption key, and then feed it the signal at full resolution in uncompressed digital format.

Actually, there is one way of watching full resolution DVD at the moment: that’s using a computer-based DVD player. And this allows me to demonstrate the actual differences in the picture quality. I grabbed a frame from the Superbit version of The Fast and the Furious (chosen because of its very high video quality). The picture below shows at the top a detail from the original frame (captured at the original resolution of 720 by 576 and then Photoshopped to 1024 by 576 to show the correct aspect ratio), and at the bottom the same detail, first Photoshopped to 500 by 576 and then to 1024 by 576. The bottom one thus approximates the quality that you actually receive using an analogue connection.

The detail is part of the background from the car performance shop interior, just a 150 by 50 pixel slice, which I have doubled in size to make the differences clearer on screen (remember, if you use a projector the picture will look quite large).

Look first at the vertical slats to the right. Notice how clearly defined and evenly spaced they are in the top shot, and how fuzzy and uneven they are at the bottom.

Then look at the right hand blue tank. See how the highlight has fuzzed up and almost disappeared. Then look just to the right of the white pole. Near the top you’ll see two very fine dark vertical lines. At least, you’ll see them if you look at the full-resolution top shot.

Where you won’t see them is in the 70% resolution bottom shot.

* The ‘D’ on the end of DVI-D is to distinguish it from DVI-A. The standards designers have sensibly allowed the physical connections to be capable of handling analogue signals as well as digital, using different cables. Obviously, only a DVI-D connection will realise the higher resolution. The DVI-A capability is there just as a convenience.

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