Scaler

[Richard]

Other terms: Scaler, scaling, video processor, up-conversion, upconversion, line doubler

[i]Updated 05/19/2007[/i]

Starting 2009 our old NTSC broadcast system is going to be replaced across the nation with DTV, better known as HDTV.

In the past we had only NTSC video which uses 480i and comes in a variety of different connections and level of performance. Our displays have been 480i also and this is called the native scan rate. HDTV though is 720p or 1080i and that means your HDTV has one of these native scan rates and possibly one more, 480p. There were few displays that do more than two and with CRT dead and gone there is only one scan rate that will perfectly match the pixel matrix of our new digital displays. Connecting a 480i signal to a native 480i display is a straight forward process. Connecting that signal to an HDTV will not work until it has been converted to the native scan rate of the display. This process is called scaling and every HDTV has one that will convert most everything out there so you can view it on the display. We call this an internal scaler. Unfortunately many of the internal scalers of the past were quite poor significantly degrading the final image you see. While scaling has radically improved over the last 8 years even with current displays you may not get the last word on performance with out an external scaler. The way to get around that is to use an external scaler that does a far better job and set it to one of the native scan rates of your display.

The most common use of scaling is to turn interlaced NTSC video into a progressive scan rate to eliminate interlace artifacts. NTSC video is not nearly as straight forward as it may seem on the surface due to the fact that it is an interlaced 30 frame system and few sources are created that way unless captured directly with an NTSC video camera. Even then there are variations in how video cameras capture the image. None of this was critical with NTSC on NTSC displays but HDTV is a new system that is incompatible and even 10 years later the library of NTSC video content remains substantial. To view NTSC content on your HDTV the many versions of cadence for interlaced fields has to be properly detected so it can be deinterlaced into a 30 frame progressive image and that is the most critical element of any video processor. Once that is achieved the far simpler and straightforward function of scaling or converting to the higher resolution of HD displays takes place. DTV and the inclusion of interlaced 1080i to support analog CRT technology during the transition to DTV brings similar interlaced NTSC concerns and problems with our new progressive digital displays.

Video cadence can come in up to 8 different types and most scalers and disc players are not designed to cope with them but external scalers typically can handle them all. Fortunately one video cadence is quite common, the 3/2 pull down required of 24 frame film. What this refers to is the fact that every 24 frames of film creates a video frame where the two fields come from two different film frames and they do not match creating an interlace error. This is actually the easier form of deinterlacing as once the computer in the scaler gets a good count on the film frame rate and where this error occurs it becomes a simple mathematical function to maintain the process. The other type of interlaced video is derived from video cameras. Since this frame rate of 30 already matches video it is much more difficult to determine which fields belong with each other to create a seamless frame. This is called adaptive processing as the computer has to be on it