Common topic - Whats a video scaler to a line doubler? (1 Viewer)

[Matthew Will]

Ok here should be an easy question for you guys. I understand how a line doubler works by increasing the frequency of the scan rate to effectively produce a sharper, smoother image. But what is a video scaler? I hear it is a device that allows a projector to project its maximum resolution. How does it do this? When would a video scaler be used instead of a line doubler? Are a line doubler and video scaler allowed to be used simultanously to produce an extremely sharp picture? I assume people use the PC's to bring out the maximum resolution for projectors like a video scaler does but how? Let me know. Thanks. Matt

 

[ManW_TheUncool]

Hmmm... That's an odd way of describing what a linedoubler is. It does what you say--well, not necessarily the sharp part--but that's not exactly "how" it does it.
Essentially, a linedoubler just doubles the # of scan lines (or apparent vertical resolution) of your interlaced source signal to create a progressive signal. That should usually mean doubling the scan rate. How it's actually done can be quite different from design to design although reversed 3:2 pulldown is the most important (and common nowadays) way of doing it since it can theoretically yield perfect reconstruction of the original frames of film-sourced video. Most any other method will involve some sort of interpolation/extrapolation that creates the extra resolution that did not really exist in the source video, and such methods would be necessary for video-sourced signals.
Scalers can be used to scale the resolution of the source video. Depending on the application, one might use a scaler to scale vertical resolution, horizontal resolution or both. Scaling could mean reducing(!) resolution as well as increasing.
Some commonly used applications are:
1. Scaling to match the fixed-pixel resolution of a display like plasma, LCD or DLP whether it's front projection or rear projection or "direct-view".
2. Scaling to an optimal TV scan rate for optimal convergence like is done on the Hitachi and Toshiba TVs (and JVC also) at their 540p/1080i output.
3. Scaling to a common resolution like 1080i for ease-of-use or to avoid issues like 480p being locked into FULL mode like can be done in a set-top-box. For example, my current HD cable box scales everything to 1080i on its component output. The Samsung SIR-T165 OTA HD receiver can act as a hub that upconverts all its video inputs to 1080i also. Some DVD players can scale non-16x9 DVDs to 16x9 480p image for proper display on TVs that lock into FULL mode.
As you can see, scaling can be done on an external dedicated scaler or as a function of a display device or a video source component. The same can be said of linedoublers. The more important thing is actually the quality of the scaler (or linedoubler). For example, people use external scalers (or HTPCs) for their fixed-pixel front projectors because the built-in internal scalers are usually not that good. Same can be said about linedoublers although maybe less so nowadays.
Technically and theoretically, linedoublers and scalers do NOT make anything sharper. At best, they will come extremely close to remaining faithful to the source video while making it look better and/or bigger to us. More likely than not, the video will actually look duller or softer or grainier, not sharper, which people often consider to be more film-like. So that's not necessarily a bad thing. However, in nearly all practical cases, scaling adds artifacts to some degree, whether they are readily noticeable or not.
Finally, a scaler can also be a linedoubler, OR more accurately put, the same device can have functionality for scaling and linedoubling. And technically, this could just be a single-chip device. The single Mediamatics chip used in various DVD players like the JVCs can even do DVD decoding + linedoubling + scaling all-in-one.
_Man_