Scan Converter vs. Scaler

By Anthony D. Coppedge
Contributing Writer
May 08, 2017

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There are two versions of this reply - Basic and Advanced. I offer both so that no matter where you are on the 'Techie-O-Meter', you can get direction on this often misunderstood subject:

First, the comments and question raised by a reader of mine, Scott Steffan:

My only comment on scan converters is that you will always lose resolution quality in the conversion from computer-RGB to S-video or composite video. At least this is my experience and I have only spent 200.00 on a scan converter.

Are there very good scan converters that you would have to split hairs to see the resolution quality difference when it makes it to screen?
- Scott Steffan

BASIC ANSWER

There is always a loss when down-converting (Scan Converting) from computer to video. However, a $200 scan converter is going to degrade the image severely. So, yes, there are very good scan converters that are offer only a slight loss of quality from the original computer image.

The RGB (usually HD-15 pin serial connection) is based upon a computer resolution input. In other words, you hook up the output of the computer to a box (Distribution Amplifier - like a P2/DA2) so that one output continues to the computers' monitor and the other runs out to the projector.

The quality of this image is based upon the output resolution of the computer. It is not uncommon to have 640 x 480 or 800 x 600 or even 1024x768 as computer outputs. The higher these numbers, the better the resolution (nice and crisp, not blocky).

It is best to find out what the "native resolution" of the projector is (usually 800 x 600 or 1024 x 768), and send the exact same output resolution from the computer to the projector. This will yield the best looking-image for that projector.

The SCAN CONVERTER comes in when you want to run a video signal to the projector (not RGB HD-15 pin). Why do this?

Let's assume you have a VCR, a DVD player and a computer that all need to be projected. To make "seamless" (no glitches, no blue or black screens in between) transitions between the DVD, VCR and computer, we need to 'agree' on a standard type of signal.

Since Computer signals are completely different from video signals, we need to make the computer common (scan convert) bringing it down to video. Now we can use a video mixer (switcher) to dissolve, cut, wipe and key in video - because all three sources (in our example) are now video.

In the above scenario, we lost resolution coming down from computer to video. But what if resolution is paramount? Glad you asked...

ADVANCED ANSWER

In order to send the computer signal and video signals together (from our example above) we can take a high-resolution Scan Converter to down-convert the computer to video. The more expensive scan converters ($1,500 to $4,000)look significantly better than an inexpensive scan converter. That's because they actually process the information better and look for the best use of their algorithms to determine compression and anti-flicker methods.

The 800 x 600 computer resolution looks ABOUT the same as a good quality component video source (RGsB, RGBS or RGBHV). Component video from a high-quality source will actually look better in many instances than 640 x 480 computer images.

Is it important to note that mixers/switchers like the Panasonic MX20, MX50 and Focus Enhancements MXPro all accept S-video and composite video. The Focus Enhancements MXDVPro includes two “firewire” (digital compressed) inputs. However, for video to look really crisp, component analog (Y,U,V; Y, Pb, Pr; RGsB) or SDI (Serial Digital Interface) is the preferred video input type.

Using a higher-end scan converter (with component or SDI outputs) will interface wonderfully and provide a very nice image. The cost differences, however, are tremendous. For example, the Ross Synergy1 switcher is about (list) $20K. The main difference: you can look just like the major TV networks in terms of DVE’s, DSK’s and video processing.

The biggest difference between video and computer signals is in the Interlaced Video versus the Progressive Scan computer images. The video image is scanned in odd lines first, then even lines. The result is an interlaced image. The 'black lines' evident in video will no longer be in
existence in a progressive scan image, as all of the lines are scanned progressively, in sequence (1,2,3,4,5, etc.)

So if you're looking at running computer resolutions 1024 x 768 or 1280 x 1024 or higher, then you won't want to down convert computer resolution (Scan Convert). Instead, you want to up-convert the video to match the computers' resolution (Scaler).

The higher quality Scalers ($2,000 - $6,000) will take video and up-convert very nicely to progressive scan images. In fact, you can now buy Scalers that have seamless switchers built right in that allow for cuts and cross-fades (dissolves) between computer and video sources...with all of the output at a fixed resolution to match the projector.

Scaling is in fact the best QUALITY image...but you won't be able to do DVE's or DSK's like you can in a video switcher.

SUMMARY

In summary: you can use Scalers if you want the ultimate in quality pictures and don't need lots of mixing options. If you want to have that “TV look”, however, you can use Scan Converters to down convert computers to match video.

Don't forget, the weakest link will kill the picture, so the highest level of video signal across the entire signal chain will yield better images no matter which methodology you choose. Again, remember, a $.99 cheapo connector just made that system worth $.99, so ensure that all of the pieces of the system are of sufficient quality.









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