Video Projection, or How I Learned to Love RGBHV

by Chris Eschweiler

After listening to Robert Pritchett’s recent appearance on the Mac ReviewCast (Episode #121 - ) with Tim Verpoorten, I thought I'd put my two cents worth in on the topic of S-Video vs. VGA connections to feed signal video projectors.

Between portable computers with blazingly fast processors and video cards capable of tremendous feats of visual acrobatics, presenting before a group of people has officially become technically trivial. You can walk into a conference room, connect a cable between your Mac and a projector and within seconds you can be showing a presentation filled with pictures, videos, charts, text and even (gasp) clip art.

In MacReviewCast #121, Robert asked this question:  with so many connection options dotting the back of modern video projectors, what’s the best path to use? Specifically, what’s the best input option: S-Video or VGA?  Let’s compare the two.

First Comparison: The Numbers

I know, I know: many folks hate math. But this is nowhere near as confusing as a tax return, I promise. As a (very) general rule, most smaller video projectors have a native resolution of 1024x768.

Newer projectors are going even higher and displaying 16x9 format images as well. These resolutions are found as output options on Macs and PCs. Output can be set as low as 800 x 600 or all the way up to 1920 x 1080 depending on the video card in your computer.  

On the other hand, the visible resolution of S-Video is 640 x 480 or about 30% smaller than our common-law standard. That means that if you were to switch from VGA signal to an S-Video signal, you'd have 30% less information to make the same eight foot wide picture on the wall in the conference room.

When it comes to displaying pixels, there is no such thing as good conservation.  It really comes down to how much you are willing to lose. If your presentation is important enough for you to endure sweaty palms and butterflies in your stomach, why should you toss out thirty percent of your presentation before you even introduce yourself?

Second Comparison: Conversion

Since computers display a high resolution natively, a VGA connection will simply pass that signal along to a projector which is designed to handle that information directly.  Using S-Video, you first have to downcovert the signal to S-Video as it comes out of your laptop, transmitting your signal through the s-video cable to the projector. Then the projector has to upconvert the signal so that its circuitry can paint the image on the previously-mentioned 1024x768 LCD image panel.  There's no benefit to converting the signal twice, and every time you do you lose detail.

Third Comparison: Compatibility

As you make presentations to more and more people, and to larger and larger groups, you may need to interface with larger projectors. Most mid-sized projectors take VGA input, but some larger projectors only take an input with five BNC connectors (one wire each for Red, Green, Blue, Horizontal Sync and Vertical Sync). 

For the highest fidelity, you want to use the high res output from your laptop without downconverting. All you would need is a VGA to BNC breakout cable. For $11 or so, you can interface over high quality RGBHV BNC cable to any high-end projector or even a video switcher.

Some projectors can be configured to use those five BNCs to ingest several different flavors of video input. Got a composite signal to project? Just plug your composite signal into the Green input BNC (which may also be labeled "Y") on the projector and find the menu item that tells the projector that’s the flavor of video you'll be supplying.  Viola! It’s like your old VCR. Easy...but not nearly enough video information to paint a really large screen.

Say you have S-Video. If the projector supports it, you can send it an S-video signal to two of the BNCs. You would need another adaptor, though. Here's one example.

Typically you plug it into the channels marked Y and C on the projector.

So to wrap up, you want to use the highest resolution signal path possible. There's no benefit to downcoverting your content just so you can use an old RCA cable from your Atari 2600. Sure, composite video is what everyone is familiar with in a home setting, but in the world of live events, nobody uses less than a hi-res signal at 1024 x 768.

Say you have S-Video. If the projector supports it, you can send it S-video to the BNCs...you would need another adaptor, though.  (Here's one example.)

VGA-DVI adapters,

six RCA FEMALE TO BNC MALE ADAPTERs

and half dozen of

BNC FEMALE TO RCA MALE ADAPTERs. 

Yes, it's an expense, but they are cheap insurance to ensure you’re never just  $2.99 away from having a successful presentation.