Getting the Picture

I sat in on a product demonstration for a projector the other day. While the projector was impressive in terms of brightness, noise level, and ease of set up and operation, I was not impressed with the image. It seemed a bit fuzzy. The material on-screen was a rather generic slide show, and the projector had been set up and focused properly. Then I realized what the problem was. It wasn’t the content or the projector, but the fact that the projector and computer were at different screen resolutions. I mentioned this to the rep, who very quickly reset his laptop so that they were matched and the image was improved dramatically. It was a pixel for pixel match to what the computer was putting out.

Video scalers can be both a blessing and a curse — often at the same time. While a scaler will allow us to adjust the input resolution or even the format to match a specific output format, it does not guarantee our image quality. As a result, what may look beautiful on the local monitor may look bad projected on a display —the kind of bad that clients remember.

So what are these resolutions and how do we get a handle on them?

I have said before that I believe that projectors will plateau at a resolution of 1080 for a while because of the HD standard and because it will give the market a chance to catch up. But interest ingl y enough, projectors have only recently come out with resolutions of 1080 pixels. Most proj e c tor s topped out at SXGA+, giving them 1050 pixels. So what happens to those other 30 lines of information? They get lost in the scaling. They can either be thrown out and part of the image is cut off, or they get squeezed in and the image has this very slight fuzzy appearance where it occurs. On an SXGA+ screen trying to reproduce a 1080 image, the distortion is slight and often unnoticed except by a trained eye.

What about all those other resolutions out there? What are we supposed to do about them? Oversized images can be reduced to fit on screen although it is just reducing the image size by throwing out pixels until it fits. This is where scaling can be a blessing or a curse. How the scaler eliminates pixels to produce the final image determines the quality of the finished product. If it is done smoothly and evenly, the image will still look good when it is done. If it is done poorly, the image will either look cropped (if we’re lucky) or it will look like the vertical and/or horizontal clocks are out of phase. Has your computer monitor ever looked like part of the verticals on the lettering was missing, but when you reset the screen resolution it all came back properly? That’s what I am talking about.

The other place that scaling helps and hurts us is with screen format. If we use an SXGA (not plus) projector, we give up not only 26 pixels of vertical resolution, we also surrender 400 pixels of horizontal resolution. If we feed this projector a 1080 signal, it will get squashed big time before it hits the screen.

All of the major and most of the minor projector manufacturers have taken care to install good quality scalers onboard their projectors. Still, just like in audio world, there are a number of even better quality outboard scalers that do amazing jobs of helping us get our images under control. I hope to review a few of these in the coming months.

The other side of the scaling issue is taking smaller images and enlarging them to fill the screen. If you are doing a presentation and the source material is originally SVGA (800×600) or even XGA (1024×768), it will have to be scaled up to fill the screen.

As the image is stretched to fill the screen, the scaler has to extrapolate between two pixels or two lines and calculate how to fill the missing information. Our new image is going to blur a bit or look pixilated (sometimes called tiled or mosaic). There is no simple solution to this other than to recreate the source material in the proper resolution. An alternative way to get around the scaling issue is to convert the image to a standard (SVGA) or high def (XGA) video signal and then process and project it.

Next month we will look at these resolutions and what they mean on screen in terms of quality and size. In the meantime, enjoy what is left of summer.

Paul J. Duryee is the systems design lead at Maxx Technology. He recently got his hair cut. He can be reached/ridiculed at pduryee@plsn.com