Understanding your Home Theater Projector Resolution

In general, resolution of a screen refers to the number of lines of picture image displayed on screen. The more number of lines, the better the picture quality. An important understanding that any home theater projector user must have is the difference between a signal resolution and the resolution of the projector. 

Signal Resolution  

First let's understand what signal resolution means. For example, a standard TV signal displayed on a standard TV set consists of 480 lines of resolution, abbreviated as 480p (progressive) or 480i (interlaced). HDTV (high-definition) signals contain more than 700 lines, available from 720p, 1080p or 10080i and hence their superior picture quality.  

What is the different between interlaced video signals and progressive scan signals? Interlaced video signal sends information to your machine in 2 consecutive waves, 1/60 seconds apart. For a 480i signal, that means your machine draws 240 even lines on the first wave and another 240 lines on the second. A progressive scan signal means all the lines are displayed all at once in sequence. A progressive scan signal produces a better image quality since there is less lag between the projection of 1 image to the next.  

The interlaced signals was originally used in the early days of CRT tv. CRT machines then could only receive up to 240 lines of signal at a time; therefore broadcast stations had to send its signals in 2 waves to form the 480 line image on tv.  

So then, does a 1080i signal produce a better quality image then a 720p? 1080 lines versus 720 lines, 1080 is better right? That may be true, but not for all cases. The catch is, interlaced signals contain a lag, the actual projection of images is 540 at a time, lower then the 720 of progressive signals. When watch high motion videos or wildlife documentaries, this different in quality becomes significant.  

Projector Resolution  

LCD and DLP projectors both come in various resolutions, but the resolution inherent to the machine is "fixed". Other then the CRT, LCD and DLP projectors are designed with fixed number of projection pixels. The projector's fixed resolution may not be exactly the same as the resolution of the incoming signal. Therefore, the projector must first resize the signal image internally to match it with its own fixed-resolution panel.  

In computer resolution terms, 480 lines is equivalent to 640 x 480, 1280 x 720 for 720 lines. In general, the adage of rubbish in-rubbish out holds. If you input a low resolution (for example 480p) video signal into your projector, the upscaling (to 720p) will be performed by mathematical interpolation to fill in the addition pixels in-between. This is where the upscaling lag in projectors comes from. Understandably, the 720p wont be HD despite its HD resolution. That is with the exception of CRT projectors which do not have fixed resolutions; however, CRTs are rarely calibrated to project HD signals.

As a general guideline, always try to adjust the video signal to fit your projectors native resolution for best viewing quality. 

Fixed-Resolution Projector Panels 

• SVGA = 800 x 600 pixels (S for Super, non-HD)
• XGA = 1024 x 768 pixels (X for Extended)
• WXGA = 1280 x 720 (W for Widescreen)
• SXGA = 1280 x 1024 pixels (uncommon)

*VGA stands for Video Graphics Array 

These terms represent the fixed resolutions of a projector's internal panel. Any incoming signal must first be scaled to these fixed resolutions before it can then be projected.

If youre thinking of saving some money by buying the cheap SVGA, think again. 800 x 600 is still way better than your common CRT tv right? Now consider this. If you feed in high quality signals of 720p wide-screen image to a low resolution (SVGA 800 x 600) projector panel, it will be shrunk by 38% so that the original 1280-pixel-wide signal image will fit onto the 800-pixel-wide SVGA panel. A proportional shrinkage in the vertical dimension means that, the image will contain only 450 lines, which is even lower than the standard 480 lines! If youre really looking out for quality, top up some cash and get that XGA!