Resolution is often the #1 consideration of HDTV buyers when selecting their sets. The question is, is resolution the most important? Many people are surprised to hear that resolution often is not the most important factor. Resolution is an easy statistic to put on a stat sheet, but other television abilities are often more important, though not as easy to document.
It is important that we establish what it is we are referring to when we discuss television resolution. Resolution is described by the number of horizontal pixels by the number of vertical pixels. When one number is used, it is always the smaller, being the number of pixels from the top to the bottom of the screen. Next is whether the television is "interlaced" or "progressive scan", noted by the letter "i" or "p" behind the vertical resolution number, often 480i, 480p, 720p, 1080i, and 1080p. The difference between interlaced and progressive is that an interlaced picture has all of the odd lines drawn on the screen in one pass, the even lines are followed in the next pass. A progressive scan image has all of the lines drawn onto the screen in a single pass, leaving the picture more clear, particularly for fast-action coverage such as sports. Since it takes two passes for an interlaced image, every 1/30th of a second the complete picture is drawn compared to progressive scan, which takes half as much or 1/60th of a second.
The first and most important point to this discussion is that typical HDTV is not transmitted in 1080p. Some networks send their data in 1080i, many send their signals in 720p. At this time, the only native 1080p content comes from Blu-Ray, some video games, and sometimes computer signals. Currently the satellite providers are marketing some video-on-demand as 1080p, but the bandwidth sent has caused their 1080p signal to get some criticism about their accuracy.
As discussed in previous the previous blog topic, The Digital Transition, the NTSC format set 480i as the resolution of color television from 1953 through 1989. Progressive scan was introduced with DVD, and DVD 480p proved that progressive scan is much better than interlaced for much content. The DVD players which could show progressive scan were required to be wired using a new analog connection technology, component video, compared to coaxial, composite, and S-video. When HDTV was first being sold, both 1080i and 720p televisions were manufactured. By comparison, these two resolutions were very similar. Broadcast television, as is still the case, is sent in 720p or 1080i. At some point, the advantage of progressive scan was realized so much that 1080i televisions stopped being produced and 1080p televisions began to dominate the market.
So with all of this better understood, doesn't it stand to reason that a 1080p television will be much better than a 720p television? Not necessarily. All televisions have a native resolution, that being the only resolution the television can show. While we have many different resolutions coming to the television, including 720X480, 1024X768, 1365X768, and 1920X1080, the television must process every signal and reformulate it to the native resolution of the television. That processing, done by the television is called scaling, de-interlacing, and upconverting, depending on exactly what kind of processing occurs.
That processing is often what determines the value of a television. A television that does a bad job at scaling or de-interlacing will usually not show a good picture, since it is rare that a television is fed its native resolution. Often you can see the same manufacturer listing the same size television with the same resolution and statistically they look very similar, but one may cost significanly more than the other. This is often due to the signal processing that the television does.
To make the processing more complicated, the set-top box that sends that signal, be it a cable box, satellite receiver, DVD player, Blu-Ray player, or video game console can often process the signal itself. When you let your DVD player send a 720p signal to a 1080p television when showing a 480p DVD, the signal is process multiple times, often causing multiple errors. It is difficult to determine exactly where processing errors occur, which cause artifacts to be shown on the screen, when multiple processing steps are being made. For this reason, and due to the value of television processors compared to set-top box processors, it is usually best to set any signal source to "native" when possible. This will keep the set-top box from doing any processing, it will just send the native resolution of the source material, and only the television will do any scaling or de-interlacing to the signal.
As most of us start to learn as we grow older, our eyes have limitations to the amount of detail they can see. This is just as true with television resolution. As the chart below shows, if you sit a certain distance from the television screen, your eyes will not physically be able to tell the difference between a 720p signal and a 1080p signal. This is accurate for most everyone, though there may be a few people with sight that is beyond the abilities of the common person.
The above chart gives a representation of screen size, viewing distance, and resolution needed. The chart tells us a few things. If you sit drastically close to a television, 1080p is something to consider. If you are considering a 32" television, however, you need to set closer than 5 feet from the screen in order for a 1080p television to be visably better. Since most people always sit further than 5 feet, 720p is usually all anyone needs for a 32" television.
The limited amount of 1080p content offered means that the decision to buy a 1080p television can be difficult. If you buy an entry-level 1080p television with a cheap processor, bad deinterlacing or scaling/upconverting can be disasterous. If you buy an inexpensive 720p television, you will probably see more native resolution material being shown on the television. Limited processing power is going to be a detriment on any television due to the amount of material that requires the television to process it. Smaller televisions will show less of the processing errors than larger televisions. But larger televisions require the processing in order to create a 1080p picture from whatever the source shows.
Is 1080p necessary? Not in all situations such as 32" televisions or large rooms, but the larger the screen and the closer you sit, the more important it is to invest more money in a better television with more processing power.
If you have any questions or need purchasing advice, call me at NOLA Smart Wire and I will help you make the right decision.