Michael Koby

There are several things to consider and look at when you are purchasing a high definition television.  You’ll be bombarded with all kinds of numbers, specifications, abbreviations, and brands.  There are three main concerns when you purchase a HDTV and they are resolution, seating distance, and display technology.  Today I want to look at the concept of resolution and touch on seating distance. 

Considerations to Keep in Mind

Just so you know, there is no hard and fast rule on display resolutions.  There are factors that will determine exactly how much detail you can see in the image your television produces.  Some of these factors include seating distance, eye sight, and even viewing angle.  When doing research for purchasing a high definition television, you will some charts that help you determine what size TV to get at various seating distances (example HDTV Distance Chart [PDF]), use these as a guide rather than a hard/fast rule.

720p versus 1080p

The numbers refer to the resolution of the image being displayed on the television.  What is resolution?  It is the number of pixels on the screen.  A pixel is a little dot of color that is part of a larger picture.  The general rule of thumb is that the more pixels you have in a certain amount of space, the better the detail you will see.

What do these numbers mean?  You will see them a lot so it is important to understand exactly what they are and what they mean.  The most basic definition of what these mean is the number of physical lines on the screen.  So 720p means 720 actual lines on the screen progressively (we’ll get into that a little later) where as 1080p means 1080 lines on the screen.  So basically the 1080 resolutions (both “p” an “i”) are going to give you better detail in the picture you see on the screen.  Both however will give you a better image over your current CRT television.

So which one is better?  You are probably going to spend a good deal of money on this high definition television set, so you’ll want to get the best deal you can.  When deciding on what television to buy knowing how far you will be sitting from the television on average.  For example, with a 52 inch screen you’ll notice the detail difference for a 1080 resolution at around 6 feet (remember these numbers don’t take eye sight or viewing angle into effect).  But with a 720 resolution you’ll see the detail at around 10 feet.  Remember that I said that those numbers aren’t “sure things” and your experience may vary.

But a 50 inch 720p HDTV can be had for less than a 1080p set (usually around 500 dollars less), so if your room has seating that’s 10 feet away and moving it closer is just not an option, then a 50 inch 720 resolution television will serve you better than 1080 television that is the same size at 10 feet away.  This is not to say that you wouldn’t notice any of the 1080 detail at 10 feet away, just that you will lose some of it in distance.

Extra Note – Some people will tell you that you won’t notice the 1080 difference until you get to screen sizes above 50 or so.  This depends again on your vision.  My friend has a 42 inch television and I can tell the difference between 720 and 1080 with my glasses on, with them off however I can not tell the difference.  Just something to keep in mind when looking at televisions in the store.

What Does that “p” Stand For

As you look at HDTVs in stores you’ll notice that some say “1080p” and others say “720p” on their descriptions.  You’ve probably have asked yourself (or a sales person) what this means.  The “p” means “progressive scan” and it is how the signal is delivered/processed.

There are two major kinds of scanning technologies available on most HDTV sets: progressive and interlaced.  When a signal is progressive, that means that the all the lines of a single frame are shown.  So if you have are watching 30 frames a second progressively, then you will see all the lines of each frame.  When a signal is interlaced (like most regular TV) you see the lines from two frames together rather than in a single frame.  This means that you are actually seeing parts of two different images rather than a single image.  When looking at an interlaced signal you are see what is called fields and two separate ones at that.  You will using see all the even lines of one field and all the odd lines from another field.

So overall, a progressive image is better since you see all the lines of a single frame and you see them as the frames move so you see more detail as a scene progresses.

Some will argue that it is really hard to tell the difference between progressive and interlaced, and they are right in most cases.  However, when you see interlaced content on occasion mouth movements can not sync up with the audio (this is because parts of the mouth might have lines in it that are from one field and the other part from the other field), images can look “off” on occasion if there is a glitch in the signal, and sometimes images can become disjointed.  Overall though, you’ll probably not notice the difference.  Where the progressive part really comes in handy is during action sequences, the scenes will “flow” better due to the nature of a progressive signal.

Seating Distance

Lets touch on seating distance real quick since it’s a really quick topic and doesn’t really need its own post.  I posted a link to a chart that shows about where the optimum seating distance is for various resolutions on different sized displays.  Again, these charts don’t take into account your eye sight.  If you have better eye sight you can sit further and still see the detail, worse eye sight and you’ll need to sit closer.

However, seating distance can play a huge role in how big a television to buy.  For this, I recommend Amazon’s formula.  While not exact it’s the easiest to do to get an idea on what size television to buy.

Minimum Size = Viewing Distance/3

Maximum Size = Viewing Distance/1.5

Like I said it’s not a hard formula to perform and it can help you figure out what size television to buy.  Bigger is generally better so the closer you can get to that maximum viewing size, the better you’re probably going to feel about your purchase.

Next Week

Next week, we will start look at the different display technologies with a heavy focus on LCD and plasma technologies.  I’ll probably do those in a single article and spend a second article looking at projectors and DLP televisions since those two options aren’t as popular as LCD and plasma but are available (projectors will become more popular as prices drop).