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  • What Exactly Is High Definition
The Vision Experience

The Vision Experience

What Is High Definition?


When is it considered HDTV? Why do they refer High Definition to so many numbers and letters like 720p, 1080i, and 1080p? What do those I's and P's stand for anyway? This section will help explain High Definition picture formats that we see on the market today. VXP is here to educate our customers of the differences from Standard Definition to High Definition.

Standard Definition


Before the arrival of HDTV a television was considered just a television too many consumers. There wasn't much thought put into it. You just had to choose how big you wanted it. Today we have to put more thought into buying our High Definition systems.  If you’re like me it’s hard to get excited about something that is confusing and hard to understand. You may find yourself saying "Why should I buy it if I don't know what I'm getting?"

To better understand High Definition or HD, is easier to understand what standard definition is first.

Standard definition is referring to a minimum resolution of a video that a broadcaster is required to meet and match in order for it to work properly.  There have been round table meetings with business owners and scientists around the world on this issue to decide what these resolutions standards should be. Today, what we refer and identify standard definition to the resolutions up to 480i and 480p.

So let’s first define what the 480 means. The “480” stands for 480 lines of vertical resolution. If you were to count the pixels (each little dot)  on the image on your standard TV from the bottom right corner to the top right corner you would count 480 pixilated lines  in that image.

The 480 lines of resolution arrive to your screen in two different methods. The first method is interlacing. This is the "i" in 480i. The second method is progressive scan. This is the "p" in 480p.   What's happening with "i” or "interlacing is that every other line of the image is drawn and then the remaining lines that were left out of the image are drawn in to fill in the gaps. Simply, half of the image is being drawn onto the screen in real time. Why do this? It takes less bandwidth to draw the lines of the picture this way. We can't see it being drawn because happening faster than the eye can see. But if you were to slow it down the video enough in real time you would see a  line of image drawn, a line of skipped, and then the next line drawn again.

Example of  "p" Progressive Scan and "i" Interlacing   


What's happening with "p" or "progressive scan" is that you are seeing the entire video frame by frame. The entire picture is always being drawn and therefore the image is always there. Think of a film strip at a movie theater going through the projector hood and pulling through 24 frames of a film per second. This speed of the of the images passing by the light brings them to life on the screen.  An image you see being shown in progressive scan emulates a film strip that shows 24 frames or images per second. Although with digital technology the amount of frames can be higher than 24 per second. For example you might see a number like 1080p30 or 1080p40. This last number after the "p" referres to the number of frames per second. If you were to freeze a progressive scan frame you would see the entire image and it would not be grainy. Progressive Scan is the way to go when showing fast moving sports or images because the entire picture is always there. That's why Fox and ESPN use progressive scan for their sports broadcasts.

View the two photos below of the same car moving at 15mph. The First group of photos was taken with a progressive scan camera and the second set of picture with a interlaced camera. You can see the clarity with the progressive scan.

Example of Progressive Scan


Example Of Interlacing


High Definition

In a way High Definition is like putting on a pair glasses that you never knew you had. For instance, you put in an movie you have seen a hundred times. Although with your new HD glasses it's like seeing it again for the first time. Why is that?

High Definition format is roughly twice the vertical and horizontal picture information of standard definition. With HDTV you are simply seeing an image with more area and better resolution.  HDTV's have a different aspect ratio referred to as 16:9. The aspect ratio of 16:9 is referring to a standard measurement. This measurement is a formula that implies that for every 16 units of width there will be 9 units of height. This is the reason that the appearence of an HD television is more rectangular than square. There are some 18 variations of HD, but the two main High Definition formats are popularly in use today is 1080i and 720p. VXP will explain 720i, 720p, 1080i, and 1080p since they are all High Definition formats.

We've previously explained in the standard definition section that 480i means that there are 480 lines of vertical resolution and they are drawn in an interlacing method.  We also explained that 480p is 480 vertical lines of resolution where the entire picture is being drawn by progressive scan method: What is 720i? What is 1080i? Not to invent the wheel again, but 1080i means there are 1080 lines of vertical resolution which are drawn in an interlacing method.

What is 720p? It means there are 720 lines of vertical resolution where the entire picture is being drawn in a progressive scan method.

What is 1080p? 1080p is the top of the line high definition format on the market. It has an amazing 1080 lines of vertical resolution. That’s is over twice the lines of standard definition. More lines mean more resolution. The entire picture is always there because it is being drawn in a progressive scan method. Now even though there are HDTV's out there that can support 1080p, no one is broadcasting in 1080p because of its requirements for very high bandwidth. But just like Standard Definition, 1080p will be supper seeded at some point by Ultra High Definition. In the mean time enjoy 1080p with video games, On Demand Movies, and Blu-Ray.