The “HD” of HDMI means High Definition (AKA: High Def). But, what exactly is that? It is synonymous with top quality. The meaning is not really black and white .. yeah, it is more like a shade of gray. It can also be used in different contexts: sound, video, broadcast, antenna, cable, display, and so forth. For this entry I will focus on display as in the case of a HD TV and to some extent, HDMI cables.
Fundamentally, in the context of displays, High Definition simply means higher than standard resolution for video. Think of a TV or a computer monitor as a rectangle with a certain number of Horizontal and Vertical lines (or pixels). The resolution of the display is determined by the number of lines in both directions. The more lines there are, the higher the display resolution.
So, what is standard resolution? Actually, it depends on where you are. From the European developed PAL and SECAM system, it is 576i lines. For the American National Television System Committee (NTSC), it is 480i.
As a general matter, the characteristics of a HD display is captured with the following 3 properties:
Frame Size – is defined as the number of Horizontal pixels by number of Vertical pixels. For example, one common Frame Size is: 1280X720
Scanning System – usually represented with a symbol of “p” or “i” for Progressive and Interlaced scanning respectively. These are technical sounding terms, but they are pertinent to the understanding of different types of displays. Progressive scan is a way of displaying and manipulating images in which all the lines of each frame are drawn sequentially. Basically, it is like reading a page of a book from the upper left hand corner to the lower right hand corner without skipping a line. The benefit of this way of scanning is that motion appear smoother and more realistic. It is also better for up-scaling to a higher resolution. The only negative about this method is that it requires a higher bandwidth which has many implications all of which broils down to higher cost in the final analysis.
With Interlaced scanning, odd lines and then even lines of each frame are drawn alternatively. However, the characteristics of the display material and the responsiveness of the human eyes create the perception of a continuous image. This is the method that is used in most analog systems. The benefit of this method is that it requires less bandwidth. In fact, ½ as much as compared to the Progressive scan method. The drawback is that the picture quality is not as good.
Frame Rate – as the name suggest, is the number of video frames per second. For most modern HD TV this is on the order of 60 to 120.
Sometimes all three properties are specified in this format:
[Frame Size][Scanning System][Frame Rate]
However, more times than not, some of the details are dropped because they are implied. So, in marketing literature and commercial naming you will most likely see something of this form: 720i, 720p, 1080i, 1080p
In this form, only the Vertical Resolution along with the Scanning System is specified. When you go to your favorite electronic store or shop online, this is the form that you would see.
For connecting HDMI enabled devices to High Definition (HD) displays with resolutions of: 720i, 720p and 1080i a Standard HDMI® Cable should do the trick. However, for a 1080p display a High Speed HDMI® Cable is recommended.