EDTV vs HDTV: a quick primer

Nick used our contact form to ask about the difference between EDTV and HDTV: "So what's the deal with ED vs HD?  I'm not aware of what ED actually IS.  Can you guys help?"

I think we can help with that, and thanks for the question, Nick! There's plenty to talk about here, but we'll give you the basics that you need to know. ED and HD are both considered DTV (or digital TV). However, not all of the 18 approved DTV formats are HD, which is where confusion starts to set in. Just because a set or signal is "digital", that doesn't mean that it's "high-definition".

EDTV is comparable to DVD-quality, or what is called "480p". "480" indicates the horizontal lines of picture resolution, while the "p" stands for progressive. Progressive means that the entire picture is drawn at one time, which is the opposite of interlaced (or "i"). Interlaced pictures draw half of the screen at one time; first the even numbered lines, then the odd numbered lines. This is done so quickly and so many times per second that you can't see the lines drawn at different times.

Here's where the comparison gets a little tricky. There's only one Extended Definition (ED) format; the 480p display that we mentioned. HDTV, or High Definition, has multiple formats that qualify as HD. The most common formats broadcast today are 720p and 1080i. Using some of our definitions above, 720p means 720 horizontal lines of resolution displayed progressive (or drawn at the same time). 1080i shows 1080 lines drawn in an interlaced fashion.

If you do a little math with some common format examples, you can begin to see the difference between ED and HD quite clearly (sorry, we couldn't resist that one!):

Format        Common Resolution        Pixels
480p            720 x 480                          345,600
720p            1280 x 720                        921,600
1080i           1920 x 1080                   2,073,600

The simple math shows that an ED, or 480p, display provides only 35% of the number of pixels as the lowest common HD resolution. Typically, more pixels mean a greater level of detail; the same principle applies to megapixels and digital cameras.

Forgetting the math at the moment, we'll make one suggestion. Go to your local television retailer and ask to see the same HD program on an ED and an HD television set. Also ask to see a DVD on both sets; some of the newer DVD players actually upconvert the 480p signal to 720p or higher. Remember, the math is one thing, but let your eyes be the judge!

Thanks again for the question Nick, and we hope this helps. If you have a question, tip or comment, don't be shy. Use our contact form and we'll see if we can help you navigate through the world of HD!