720p vs. 1080i HDTV

Is 720p vs 1080i worth worrying about? Yes and no. If you’re a consumer looking for a new TV, you can happily ignore the 720p versus 1080i debate because all TVs that are described as HDTV or HDTV Ready must support both formats.

NOTE: However, you should be aware that many TVs that support 1080i have fewer than 1080 lines and therefore downscale the 1080 signal. That’s not a big deal, as even 1080i downscaling is way ahead of a normal NTSC signal. It’s worth keeping in mind that more expensive HDTVs tend to have better scalers than cheaper ones, and this can be a problem.

However, for broadcasters it is a live issue. Should they stream 1080 lines of interlaced video or 720 lines of progressive scan? They could just transmit two signals, one in each format, but that would consume a lot of bandwidth and be very expensive for very little gain.

To answer the question, it is important to understand the difference between 720p and 1080i. A 720p signal is made up of 720 horizontal lines. Each frame is displayed in its entirety on the screen for 1/30 of a second. This is known as progressive scan (hence the ‘p’). The quality is like watching 30 photographic images per second on television. A 1080i signal includes 1080 horizontal lines, but not all lines are displayed on the screen simultaneously. Instead they are interlaced (hence the ‘i’), ie every other line is displayed for 1/60th of a second and then alternate lines are displayed for 1/60th of a second. So the frame rate is still 30 frames per second, but each frame is split into two fields, which your brain then subconsciously puts together.

Most of the time, interlacing works fine, but for fast-moving images, such as sports like baseball and hockey, it can cause problems that manifest as a “passing” effect on the screen. Progressive scan signals do not have this problem and are therefore better suited to sports.

ESPN puts it this way: ‘Progressive scan technology produces better images for the fast-moving orientation of sports television. Simply put, with 104 mph fastballs in baseball and 120 mph shots on goal in hockey, progressive scan technology’s line-by-line baseline better captures the fast action inherent in sports. For ESPN, progressive scan technology makes perfect sense.’

Bottom line? For us as consumers, 720p vs 1080i is not a debate worth worrying about, so you can relax and focus on all the other criteria on your list when shopping for your next HDTV.