For all practical purposes, there is no appreciable difference between 1080i and 1080p picture quality. The distinction is largely beyond the human eye’s ability to pick up, even on the largest HD televisions. Furthermore, as of early 2008, no television broadcasts are available in 1080p, and the only practical places where you can find it are on HD DVDs, Blu-Ray DVDs and certain high-end computer monitors. You can differentiate between 1080i and 1080p picture quality, however, if you understand the distinctions within the technology itself.
1. Learn what the “i” stands for in 1080i: it means “interlaced,” which refers to the way in which the number of pixels are displayed. The pictures consist of 1,080 horizontal pixels, but in an interlaced television, the camera samples only half of them at any time: the odd-numbered pixels are sampled in one scan, and then the even numbered pixels in the next. Each scan lasts just 1/60 of a second, so when they are “interlaced” together, they give the nearly invisible impression of a unified image.
2. Discover what the “p” stands for in 1080p: “progressive.” Unlike 1080i, the 1080p image shows all 1,080 horizontal pixels at the same time. This cuts down on incidental side-effects of 1080i, such as line twitter and combing, which are usually invisible to the naked eye but can have a slight effect on the picture quality.
3. Examine the images on the biggest TV you can: 50 inches or 55 inches at the minimum. If you have one of your own, fine, but it might pay to visit a local electronics store and ask for a demonstration of the differences between 1080i and 1080p.
4. Check how your system de-interlaces a 1080i signal. With the exception of a few older models, all entertainment systems will de-interlace the signal. Cheaper ones will simply drop the image quality to 540 pixels, while top-of-the-line models will “properly” de-interlace the image to a full 1,080 pixels.
5. Examine images that involve objects moving across the screen on systems with cheaper de-interlacers and compare them to ones de-interlaced to 1,080 pixels. The still image in the 540 pixel version will look blurrier or exhibit a slight twitter, matching the moving image. With a 1080 image, only the moving object will twitter, while the stationary objects will look much sharper–allowing you to differentiate between them.