The general assumption that progressive video is always better than interlaced, or that 1080i is a sign of a sub-standard piece of hardware, has been a topic of debate for several years. While the actual statistical difference between the two would indicate a clear difference on paper, the point that interlaced video is always at a disadvantage is actually quite inaccurate. To the contrary, interlaced video has several advantages over progressive, depending on what it’s being used for. In this article, we’ll take a brief look at whether or not the interlacing in 1080i poses enough of a disadvantage to make it inferior to 720p, a lower resulting resolution with progressive frames.
1080i camcorders were very common as HD capability became an important buying decision for consumers. Seeing the 1080i was enough to convince many would-be buyers to pick that product over one that shot at 720p. The reason for this is simple: 1080 is more than 720, right? Well, when it comes to interlaced and progressive video, there are some very big differences.
Interlaced video takes two source frames of a lower resolution and weaves them together in a way that creates a single high-definition frame. By taking video that occurs a fraction (60th) of a second after the first, the appearance of jagged lines and various other video phenomenon can be reduced considerably. In short, a 1080i video is comprised of video that includes 540 horizontal lines shot 60 times per second, with occurrence capturing either the even or odd set of horizontal lines out of a larger 1080 lined image. Every other frame is interlaced with the one before it, turning the 60 frames of 540-line video into a single 1920×1080 image that changes 30 times per second.
Interlacing can create the appearance of jagged edges or blurred images during times of motion. You might notice what appears to be an object sliced into tiny bits with every other slice appearing shifted slightly out of place. This is caused by the 1/60th of a second delay between one half of the frame and the other.
Progressive video, on the other hand, is one frame after the other. A progressive video shown at 24 (or 23.976) frames per second will play back as exactly that, while one shot at 60 frames per second will also appear as such. This means you can actually achieve a higher frame rate than you could with a video that is shot in an interlaced format, simply because the speed of capture isn’t being halved by an interlacing process.
File sizes for progressive video can be considerably larger. A few years back, capture cards and storage technology for portable camcorders and other devices was considerably slower. Because of this, the possibility of capturing 720p or 1080p video at a decent frame rate was limited, though the slightly smaller interlaced videos contained less information, and were easier to store on the go. The sensor required by the camera to capture a larger image (in a progressive format) can also pose a limitation as a progressive camera needs to have a full 1080 horizontal lines to capture the image as it exists. Some cameras upscale what the sensor picks up, resulting in a slightly blurry, pixelated, or noisy image.
So, is 720p Better?
For most people, and most television sets, 720p video is enough to recreate a very clear high-definition image without the required file size or bandwidth of a 1080p set. Interlaced video creates a number of possible issues during capture, editing, and playback. The advantage of having a larger physical image with slightly more detail than you would find with 720p should be taken into account. You’ll get a larger, sharper image with 1080i than you will with 720p, but motion lines and other interlacing artifacts can certainly cause a disappointing overall viewing experience.
Whether or not one is better than the other is up to the viewer. Not everyone notices the jagged motion lines in most cases, and a larger overall image can be a good thing in close-viewing or larger screen home theater setups. The video quality of a 720p video is sufficient for most cases, and a lot of people will have a hard time telling the difference between the two.