Our televisions aren’t perfect. As much as we would all like to have that “looking out a window” picture quality 100% of the time, often times it’s not possible. In some cases, it’s because fast action can’t be captured and compressed enough to be transmitted live. In other cases, the culprit is streaming video (like Netflix and Hulu) that is designed for lower-speed connections. This is less of a problem than in years past since many of us have upgraded to higher-speed connections, but during peak times, it’s still not always possible to get a full-bandwidth stream, and we tend to think that something is better than nothing.
Today we take a look at pixelation. if you look at the image above, you’ll see that it is made up of large blocks of consistent size. This is exactly what is meant by pixelation. Pixelation happens most often because when motion happens too fast, compression software isn’t able to keep up and there is only time to process a very blocky version of the image. Pixelation usually clears up when the picture slows down.
A lot of people confuse pixelation with macroblocking. We discussed macroblocking in a previous article and it’s easy to see why they get people confused. Both pixelation and macroblocking give you a blocky picture. With macroblocking the affected areas are all of similar color and the blocks can be different sizes. With pixelation all the blocks are the same size and the problem is usually associated with fast motion.
As with other compression artifacts, the problem comes from the video source. An HDTV picture is just too massively big to be sent uncompressed. As we’ve said before it’s possible to compress an image up to 80% with barely-noticeable differences. Beyond that there is always some tradeoff in quality when you reduce the size. As you get to the point where you are compressing the image 95% or more (as happens with streaming video) artifacts like pixelation are bound to happen.
Pixelation is still common with live events that have fast motion and concerns about pixelation have driven broadcasters to invest millions of dollars into super-high-end encoding systems for 4K. It simply wouldn’t do to have the picture devolve into blocks the size of your thumb when the action really gets going.
When it comes to traditionally delivered TV, pixelation is almost unheard of except in live events. Careful, slow encoding can almost always eliminate this artifact. However, it still can be seen in streaming, especially from “second-tier” streaming providers like TubiTV and PopcornFlix that don’t necessarily take the same time to encode their streams as better known competitors like Netflix and Hulu.
By the way…. the correct spelling is “pixelation” because the image has visible pixels (picture elements. You may have seen it spelled “pixilation” but that’s something completely different: a technique combining stop-motion photography with animation.
Image courtesy of Barry Blanchard.