Believe it or not, the image above is all the same resolution, from one end to another. But your eyes aren’t deceiving you… there’s a definite difference in quality between the part with the grey cat and the part with the white cat. This a perfect way to show that high resolution doesn’t always mean high quality.
Of course, the people who sell you TVs and streaming devices would really prefer you not know that.
Digital signals, when you come right down to it, are nothing but ones and zeroes, and they can be manipulated a lot of different ways. You can take an image with a resolution of 1920×1080 (the resolution of most HD programs) and manipulate it so it takes 2.2 gigabits to show a second of programming, or you can tweak those numbers so it takes only about 3.6 megabits. I’m talking about a 90% reduction in size. It’s done with fancy mathematics and the expectation that you won’t really notice what’s missing.
The size of a digital HD “stream” can be controlled by cutting all sorts of picture information out and by using advance compression that puts errors into the signal that you (hopefully) won’t see. If the signal is compressed too much, you get something like the image on the right side. If it’s done properly, you get something like the image on the left side.
It’s important to know about the difference between resolution and quality. You’ll notice that streaming services like Netflix advertise their resolution (even going up to 4K) but they don’t advertise the size of their streams. That’s because Netflix’s HD streams can be heavily compressed and even though they are still technically HD, they can’t compare to the image quality you’ll get from DIRECTV or over-the-air broadcasting
In fact, over-the-air broadcasting such as you can get from a TV antenna is going to be the best quality HD you’ll get, short of a Blu-ray disc. That’s because the relatively simple math used for over-the-air digital signals can only compress them down to about 19 megabits per second. Without excess compression, over-the-air signals look sharper and cleaner than the same signals on cable. In fact cable companies and streaming companies (like Hulu) actually get their signals using antennas then decompress and re-process those signals, taking quality out so that the result can never be as good as the original..
And then of course Hulu will tell you that their signal is 1080i, the same as over-the-air broadcasts, but they won’t talk about quality. That’s simply because they can’t talk about quality with a straight face.
With 4K, it’s even more of a problem. A 4K image is between 4 and 8 times larger than an equivalent HD image, and you would need internet speeds higher than 500 megabits per second to really be able to stream it or get it over the air, if advanced compression wasn’t used. Even with advanced compression, it takes a 50 megabits per second signal to get really acceptable quality; anything less and (believe it or not) your 4K picture could look worse than an HD one. This is the problem that Netflix and other companies streaming 4K are facing — their quality just isn’t that good. On the other hand, DIRECTV has solved this problem with its live 4K programming by simply allocating 6 times the space for each 4K channel that it allocates for each HD channel on its new satellites. That’s one way to do it!!