Why Dark Video Is A Terrible Blocky Mess

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“Dark doesn t look very good these days and i m really sorry if you you re one of the nlucky ones. Who s never noticed this because now i it out now i artificially increase the brightness non the dark parts in this video. So you can see what the shadows behind me nactually look like now you ll notice in movie. Trailers in dark scenes in even prestige television in youtube videos where there are nnice calm.

Gradient backgrounds. You see this dreadful colour banding. There are three reasons for it and the first is that nthere aren t enough colours all right. I ll turn the lights on in most modern digital.

Video there is a grand total of about n167. Million possible colours and that number comes from how your screen works when you watch a video nyour phone computer or tv takes that compressed digital signal nthat s being sent to you and it converts it into instructions those instructions go to the screen. Which changes the brightness nof each of the millions of red green and blue lights nthat make up your screen up to 60 times a second perfectly. It s incredible technology that nwe just take for granted.

But those little lights can t be nadjusted to any brightness the simplest digital signal nwould just tell the screen whether to turn each light on or off each instruction would take a single bit na single one or zero. So for each pixel neach combination of red green and blue that gives you eight possible colours two times two times two. Which doesn t look great. So okay.

Let s add another bit for each colour two bits gives us four options for each light. Noff dark sorta..

Bright and completely on now. We ve got four times four times four n64 colours. Still doesn t look great for a modern screen nyou. Need eight bits for each pixel.

So. You ve got 256. Shades. Each nof red green and blue.

Which gives you those 16 million ncolours that you re used to that ought to be enough right it seemed to be when the standards were written and to be fair every bit you add means more data to transmit nand more expensive equipment. It seemed like a pretty good compromise. Nat. The time professionals like people working nin digital cinema.

They go further nthey might use ten bits for each pixel. Giving them about a billion ntotal. Possible colours instead. And you may well have a fancy screen that ncan show those more precise billion colours.

But the picture quality is determined by the nweakest link in the chain. A ludicrously expensive hdr monitor isn t ngoing to fix the colour banding on that regular youtube video anyway..

It was decided that 256 shades neach of red green and blue combined. However you like nthat should be enough for most people and for almost. Everything it is but at full. Resolution this video is 1920.

Npixels. Wide. And there are only 256 shades of green. So if i have a green gradient across nthe whole video.

Even if you use every single shade of pure ngreen that s possible on this format. Then you re still going to have a colour band nevery seven or eight pixels and if everything s much darker than that suddenly you only might have half a dozen ndifferent shades of green available across the whole picture. Even if you re using a bit of red and blue nin. There as well there just aren t that many navailable dark colours.

But if you ve got nplain. Bright background. Why doesn t that have ncolour banding all over it well the second reason is nhow human eyesight works. There is colour banding all over this video nright now if we take a sample of the bright gradient nbehind me and massively increase the contrast you can see it s there nbut normally it s invisible and that s because while the absolute difference nbetween.

Two bands is still the same the relative difference is tiny. It s the same reason that this chart looks na lot closer than this chart going from 201 to 202 nfeels like a tiny change..

But going from 1 to 2 is a doubling even though in both cases. The absolute change is the same one we perceive one as being nbigger than the other. But even if you don t have enough colours you can break up gradients. Another way nyou can use dithering instead of going from one colour to another nat a line you can steadily transition from none to the other you can make the boundary fuzzy.

So that from a distance nthe colours appear to blend and if you re filming a real life scene nthen that ll happen in camera the natural light and the noise in the signal nand. The sensor will do that for you and it actually works really well nit more or less solves. The problem. But it won t look like that here and that brings me to the third reason ncompression a raw hd video uncompressed needs somewhere around na gigabit per second of data.

Even if you have an internet connection that ncan somehow support streaming all that it s incredibly wasteful and expensive to nuse all that data so every streaming service nyoutube. Netflix. Everyone uses lossy compression. A program called an encoder takes a nmassive high quality video file.

And then throws away fine detail to save data the more the video is compressed nthe worse it looks. But it ll work on slower and slower connections and it ll be cheaper and cheaper nto run your streaming service. But at some point. The viewers are going to notice that the picture ndoesn t look great.

But the encoder the compression software nis written by very clever people and it works out which bits of the scene. The viewer is probably ngoing to be interested in and puts..

Most of its effort into making nthat part look good. And that s usually a bright sharp part nof. The scene something well lit and in focus and probably the bits that are moving now. There are exceptions.

Where there s some slow menacing threat nout of focus in the background. But for almost every scene nif. It s dark or out of focus. Chances are the director and the viewer ndoesn t care about it so the encoder doesn t care about it either.

If there are only fifty kilobits. Fifty thousand ones and zeros available to ndescribe each frame of video. Then the encoder will make sure nthat. Most of those are spent on where the viewer s nlikely to be looking all that dithering all the fancy stuff nin.

The background too expensive smear it out into just big blocks nof solid colour. No one ll notice and we won t unless. It s also very dark at which point. ” .


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