What's Up With This 2K and 4K Ultra High Definition?

You don't have to worry about your television's becoming obsolete because of 2K. You can ignore 2K for now. The difference in resolution compared with HDTV is very small and most folks cannot tell the difference unless they know what to look for and look hard to find a difference..

By now we all know about Full HDTV (1920 x 1080 pixels) and 720p HDTV (1280 x 720 pixels).

But there are some newcomers called 4K, UHD, and 2K. Standards for the 2K and 4K formats have been developed by a group called Digital Cinema Incentives representing major studios including Disney, Universal, and Warner Bros.

The 2K format is actually a family of formats used primarily in commercial movie theaters as the modern successor to 35mm film. It gets its name from the horizontal pixel count of 2048, which number computer experts refer to as 2K. (The "K" stands for "kilo" (thousand) where in the context of computers the magic number is 1024, or two to the power ten, instead of an even thousand.).

Depending on the application, the vertical resolution ranges from 1536 pixels (used with a 4:3 aspect ratio screen) to 1080 pixels (most commonly used for movies). The 1080 pixels vertically is coincidentally the same as used for Full HDTV.

Many movie producers doing a shooting in the (common) 1.85:1 aspect ratio continue to use that instead of the very close 1.78:1 (16:9) television standard. Although it is not an exact match, 2048 pixels across paired with the TV standard of 1080 pixels down gives excellent results with the 1.85:1 (approx. 17:9) aspect ratio.

The exact standard for 1.85:1 2K movies is 1998 x 1080. Cameras may or may not capture, production may or may not utilize, and theater projector masking and mattes may or may not frame the entire 2048 pixel width that gives an extra 20 pixels on each side.

A bit of cinematography history with some oversimplification: The 35mm film frame for motion pictures (not for still cameras) has an approximate 4:3 (more exactly 1.37:1) aspect ratio. Movie producers may use a portion (full width, partial height) of the film frame for shooting a wide screen movie with projection "as-is" (the term used is spherical or flat). Or they may use a special camera lens (called anamorphic) that stretches the image to fill the entire film frame and the theater uses a complementary anamorphic projector lens to re-shape the projected image to the correct proportions and desired wide screen aspect ratio. Similarly, digital "filming" may use (for example) a 2048 x 1080 subset of a (normally 4:3) 2048 x 1536 video frame for a wide screen movie requiring no "anamorphic" processing. Most movies in aspect ratios greater than 2.00:1 are shot anamorphically to better utilize the (4:3) film frame. So anamorphic digital shooting making more utilization of the 2048 x 1536 video frame remains common. The finished movie has to be available as downconverted to 2048 x 1080 for projectors of that resolution.

Currently there are no TV shows or consumer video disks in the 2K format. Some 2K content including as 2048 x 1536 pixels is available from Netflix and other on-line subscription services, or downloaded from private Internet sources..

It must be remembered that a digital (non-cathode ray tube) TV set or monitor or projector has just one native resolution. We already mentioned the 2048 x 1536 4:3 aspect ratio, 2048 x 1536 16:9 (or 17:9) aspect ratio, and 2048 x 1080 16:9 aspect ratio resolutions. U.S. HDTV uses the 1920 x 1080 (and 1280 x 720) resolution in 16:9 aspect ratio. So scaling  (upconverting or downconverting) of program material to match the screen resolution and best fit the screen will always be needed and fortunately this can be done with hardly noticeable distortion.

The 2K format as used by movie studios and commercial theaters also has higher quality than HDTV. For example 2K as currently used has 1024* to 4096* gradations (10 to 12 bits digitally) of color compared with HDTV's 256* gradations (8 bits) known as "Rec. 709." Here, too, the computer supporting the TV set or projector can convert between 2K and HDTV. Even a critical viewer would find it hard to tell the difference between 2K and HDTV on an above average size (60+ inch) direct view TV set if such a set were to be manufactured to 2K specifications. A 10 bit standard referred to as "Rec. 2020" is starting to take hold for TV sets while 12 bits might still be used for production.

Also, for television and video disks, every 2 x 2 block of pixels share the same coloration (hue). The pixels within a given block can come individually as, for example, lime green and olive green, but not come as green and yellow. Movies as supplied to theaters can (not all do) give each pixel its own color. This is not easy to see. The human eye does not readily notice errors in fine color detail, and the data compression used in preparing the movies for transmission and downloading (or making of video disks) adds a comparable amount of additional fine detail color distortion including what is referred to as mosquito noise.

The same processing in the TV set that generates 120 frames per second from the incoming 24 fps or 60 fields per second or 60 fps video may blend and smooth out color transitions from the rigid one hue per 2x2 block of pixels.

For you math experts, 2048 x 1080 2K has 2211840 pixels while 1080 HDTV has 2073600 pixels while for an increase of 6-2/3 percent which this writer would consider "slight". Most folks won't go out and buy a new TV set for just a seven percent improvement.

Now On To the 4K

Today (2017) there are a lot of"ultra high definition" or "UHD" TV sets in the stores. They have (or should have) twice the number of pixels across and twice the number of pixels down  compared with Full HDTV. That is, UHD is defined as 3840 pixels across by 2160 down. Although the "4" in 4K does not stand for this, you will notice that there is a total of four times the number of pixels (8294400) in UHD compared with the 2073600 pixels of Full HDTV (1920 x 1080 pixels). The 4K does not stand for megapixels. While both 2K and Full HDTV, are rated as two megapixels, 4K has eight megapixels.

Meanwhile there exists the real 4K family of formats including the 4096 x 2160 pixel format optimized for the approx. 17:9 (1.85:1) aspect ratio movie. Up until now (2012) movie producers have considered it desirable to shoot and produce movies digitally using a resolution somewhat higher than what the finished movie will be shown as or sold to the public as. Twice the resolution horizontally and vertically (i.e. 4K) is one such format used for shooting  movies to be shown in HDTV and 2K formats. The 4096 x 2160 4K format used for both shooting/production and showing is gradually taking hold in the commercial movie industry, held back only by the added cost to theaters for upgrading projectors and equipment. Movies shot in 4K would be downloaded to theaters in the version (2K or 4K) the theater desires, as well as downconverted to 1920 x 1080 resolution for Blu-Ray video disks or television broadcast.

TV sets labeled or advertised as 4K should have 4096 pixels horizontally. Most consumer grade models will accept all standard video resolutions including composite 480i, and upscale the video to fit the screen.

As is the case with 2K versus Full HDTV (and also versus 7200p HDTV), some processing is needed to  fit a movie or program of one resolution on a screen of another resolution. The same techniques would be used. For example the picture may be expanded, shrunk, or stretched slightly and/or the edges trimmed off and/or the picture not quite filling the screen. In the case of 4K and UHD, unless the processing was particularly poor, the average viewer would not be able to tell the difference.

The same dilemma of black bars (letterboxing; pillarboxing) versus cropping of the edges of the picture will exist with 4K as with 2K and old analog video of different aspect ratios. As with 2K, each TV set has only one native resolution. We expect that the following screen resolutions will be offered:

16:9 UHD 3840 x 2160
16:9 and 17:9 4K 4096 x 2160
4:3 4K 4096 x 3072 (probably for projectors only, not direct view screens)

Meanwhile the movies and other programs will each be produced in one of a few dozen different formats including the five immediately above, but most likely using cameras in one of two formats:

17:9 4096 x 2160
4:3 4096 x 3072 with optional 16:9 anamorphic lens

At this time we are not able to speculate whether most UHD (3840 pixel wide) TV sets will crop the edges of full 4K material (a 7% loss) versus downscale the material to 3820 pixels wide, or whether most 4K TV sets will display UHD material as-is with some unused screen area at both sides versus upscale that material to 4096 pixels wide. Video purists will continue to object to cropping of the edges of the picture. But each time video is upscaled or downscaled (upconverted or downconverted) generation loss occurs.

As with 2K, some 4K TV sets may skimp on quality, for example using HDTV technology (including 8 bit e.g. Rec 709 color) instead of the 10 bit Rec. 2020 color of the evolving 4K standard.

Some experts are recommending that consumers already owning an HDTV set not upgrade further until sets with the full 4K (4096 x 2160) resolution and 10 bit Rec. 2020 color and HDMI version 2.0 become available. Earlier HDMI 1.x versons cannot carry the quantity of data required by 4K.

For simplicity we have not discussed other movie aspect ratios of which there are several. For 4K, production will use the same techniques as 2K including, in many cases, using a subset of the pixel field (for example  4096 x 2048 pixels instead of 4096 x 2160 pixels for 2.00:1 aspect ratio) or using different anamorphic lenses. Also for simplicity we have pretty much ignored slight differences in pixel counts such as 3996 x 2160 instead of 4096 x 2160 for the true 1.85:1 aspect ratio.

What About (Or What Is) 1.3K Format?

This is 1280 pixels wide, and includes the HDTV 720p (1280 x 720 pixel) format. Some commercial theaters have obtained and shown movies digitally in 1.3K.

Other Notes

We use the term "TV set" loosely here. A TV set's primary purpose is to receive television broadcasts, none of which are in 2K format let alone 4K.

Note that a pixel field, for example 1920 x 1080; (raster if you insist) has no inherent aspect ratio. Aspect ratios are assigned by rules and conventions. One may use the term "anamorphic" to refer to situations where the pixel positions as as finally viewed are not square because the intended aspect ratio does not equal the horizontal pixel count divided by the vertical pixel count.

Horizontal resolution refers to the maximum number of upright lines, or dots in a row, that can be distinguished within a given distance. Vertical resolution refers to stacked lines, or dots in a column. For TV and video, a black dot and a white space next to it count as two lines. For film, a black dot and a white space next to it count as one line but are nowadays often referred to as one line pair. "Lines of resolution" and pixels are not the same thing although under ideal conditions they can be equal. Why they differ is explained as a "Kell factor."

* While so many bits stands for so many different values or gradations, such as 256 color gradations for 8 bits, in actual practice the number of gradations is a little smaller due to some values' being reserved for special purposes.


Last updated 7/7/14

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