It has been a few years since 4k video resolution first showed up in consumer home theater markets. The first 4k video projector for home use was released in early 2012, but it isn't until now that 4k technology, and content, is becoming more widely available.
4k, UHDTV, and Ultra HD, all mean the exact same thing, more or less. 4k is short hand for 4000 pixels, the rough width of 4k video resolution. To make things more confusing, 4k is measured differently than 1080p or HD, which is the current video standard most consumers are familiar with. 1080p is measured height wise, meaning the image resolution is 1080 pixels high.
If you are still confused about what a pixel is, don't be. Anyone who has put their face too close to a picture (or painting) to see the small visible dots making up the image has seen pixels. That's all they are, tiny measurable bits of color that make up a digital image. So, the terms 4k, Ultra High Definition Television, and Ultra High Definition, all refer to a screen that displays an image that is about 4000 pixels wide. This becomes very important when screens start becoming larger, because those same 4000 pixels will need to stretch the entire width of your television whether it is 20 inches, or 70 inches wide. But more on that later.
Both the pixel height and width of 4K resolution is doubled when compared to 1080p HD. Our current 1080p high definition screens are 1920 pixels wide by 1080 pixels tall, whereas 4K TV screens are usually 3840 pixels wide by 2160 pixels tall. Thanks to the magic of multiplication that means the overall resolution (total number of pixels) of 4K is four times that of our current HD televisions! Having four times as many pixels in the same amount of space means that they are packed much more tightly, making the image sharper, more life like, and more capable or representing subtle variations in color.
Screen Size & Pixel Density
4K delivers the same amount of pixels regardless of the size of the screen being viewed. So, whether you are watching 4K video on a 20 ft movie screen, or a 20 in computer monitor the same amount of information is filling both screens. Smaller screens will have a much higher density of pixels for a given area because there is less total area to fill. The opposite is true for larger screens. If this concept seems confusing, think about painting a wall in a house. A small wall might take a half can of paint to cover, whereas a larger wall might take three or four cans. If there is only so much paint, it can only cover so large a wall before being spread thin. On the flip side, using all of the paint on a small wall proves wasteful because after a couple of coats it won't look any better. The same is true for pixels per inch on a video screen. Too few pixels and the image starts to degrade. Too many pixels won't cause the image to be worse, but after a certain point they won't cause the image to look any better either. Those familiar with Apple computer products may have heard the term "Retina Display" before. This is Apple marketing speak for a pixel density that reaches the highest level of quality the human eye can determine. Or, in our analogy, Apple is saying that they've provided you with just the right amount of paint without being wasteful. Based on this information, 4K video is most beneficial on larger TV and Movie screens, or in a situation where the viewer is very close to the screen (like a computer monitor). 4k video increases the pixel density (or pixels per inch) of a given screen, allowing screens to become larger while still increasing image quality.
Content, Content, Content!
For 4K to work, it isn't enough that the screen can display 4K resolution. The movie, TV show, or video being displayed also needs to have been created in at least 4K. For home theater enthusiasts, this means that their physical media (like Blurays) or streaming services (like Netflix or VUDU) need to support 4k. So without additional content, it might appear that having a 4K television won't do much good. Fortunately, this is only half true. When buying a top end ultra high definition television, 4K is only one of many improvements over older sets. Think of 4K as a nice feature, but not necessarily the only selling point of a new UHD TV. It's nice to have, and consumers will be able to take advantage of it as more content becomes readily available. It is not however the only benefit consumers will be receiving when upgrading their TVs. The best 4K TVs also happen to provide enhanced color reproduction and advanced features like LED local dimming. These improvements are definitely noticeable regardless of the resolution of content being displayed.
If you are buying a TV solely because it is advertised as 4K I'd slow down a bit. First, you want to make sure that the screen is large enough, or you will be sitting close enough, to take advantage of the enhanced resolution. Next, you'll need to determine if you have access to 4K content to view on your new TV or projector. Amazon and Netlflix are already streaming some content in 4K, Sony has a dedicated 4K movie streaming service, DirecTV is upgrading, and physical 4K media (like Blurays) are already in the pipeline source: Engadget.
Ultimately, if you want to upgrade to a new high end ultra high definition television, and 4K just happens to be one of many new features included, don't hesitate just because there doesn't appear to be much 4K content available, because it is on the way. New screens also showcase some nice technology you can immediately take advantage of that marketers aren't pushing just because it doesn't fit into two characters: 4K.