Since 4K is replacing HD in our home, manufacturers reveal some interesting marketing jargon such as "Ultra HD Upscaling" (UHD). However, upscaling is not a unique feature ̵
All TVs are upscaled.
Upscaling means that low-resolution content fills the entire TV screen. Without this feature, a low-resolution video will occupy less than half the screen area. This is a typical feature of all TVs. Even 1080p televisions had it – they could scale up 720p content and view it in full screen on a 1080p screen.
Thanks to UHD upscaling, your 4K TV works like any other. Lower-resolution content can be viewed on the entire 4K screen.
Upscaled 1080p content on a 4K screen often looks better than 1080p content on a standard 1080p screen. But upscaling is not magic – you will not get the sharp picture you would get from true, native 4K content. How it works:
Resolution exists on a physical and visual level
Before we begin upscaling, we need to understand the concept of image resolution. At a glance, it's a relatively simple concept. A picture or video with a high resolution looks "better" than a picture or video with a low resolution.
However, we often forget some key aspects, namely the difference between physical resolution and optical resolution. These aspects together form a good image and form the basis for understanding upscaling. We'll also handle the pixel density – but do not worry – we'll keep things short and sweet.
- Physical resolution : On a TV datasheet, the physical resolution is simply called "resolution". "This is the number of pixels on a display. A 4K TV has more pixels than a 1080p TV, and a 4K picture is four times the size of a 1080p picture. All 4K displays contain the same number of pixels regardless of their size. Although high physical resolution televisions can use extra pixels to provide additional detail, this does not always work. The physical resolution is delivered to the optical resolution.
- Optical Resolution : That's why your old disposable camera images look better than the digital camera images of your discerning friend. If a photo looks sharp and has a clear dynamic range, it has a high optical resolution. Televisions sometimes waste their high physical resolution by displaying videos at a shitty optical resolution. This leads to blurred images and contrasts. Sometimes this is a result of upscaling, but we will come back to it soon afterwards.
- Pixel Density : The number of pixels per inch on a display. All 4K displays contain the same number of pixels, but for smaller 4K displays, the pixels are closer together so they have a high pixel density. For example, a 4K iPhone has a higher pixel density than a 70-inch 4K TV. We mention this to corroborate the idea that the screen size is not identical to the physical resolution and that the pixel density of a screen does not define the physical resolution.
Now that we've all eliminated the difference Between physical and optical resolution, it's time to start upscaling.
Upscaling makes a picture "bigger"
Each TV has a set of interpolation algorithms that scale up low-resolution images. These algorithms effectively add pixels to an image to increase resolution. But why should you have to increase the resolution of a picture?
The physical resolution is defined by the number of pixels on a display. This has nothing to do with the actual size of your TV. A 1080p TV screen only covers 2,073,600 pixels, while a 4K screen has 8,294,400 pixels. If you watch a 1080p video on a 4K TV without upscaling, the video will only take up a quarter of the screen.
For a 1080p image to fit on a 4K ad, the upscaling process requires 6 million pixels to be obtained (from that point it becomes a 4K image, but upscaling is based on a process called interpolation
Upscaling reduces the optical resolution.
There are several ways to interpolate an image, the most basic one being called the nearest neighbor interpolation. "To do this process, an algorithm adds Add a mesh of "blank" pixels to an image and then guess what color value each empty pixel should be by looking at its four neighboring pixels. The pixels will turn white, whereas an empty pixel surrounded by white and blue pixels will be light blue This is a straightforward process, but it leaves many digital artifacts, blurs and rough contours in one image In other words, interpolated images have poor optical resolution.
Compare these two images. The left is unprocessed, and the right is the victim of the next neighbor's interpolation process. The image on the right looks awful, though it has the same physical resolution as the image on the left. This happens to a small extent each time your 4K TV uses next-neighbor interpolation to scale an image.
"Wait a minute," you might say. "My new 4K TV does not look like that!" Well, that's because it's not based solely on nearest-neighbor interpolation – it uses a mix of image scaling techniques.
Scaling also tries to get the optical resolution under control
Okay, the interpolation of the next neighbor is faulty. This is a brute force method of increasing image resolution that does not take into account the optical resolution. For this reason, besides the interpolation to the nearest neighbor, televisions use two more types of interpolation. These are called bicubic (smoothing) interpolation and bilinear (sharpening) interpolation.
In bicubic interpolation (smoothing), each pixel added to an image is transferred to the 16 adjacent pixels to accept a color. This leads to a picture that is pronounced "soft". On the other hand, bilinear interpolation (sharpening) looks only at the next two neighbors and produces a "sharp" image. By mixing these methods and applying some filters for contrast and color, your TV can produce an image that has no noticeable loss of optical quality.
Of course, the interpolation is still a guessing game. Even with proper interpolation, some videos may show "ghosting" after scaling up, especially if your cheap TV does not like upscaling. These artifacts are also noticeable when enlarging very low quality (720p and lower) images to 4K resolution or images on incredibly large low pixel density televisions.
The picture above is not an example of the upscaling of a TV. Instead, this is an example of the upscaling of the HD DVD release Buffy The Vampire Slayer (taken from a video essay by Passion of The Nerd). It's a good (albeit extreme) example of how bad interpolation can ruin a picture. No, Nicholas Brendon does not wear waxy vampire makeup. That's exactly what happened to him during the upscaling process.
While all televisions offer upscaling, some may have better upscaling algorithms than others, resulting in a better picture.  Upscaling is necessary and rarely noticed
Despite all his mistakes, upscaling is a good thing. This is a process that usually runs smoothly and allows you to watch a variety of video formats on the same TV. Is it perfect Of course not. That's why some purists of movies and video games prefer to enjoy old art on their intended medium: old-fashioned televisions. From now on upscaling is no cause for excitement. There is no reason to be upset about that either.
It is worth noting that some of the hardware formats used daily already support 8K, 10K and 16K video formats. If upscaling technology can not keep up with these high-resolution formats, it can lead to a much higher quality loss than we are used to.
As manufacturers and streaming services are still on the rise 4K, but maybe we should not worry about 8K yet.