As 4K replaces HD in our homes, manufacturers are unveiling some interesting marketing jargon, like “Ultra HD upscaling” (UHD). But upscaling isn’t some unique feature—it just allows 4K TVs to work with lower resolution video formats, like 1080p and 720p.
All TVs Have Upscaling
Upscaling means low-resolution content will fill your entire TV screen. Without it, a low-resolution video takes up less than half of the screen space. This is a typical feature on all TVs. Even 1080p TVs had it—they could upscale 720p content and display it in full-screen mode on a 1080p screen.
UHD upscaling is what makes your 4K TV work like any other. It can take lower-resolution content and display it on the entire 4K screen.
Upscaled 1080p content on a 4K screen often looks better than 1080p content on a normal 1080p screen. But upscaling isn’t magic—you won’t get the sharp image you would from true, native 4K content. Here’s how it works.
Resolution Exists at a Physical and Visual Level
Before getting into upscaling, we need to understand the concept of image resolution. At a glance, it’s a relatively simple concept. An image or video with a high resolution looks “better” than an image or video with a low resolution.
However, we tend to forget some key aspects, namely, the difference between physical resolution and optical resolution. These aspects work together to create a good image, and they’re the basis for understanding upscaling. We’re also going to cover pixel density—but don’t worry—we’ll keep things short and sweet.
- Physical Resolution: On a TV spec sheet, the physical resolution is simply referred to as “resolution.” It’s the number of pixels on a display. A 4K TV has more pixels than a 1080p TV, and a 4K image is four times the size of a 1080p image. All 4K displays, regardless of their size, contain the same number of pixels. While TVs with a high physical resolution can use their extra pixels to offer additional detail, it doesn’t always work out that way. Physical resolution is at the mercy of optical resolution.
- Optical Resolution: This is why your old disposable camera photos look better than your pretentious friend’s fancy digital camera photos. When a photo looks sharp and has a clear dynamic range, it has a high optical resolution. TVs sometimes squander their high physical resolution by displaying video with a crappy optical resolution. This leads to blurry images and contrast. Sometimes, this is a result of upscaling, but we’ll get back to that in a minute.
- Pixel Density: The number of pixels per inch on a display. All 4K displays contain the same amount of pixels, but on smaller 4K displays, the pixels are closer to each other, so they have a high pixel density. A 4K iPhone, for example, has a higher pixel density than a 70-inch 4K TV. We’re mentioning this to reinforce the idea that screen size isn’t the same thing as physical resolution, and that a screen’s pixel density doesn’t define its physical resolution.
Now that we’re all brushed up on the difference between physical and optical resolution, it’s time to get into upscaling.
Upscaling Makes an Image “Bigger”
Every TV contains a mess of interpolation algorithms, which are used to upscale low-resolution images. These algorithms effectively add pixels to an image to increase their resolution. But why would you need to increase an image’s resolution?
Remember, physical resolution is defined by the number of pixels on a display. It has nothing to do with the actual size of your TV. A 1080p TV screen is comprised of only 2,073,600 pixels, while a 4K screen has 8,294,400. If you show a 1080p video on a 4K TV without upscaling, the video will take up only a quarter of the screen.
