Resolution is a count of pixels
A screen picture is built from a grid of tiny dots called pixels. Video resolution is the size of that grid, written as width by height. More pixels allow finer detail, at least in principle.
The common names are:
| Name | Pixel grid | Approximate pixels |
|---|---|---|
| HD (720p) | 1280 x 720 | 0.9 million |
| Full HD (1080p) | 1920 x 1080 | 2.1 million |
| 4K (Ultra HD, 2160p) | 3840 x 2160 | 8.3 million |
The number in 1080p or 2160p refers to the vertical line count. The p stands for progressive scan, meaning each frame is drawn whole. Marketing names such as 4K are loose; television 4K is 3840 x 2160, which is slightly narrower than the 4096-wide format used in cinema.
Doubling the width and height quadruples the pixels. Going from 1080p to 4K therefore means four times as many, since 1920 x 2 is 3840 and 1080 x 2 is 2160. That is a large jump in data, which is why 4K streams require more bandwidth.
What a screen needs
To show a given resolution, the screen must actually have that many pixels. A 1080p television can accept a 4K signal on many models, but it will scale it down to fit. You gain nothing from the extra detail, although the picture may still look fine.
Other requirements for 4K include:
- A source that provides 4K. The streaming plan, the app, the title and the device all need to support it. Some services reserve 4K for a higher-priced plan.
- A device that can decode it. Streaming sticks, consoles and smart TVs must support the codec used for 4K video. The processing involved is covered in the explanations of the central processing unit and graphics card, which handle decoding in many devices.
- A suitable connection. HDMI cables and ports need to support the data rate, and older cables or ports may not carry 4K with HDR at higher frame rates. If a picture flickers or HDR switches off, a cable or port setting is a frequent cause.
- Enough bandwidth. Streaming 4K typically needs a noticeably faster connection than HD. Services often publish a recommended speed, commonly somewhere in the region of 15 to 25 megabits per second, but check your own service’s guidance. A speed test and a look at your Wi-Fi speed show whether your connection is likely to keep up.
Does more resolution always look better?
Not necessarily. Whether you can see the extra detail depends on screen size and how far you sit. On a small screen viewed from across a room, the eye cannot pick out individual pixels, so 4K and 1080p can look similar. On a large television viewed from a normal distance, 4K is more likely to look sharper. Individual eyesight matters too.
Source quality is just as important. A title that was filmed or mastered in high quality looks better than an upscaled older one. Upscaling stretches a lower resolution to fill the screen, and modern televisions do this fairly well, but it cannot add real detail that was never captured. Heavy compression also softens the picture, and a high-resolution label on a heavily compressed stream does not guarantee crispness.
On a phone, screen sharpness is described with other terms, and the article on how phone screens work, including refresh rate, covers that side.
What HDR adds
HDR stands for high dynamic range. Resolution is about how many pixels there are; HDR is about what each pixel can show. It widens the range between the darkest and brightest parts of a picture, and usually the range of colours too.
In a standard picture, a sunlit window and a shadowy corner are squeezed into a limited brightness range, so details at the extremes may be lost. With HDR, bright highlights can be brighter and dark areas can keep more shading, which can make a scene look more natural and punchy.
Several HDR formats exist. HDR10 is a widely supported baseline. Dolby Vision and HDR10+ add information that adjusts the picture scene by scene. HLG is designed mainly for broadcast. A television may support some formats and not others, and content is delivered in whichever format its source provides.
HDR depends on the display
The benefit of HDR depends heavily on the screen. A television that can reach high brightness and produce deep blacks shows HDR well. A budget model may accept an HDR signal but lack the brightness to make much of it, and the result can look dim or washed out compared with standard video. The label HDR on a box does not guarantee a strong result, so it is worth checking reviews and, where possible, seeing the screen in person.
Room lighting matters as well. HDR is often at its best in a dim room, where contrast is easier to see.
Many people find HDR a more noticeable improvement than the jump from 1080p to 4K, though opinions differ and it depends on the screen and the material.
Frame rate and other labels
Two other terms often appear. Frame rate is how many pictures are shown per second, such as 24, 30 or 60. Films are commonly 24 frames per second; sport and games often use 60 or more. Bit depth affects how smoothly colours blend. Neither is the same as resolution, so a stream can be 4K and still look different from another 4K stream.
Choosing sensibly
- Check what your screen supports, and which HDR formats.
- Check that your streaming plan and device offer the quality you want.
- Use a cable and port rated for the signal.
- Make sure your connection is steady, not just fast on a test.
- Do not pay extra for resolution you will not see from your seat.
When picture quality drops or a stream stalls, the cause is often the connection and not the screen, which is covered in why video buffers.