HDR vs. 4K: What's the Difference?

4K and HDR both improve image quality, but not in the same way.

When shopping for a TV you may come across the terms "4K" and "HDR." Both of these technologies help improve image quality—but they do so in very different ways. Let's cut through the noise and learn what they mean.

HDR vs 4K

Overall Findings

4K
  • Refers to screen resolution—the number of pixels a screen can fit.

  • Used synonymously with "Ultra HD" (UHD). Refers to horizontal screen resolution of roughly 4,000 pixels.

  • 4K/UHD TV standard is 3840 x 2160 pixels. 4K cinema standard is 4096 x 2160 pixels.

  • Four times the number of pixels as 1080p, which means four 1080p images can fit in the space of one 4K resolution image.

  • Requires UHD-compatible devices and components to avoid upscaling

HDR
  • Stands for "High Dynamic Range."

  • Wider color gamut and contrast range than Standard Dynamic Range (SDR).

  • Bright tones made brighter without overexposing. Dark tones made darker without underexposing.

  • Greater visual impact than 4K: More accurate colors, smoother light and color shading, more detailed images.

  • Resolution-agnostic: Does not change screen resolution.

What is 4K?

4K refers to screen resolution, which is stated in pixels. For digital televisions, 4K can mean one of two resolutions. The most common is the "Ultra HD" or "UHD" format of 3,840 horizontal pixels by 2160 vertical pixels. The less common resolution, mostly reserved for cinema and movie projectors, is 4096 × 2160 pixels.

Each 4K resolution is 4 times the number of pixels (or twice the lines) as a 1080p display—the next highest resolution you'll find in a consumer television. That means you can fit four 1080p images in the space of one 4K resolution image.

With an aspect ratio of 16:9, or "16 by 9," the total number of pixels in a 4K image exceeds 8 megapixels.

4K (as well as every other TV resolution) remains constant regardless of screen size. However, the number of pixels per inch can vary depending on the size of the screen. This means as TVs screen grow in size, pixels are increased in size or spaced farther apart to achieve the same resolution.

4K resolution may also be referred to as Ultra HD, UHD, 2160p, Ultra High Definition, or 4K Ultra High Definition.

What You Need To Know When Shopping for a 4K TV

What is HDR?

HDR stands for High Dynamic Range, which is different than resolution. The dynamic range refers to the contrast or range between the lightest and darkest tones in an image. HDR delivers a higher contrast—or larger range—than Standard Dynamic Range (SDR).

As a technology, HDR expands the distance between white and black, making the contrast more intense without overexposing bright colors or underexposing dark colors.

When high dynamic range images captured, the information is used in post-production to "grade" the content so that the widest possible contrast range is obtained. The images are graded to produce a wide color gamut, which makes for deeper, more saturated colors, as well as smoother shading, and more detailed images. Grading may be applied to each frame or scene, or as static reference points for an entire film or program.

How HDR Should Look On Your TV Screen

When an HDR television detects HDR-encoded content, bright whites will appear without blooming or washout, and deep blacks without muddiness or crushing. In a word, the colors will look more saturated.

For example, in a sunset scene, you should see the bright light of the sun and the darker portions of the image with similar clarity, along with all the brightness levels in between.

There are two ways for a TV to display HDR:

  • HDR Encoded Content: There are four primary HDR formats: HDR10/10+, Dolby Vision, HLG, and Technicolor HDR. The brand or model of HDR TV determines which format it is compatible with. If a TV can't detect a compatible HDR format, it will display the images in SDR.
  • SDR to HDR processing: Similar to how TVs can upscale resolutions, HDR TV with SDR-to-HDR upscaling can analyze the contrast and brightness information of an SDR signal and expand the dynamic range to approximate HDR quality.

Not All TVs With HDR Are Created Equal

How well an HDR-enabled TV displays HDR depends on how much light the TV can emit. This is referred to as Peak Brightness and is measured in Nits.

Content encoded in the Dolby Vision HDR format, for example, may provide a range of 4,000 nits between the blackest black and the whitest white. Few HDR TVs can emit that much light, but a growing number of displays can reach 1,000 nits. Most HDR TVs will display less. OLED HDR TVs max out between 750 and 800 nits, while low-end LED/LCD HDR TVs may emit just 500 nits. However, because the pixels in an OLED TV are individually lit they can display absolute black, and thus have a higher perceived dynamic range.

When a TV detects an HDR signal but can't emit enough light to display its full dynamic potential, it will employ Tone Mapping to best match the dynamic range of the HDR content with that of TV's light output.

What You Need To Know When Shopping for an HDR TV

  • HDR is resolution-agnostic. That means HDR encoding does not affect a given display's resolution. HDR is implemented on top of 4K, not in place of it.
  • The visual difference between SDR and HDR can be seen on any screen size. However, the HDR effect may look different from TV to TV depending on the amount of light the display can emit.
  • Not all HDR TVs feature SDR-to-HDR processing.
  • When shopping for a TV with HDR capability, consider the TV's compatibility with HDR10/10+, Dolby Vision, and HLG formats, as well as the TV's peak brightness capability, which is measured in nits.

4K vs HDR – The Bottom Line

Whether shopping for a standard 4K TV or a 4K TV with HDR, keep the following in mind.

  • Pixels are the foundation from which 4K resolution is established and HDR is one way to make pixels look their best.
  • HDR has a bigger visual impact than 4K.
  • Since 4K TVs are the majority of TVs available and sold, content creators and distributors, along with TV makers have prioritized the application of HDR to 4K Ultra HD TVs over 1080p or 720p TVs (with limited exceptions noted below).
  • In the U.S. almost all HDR TVs are 4K TVs, but not all 4K TVs are HDR TVs.
  • For best viewing results, consider a TV that incorporates both 4K and HDR.
  • If you are considering the purchase of an 8K TV, HDR is an included standard feature.

There is a small select number of LG 1080p FHD (LK and LM5700 Series) and 720p HD (LK540, 610, 620 Series) TVs that include HDR compatibility. Also, in Europe, Sony offers a select number of 1080p TV models (WF66, RF45, WE75, WE66, WE61, RE45). These sets are compatible with 1080p HDR gaming and streaming content (such as from Netflix) that may include HDR encoding.