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

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

Overall Findings

4K and HDR are not competing standards. 4K refers to screen resolution (the number of pixels that fit on a television screen or display). It's sometimes referred to as UHD or Ultra HD, although there is a slight difference.

HDR stands for High Dynamic Range and refers to the contrast or color range between the lightest and darkest tones in an image. HDR delivers a higher contrast—or larger color and brightness range—than Standard Dynamic Range (SDR), and is more visually impactful than 4K. That said, 4K delivers a sharper, more defined image.

Both standards are increasingly common among premium digital televisions, and both deliver stellar image quality. TV makers prioritize the application of HDR to 4K Ultra HD TVs over 1080p or 720p TVs. There is little need to choose between the two standards.

Resolution: 4K Is the Standard

4K refers to a specific screen resolution, and HDR has nothing to do with resolution. While HDR has competing standards, some of which specify a minimum 4K resolution, the term generally describes any video or display with a higher contrast or dynamic range than SDR content.

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 four 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 that four 1080p images fit 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 eight megapixels.

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

HDR televisions must meet a set of brightness, contrast, and color standards to be considered HDR. Those standards vary, but all HDR displays are defined as having a higher dynamic range than SDR, as well as minimum 10-bit color depth. As most HDR TV are 4K TVs, most have a resolution of 3840 x 2160 pixels (there are a small number of 1080p and 720p HDR TVs).

Some LED/LCD HDR TVs have a peak brightness output of 1,000 nits or more. For an OLED TV to qualify as an HDR TV, it must output at least 540 nits of peak brightness. Most top out at about 800 nits.

Color and Contrast: HDR Is Visually Impactful

Color reproduction improves dramatically in HDR televisions. As a resolution, 4K does not affect color all that much, other than providing added definition. This is why 4K and UHD often go hand in hand. These technologies complement the two most important aspects of picture quality—definition and color.

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

When high dynamic range images are captured, the information is used in post-production to grade the content and obtain the widest possible contrast range. 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.

When an HDR television detects HDR-encoded content, bright whites appear without blooming or washout, and deep blacks without muddiness or crushing. In a word, the colors 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. Check out the example below.

There are two ways for a TV to display HDR:

• HDR Encoded Content: The four primary HDR formats are 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 displays the images in SDR.
• SDR to HDR processing: Similar to how TVs upscale resolutions, HDR TV with SDR-to-HDR upscaling analyzes the contrast and brightness information of an SDR signal. Then, it expands the dynamic range to approximate HDR quality.

Compatibility: End-to-End for the Full 4K HDR Experience

4K televisions require end-to-end compatibility among all components to produce authentic or true 4K resolution. The same is generally true of HDR. You need both an HDR TV and content that was produced using an HDR format. By some measures, there is less content available in HDR than there is in 4K, but that's beginning to change.

To enjoy full 4K UHD resolution, you need 4K-compatible equipment down the line. That includes home theater receivers, media streamers, Ultra HD Blu-ray players, and 4K video projectors, as well as the original resolution of the content you're watching. You'll also need a high-speed HDMI cable. 4K is more common among larger televisions because the difference between 4K and 1080p is not as noticeable on screens smaller than 55 inches. However, the HDR effect may look different from TV to TV, depending on the amount of light the display emits.

Some 4K devices upscale lower resolutions to 4K, but the conversion isn't always smooth. 4K hasn't been implemented in over-the-air TV broadcasting in the U.S., so over-the-air (OTA) content will need to be upscaled to view in 4K. Similarly, not all HDR TVs can upscale from SDR to HDR. 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.

How well an HDR-enabled TV displays HDR depends on how much light the TV emits. 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 emit that much light, but a growing number of displays reach 1,000 nits. Most HDR TVs display less.

OLED TVs max out at about 800 nits. A growing number of LED/LCD TVs emit 1,000 nits or more, but lower-end sets may emit only 500 nits (or lower). On the other hand, since the pixels in an OLED TV are individually lit, enabling the pixels to display absolute black, these TVs may have a higher perceived dynamic range even with lower peak brightness levels.

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

4K vs. HDR: Do You Have to Choose?

4K and HDR are not competing standards, so you don't need to choose between the two. And because most premium TVs have both standards, you don't need to focus on one standard over the other, especially if you're buying a TV that's larger than 55 inches. If you want a smaller TV than that, you may be happy with a 1080p display, as you probably won't notice the difference in resolution.

Frequently Asked Questions

• Is HDR better than 4K? Which you'll appreciate more depends on who you are and your personal setup. HDR works in the context of contrast and colors and brightness, while 4K refers to resolution, which is the number of pixels in an image.
• Is HDR better than HD? One is not better than the other, as HD and HDR are totally separate concepts. HD refers to resolution like 4K does, while HDR works in the context of contrast, colors, and brightness.
• Is HDR different on phones, cameras, and displays? No, HDR is HDR, though you'll use an HDR camera to create HDR content and use an HDR display to view HDR content. What you can do with HDR will vary based on device, but the technology doesn't change.
• Should I use HDR? It's down to preference. If you have an HDR camera or a phone, chances are you'll want to use it. In a TV or monitor, how good the HDR implementation itself is will likely determine whether you'll want to use it or not.