We’ve established that 4K displays have more pixels. We’ve shown how those pixels will be better because they can show more colors. Now we’re going to talk about brightness and contrast. These are important components of up and coming 4K UHD technology.
Brighter is Better
The first thing to understand is the importance of brightness. Screen brightness is measured in nits. Obviously, screens have to be bright enough to overcome background light. But brightness is important for another reason, too. A screen’s brightness determines the total available contrast of the screen. Black is the screen’s darkest, and pure white is its brightest. If the white value is higher (brighter), there are more shades between the black and white. With more levels available, more contrast can be shown.
So what do these nit numbers mean? If you’re reading this on your Google Nexus 6, you’re looking at a 270 nit display. That’s about the same brightness you’ll find on a MacBook Air, and the iPhone 6 has closer to 500 nits of brightness. Generally, TVs are dimmer. Depending on the type, 100-400 nits is standard.
The question for 4K developers remains: how bright should TVs be? Well, eyestrain becomes an issue around 850 nits. But that’s only a problem if you’re staring at a solid white screen. When Dolby tested normal viewing, they found that people preferred displays around 20,000 nits! The most notable benefit of such bright displays is that they have a huge range of contrast. Light areas of the screen and dark areas can both contain many shades of detail, leading to a much more realistic image.
High Dynamic Range Matters
Having many possible shades makes a huge impact on picture quality. With increased detail across all areas of the screen, bright, high-contrast displays look real. This is especially true when bright displays are paired with High Dynamic Range (HDR).
HDR is a film processing technique that combines different exposure levels. Dark areas of the scene can use low exposure and bright areas rely on high exposure. This prevents details from being washed out or lost in shadow, as would happen with traditional processing.
Here’s an example:
This HDR photo shows detail in the bright cathedral windows, like a traditional low exposure shot. But it simultaneously shows detail in the dark rafters, which would be completely black in low exposure. Conversely, if the exposure were set to capture detail in dark areas, the windows would be washed out. HDR corrects both of those problems by blending separate shots using different levels of exposure. The 6 photos used to create the single HDR image above show how each exposure level captures different details:
With HDR image processing and bright displays, screen images will look incredibly lifelike. In fact, these changes will make a more visible difference than a simple change in resolution. When consumers buy 4K, what they’ll really be buying is this enhanced image package. Expect these technologies to be an essential part of next-generation 4K UHD displays.