In screen resolution, the rule of thumb used to be “more pixels is better.” Is the technology starting to reach a limit?

While 8K technology is currently being presented at industry trade shows and conferences, the jump in pixels may not be an improvement over 4K for applications in television and movies, according to advanced imaging engineer and cinematographer Pierre Routhier.

4K and 8K resolution refer to the number of pixels in the horizontal display of a screen. For a movie screen, 4K is 4,096 pixels wide and 8K is 8,192 pixels wide. The spatial resolution of 4K, or number of pixels in the display, is four times the resolution of high-definition displays, while 8K is roughly double the resolution of 4K. Does this make 8K twice as good?

Not necessarily, according to Routhier. 8K allows for much more detail in static shots, but the extra detail can have a zero, or even a negative effect on shots with a lot of action and certain close-ups.

In movies and television, a basic element of filmmaking is shot framing. Shots in a scene can vary from extremely close to extremely far away.

Figure 1: Shot framing in motion pictures

To emphasize emotion, close-ups usually contain little or very subtle motion. Similarly, wide shots, used to convey a sense of location, focus more on settings and landscapes and don’t typically have a lot of movement. Action shots, on the other hand, contain a lot of motion, from the protagonists or camera.

In cinematic action shots, Routhier’s models on resolution and camera speed demonstrate frame rate technology has to be significantly improved to make 8K technology practical.

“The main factor here is motion. At classic frame rates like 24 frames per second (fps), the blur due to motion is too high to achieve detail due to the low frame rate,” said Routhier. “Increasing spatial resolution just means blur will be covered by more pixels – the image will not be clearer to the viewer. Our studies show below incredibly high frame rates – like 240 fps, which is 10 times the standard fps – most of the shots in a movie or a TV show will be blurry and not benefit much from 8K.”

Besides motion blur, the extreme detail in close-ups can also be an issue. 8K can make certain features of an actor or actress – such as blemishes or wrinkles – unflattering. As a result, image softening is often required, which reduces resolution.

In addition to examining the difficulties of framing certain shots in 8K, Routhier also analyzed the technology in different real-world scenarios to determine the minimum viewing conditions where a viewer can perceive 8K. His scenarios looked at household television, the standard movie theater and IMAX-sized screens.

“To see the difference between 4K and 8K (if we had non-blurry images) with the standard 20/20 human vision, we would need such huge screens that they would not fit in our living rooms,” said Routhier. “In theaters, we would have to be so close to the screen that we could not see the entire image. The only venue that would benefit would be the large IMAX-type screen.”

Going forward, Routhier is looking to show how the use of higher frame rates, such as 120 fps in HD and 4K, would provide a better experience for viewers as opposed to increasing spatial resolution to 8K.

He is also looking to develop books and host educational sessions that help content creators, broadcasters and studios better understand screen resolution technology and the work that needs to be done to truly evolve the viewer experience.

Routhier’s research was presented during the 2017 Society of Motion Picture and Television Engineers (SMPTE) Annual Technical Conference and Exhibition in Hollywood, CA. To access more content from SMPTE, visit the IEEE Xplore Digital Library.