How does converting a video to 4K actually work?
Converting older video footage to 4K is increasingly tempting as 4K OLED displays become standard, but the process involves significant technical limitations that anyone attempting it should understand. Upscaling software cannot recover detail that was never captured in the original recording; instead, it uses interpolation to estimate and generate the additional pixels needed, which can leave footage looking softer, smoother or unnaturally processed if sharpening and noise reduction are not carefully balanced.
Moving from 1080p to 4K requires four times as many pixels overall, and the quality of the result depends heavily on the original source material rather than the conversion process itself. The article cites the HD restoration of Star Trek: The Next Generation as an example of doing this well: CBS commissioned the 2011 project using the show's original 35mm film negatives, equivalent to roughly 20 megapixels of detail, across 25,000 reels of film stock. The remaster of all seven seasons took over three years and reportedly cost more than $12 million (USD), but succeeded because the source material contained far more detail than the original broadcasts. By contrast, converting content whose best available source is already low-resolution offers no such advantage, since all the "extra" pixels must be guessed.
- Converting video to 4K can't recreate detail that was never recorded.
- Upscaling relies on software estimating extra pixels, often softening footage.
- Star Trek: TNG's HD remaster used original film negatives, cost over $12m.
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4K video has four times as many pixels as 1080p, so older footage needs to be enlarged to fill a 4K screen. Software estimates the extra pixels from those already in the image; it cannot restore detail that the camera or film never captured.
The result depends largely on the best source available. A high-quality film negative may hold much more detail than an old television broadcast, while low-resolution footage gives the software less information to work with.
Restoring Star Trek: The Next Generation for HD showed what a richer source can make possible: the work used the original 35mm film negatives, rather than simply enlarging the broadcasts. Such restorations can take years and cost millions, and sharpening or noise reduction can affect how natural the converted image looks.