Human vision resolves brightness far more finely than colour, and almost every delivery codec exploits exactly that gap: it keeps full resolution for luma — brightness — while sampling colour at a fraction of the density, most commonly the near-universal 4:2:0, which keeps only a quarter of the colour samples a full-colour 4:4:4 image would carry at the identical pixel resolution.
That is easy to miss precisely because resolution and chroma subsampling are reported so differently — one is a pixel count everyone quotes, the other is a ratio almost nobody checks. A '4K' file is a 4:2:0 file the overwhelming majority of the time, which means its actual colour resolution sits far closer to a much smaller image than the headline number suggests.
Where it actually bites is colour-critical work: keying a subject off a background, or a fine colour grade, is where 4:2:0's coarser colour sampling shows up as ragged, stair-stepped edges around colour transitions that a sharper resolution setting does nothing to smooth. It is exactly why a working master is worth keeping at 4:2:2 or 4:4:4 even when every public delivery copy is going to be downsampled to 4:2:0 regardless.
In practice
- Do not read '4K' as a claim about colour detail — resolution and chroma subsampling are separate specs, and delivery formats routinely maximise the first while minimising the second.
- Keying or fine colour work wants 4:2:2 or 4:4:4 if the option exists; 4:2:0 is where keyed edges turn ragged first.
- Every mainstream social platform re-encodes to 4:2:0 on ingest regardless of what was uploaded, so this mostly matters for a working master, not the final public copy.
The mistake to avoid
Assuming a high-resolution export is automatically high in every kind of detail. Chroma subsampling is decided independently of pixel count, and the near-universal 4:2:0 default quietly caps colour precision on files that are otherwise pin-sharp.
Go deeper
Pick a Mezzanine Codec You Can Reopen
Platform MP4s are not masters. Compare ProRes 422 HQ, DNxHR HQX, and FFV1 for 10-bit 4:2:2, alpha, audio tracks, and a file you can still open in five years.
Related terms
Codec
A codec is the scheme that compresses video or audio down to a storable size, and it is a different thing from a container format like MP4 or MOV, which is only the wrapper the codec's data travels inside.
Resolution
Resolution is how many pixels an output contains, usually named by its height — 720p, 1080p, 4K — and set before generation rather than after.
Background removal
Background removal separates a subject from everything behind it and discards the rest, leaving a cutout you can place on any backdrop.
Upscaling
Upscaling raises the resolution of media you already have, inventing plausible detail rather than recovering detail that was never recorded.
Hook rate
Hook rate is the share of people shown a video who are still watching a few seconds in — the number that grades the opening, not the edit behind it.
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