Chroma Subsampling 4:2:0 vs 4:4:4
Also known as: 420 vs 444, chroma subsampling photos, chroma subsampling 420, 4:2:0 vs 4:4:4
Chroma subsampling stores full brightness (luma) but fewer color (chroma) samples to shrink files. **4:4:4** keeps every color sample; **4:2:0** keeps a quarter of them, roughly halving raw data with little visible loss because eyes are far less sensitive to color detail than brightness.
- 4:2:0 keeps one color sample per 2x2 pixel block; 4:4:4 keeps color for every pixel.
- Switching from 4:4:4 to 4:2:0 discards roughly half the color data with little visible loss.
- JPEG, HEIC, H.264, and HEVC phone capture default to 4:2:0; 4:4:4 is used for text and graphics.
How 4:2:0 and 4:4:4 differ
The notation describes a 4-pixel-wide reference block: the first number is luma resolution, the next two are how many chroma (color) samples are kept on the top and bottom rows. 4:4:4 keeps color for every pixel. 4:2:2 keeps color for every other pixel horizontally. 4:2:0 keeps one color sample per 2x2 block of pixels, so color is stored at a quarter resolution.
Because human vision resolves brightness much more sharply than color, throwing away most chroma data is nearly invisible in normal photos and video. That is why 4:2:0 is the default for JPEG, HEIC, H.264, and HEVC capture on phones, while 4:4:4 is reserved for screen recordings, text, graphics, and professional color work where sharp color edges matter.
Why it shrinks file size
Subsampling reduces the raw data before the codec even starts compressing. Moving from 4:4:4 to 4:2:0 discards about half of the color information, which the encoder no longer has to store or compress. On top of that, smoother low-resolution chroma channels compress more efficiently, so real-world savings often exceed the raw 50% reduction.
The trade-off shows up only on hard color edges: thin colored text, fine line art, or saturated red-on-black detail can look slightly blurred or show color fringing in 4:2:0. For camera-roll photos and recorded video this is essentially undetectable, which is why phone cameras and the duplicate and large-file scans in a cleaner like Cleanor almost always deal with 4:2:0 media.