2026-09-20
Have you ever exported two images at the same dimensions and the same quality setting, only to find one looks noticeably muddier than the other? The culprit is often not the quality slider at all, but chroma subsampling — a parameter almost nobody checks.
Digital images store brightness (luma) and color (chroma) separately. The human eye is extremely sensitive to brightness but surprisingly forgiving about color detail: blur the color slightly and we barely notice. Chroma subsampling exploits exactly that. Full luma detail is kept, while color is sampled less densely, which saves a large amount of data.
This is why the same photo can shift in color edges after you export it at maximum quality from Photoshop and then run it through an online tool once more: the two exports chose different subsampling modes.
If the image is photographic and the goal is page speed, 4:2:0 is the best default by a wide margin: dramatically smaller files with no visible difference at normal viewing distance. Only when the picture contains lots of sharp colored edges (text, logos, line art, saturated blocks) should you step up to 4:4:4 or switch to PNG outright.
Yes, significantly. Dropping from 4:4:4 to 4:2:0 leaves a quarter of the color data, which typically cuts total size by 10 to 25 percent on photographic images.
Rarely at normal size on photos. But zoom into sharp colored edges, such as red text on white or a thin-line chart, and 4:2:0 shows clear color fringing or smearing.
No. It is lossy, and discarded color information cannot be recovered. If you plan repeated edits, keep a 4:4:4 or lossless master.