What is 4:2:0 Chroma Subsampling? (The Hidden Quality Killer)
DefinitionA compression trick that lowers color resolution while keeping brightness.
1The Simple Explanation
Your eyes are more sensitive to brightness (Luma) than color (Chroma). Engineers save space by storing a black-and-white image at full quality, but the color map at half or quarter resolution. This is Subsampling.
2Technical Deep Dive
Notation like 4:4:4 means no subsampling (perfect quality). 4:2:0 means color resolution is quartered. This is standard in JPEG and video (HEVC). It ruins sharp red text on dark backgrounds.
Common Misconceptions
Myth: High quality JPG means no subsampling. Fact: Even 100% quality JPGs often use 4:2:0 subsampling depending on the save settings. Use PNG for text.