> 1) Throw away fine detail by discarding high frequency components The reason it works is that fine detail is almost completely correlated across colors, so i

> 1) Throw away fine detail by discarding high frequency components The reason it works is that fine detail is almost completely correlated across colors, so if you only keep the Y plane at full resolution it still stores it. You couldn't just throw it out in RGB space because eg text would be unreadable.