Hacker News Reader

Comment by rix0r | Hacker News Reader

> This is how DVDs work: a high res green image and two low-res images, one for red, one for blue.

Not true. MPEG-2 uses the YCbCr colorspace, consisting of a high resolution Luminance signal (brightness) and a low resolution Chrominance signal (color). So in fact, all color information is subsampled, green is not treated specially.

View on HN

Green is absolutely treated specially in YCbCr; you just have to understand how YCbCr relates to RGB.

ITU-R BT.601 defines YCbCr as follows:

    Y ~= 0.30 R + 0.59 G + 0.11 B
    Cb ~= -0.17 R - 0.33 G + 0.5 B
    Cr ~= 0.5 R - 0.42 G - 0.08 B

Y is given the most bandwidth, and green makes up 60% of Y. Cb and Cr are allocated substantially less bandwidth, and green still makes up a sizable chunk of the value. In total, green occupies about 2/3 of the bandwidth in YCbCr. That's pretty much the whole point of doing it---RGB spends an unnecessary amount of bandwidth on R and B.

(reference: http://en.wikipedia.org/wiki/YCbCr )

Indeed. The author of this article is pretty badly misinformed.

Reply on news.ycombinator.com