What is YUV?

[Graeme Nattress]

YUV is analogue component video in the process of being transformed into composite analogue video. Normally, you’ll never encounter this intermediary stage of video, but if you’re engineering a component to composite converter, you’ll have to know about it.

But…. when people say YUV, they often really mean YCbCr or YPbPr. YPbPr is analogue component video, and YCbCr is digital component video. People say YUV, but they really mean one of the above!

Y standa for luma – it is calculated as a weighted average of red, green and blue. Different weights are used for SD or HD video.

Cb and Cr are colour difference components that are scaled versions of red – luma and blue – luma. They store the “chroma” of the image. The component transform of RGB to YCbCr decorrelates the video signal, putting most of the information that’s useful to the eye and brain into luma, and puts leaving less detail in the chroma, making it much easier to compress. Often chroma is compressed by simply reducing it’s resolution in comparison to the luma – hence 4:2:2 where chroma is half the resolution of the luma.

Graeme

– http://www.nattress.com – Film Effects and Standards Conversion for FCP

[Seawild]

Wow! Thanks so much Graeme, good stuff to know.

[Graeme Nattress]

Thanks! If you really want a full technical description of this and other video terminology, my reference is Charles Poynton’s https://www.poynton.com/ HDTV book – it’s very technical and hard going, but it’s full of good info.

Graeme

– http://www.nattress.com – Film Effects and Standards Conversion for FCP