NTSC Colors and HD

[Guiboche]

Maybe this is a question edDV can answer.

Do the same rules of "NTSC Colors" that apply to standard D1 content apply to HD content as well?

Since, it is my understanding that HD uses the same rules as SD does for NTSC. If anything, HD has better support for superwhite and superblack (the 235-255 and 0-16 range).

If HD is the same color space as SD, then the talk of HD having "More Colors" isn't even true.

Can anyone elaborate as to the rules and specs of the HD Color space?

[JohnnyMalaria]

Colorspace and the 16-235 thing are separate issues.

Video formats use colorspaces based upon Y (luma - the black and white) and C (chroma - the color information) - aka Y/C. Chroma is split into two - Cr and Cb. So, the colorspaces used are of the YCrCb family. Often, these are erroneously labelled YUV. But that's a technicality which I'll skip.

Of course, the video camera and TV used to capture and display the video work in the world of Red, Green and Blue - RGB colorspaces.

Somewhere, the RGB has to be converted to Y/C and back again. (One of the reasons for the use of the Y/C is so that TV signals are backwards compatible with black and white TV. A black and white TV does 'see' the C, just the Y.)

In an ideal world, every Red, Green and Blue part of the image would be recorded/transmitted/displayed but that's very costly in terms of bandwidth and requires electronics that can work at high frequencies (less a problem today than 30 years ago).

The clever bit - human vision perceives detail in the brightness and contrast of a scene - the black and white part. Color doesn't really add to the detail. So, keep the black and white part at high detail (the Y) and throw away some of the color. We can't really tell with our eyes.

In standard definition MPEG2 (DVD), for every 2x2 pixel block of black and white information, only 1 pixel of color information is kept. This is termed 4:2:0 (a rather odd terminology that merits a discussion all of its own). The ideal is that every 2x2 pixel block of black and white would have a corresponding 2x2 pixel block of color - this is 4:4:4.

High definition strikes a balance between the two - namely 4:2:2.

Furthermore, some HD formats use 10-bit precision for the signals (0 - 1023 instead of 0 - 255).

So....yes, HD can have more colors since you can have 1024 values per pixel value instead of 256 and HD can have more color detail.

[edDV]

Maybe this is a question edDV can answer.

Do the same rules of "NTSC Colors" that apply to standard D1 content apply to HD content as well?

Since, it is my understanding that HD uses the same rules as SD does for NTSC. If anything, HD has better support for superwhite and superblack (the 235-255 and 0-16 range).

If HD is the same color space as SD, then the talk of HD having "More Colors" isn't even true.

Can anyone elaborate as to the rules and specs of the HD Color space?

Simple answer is Rec BT.601 (standard def) and Rec BT.709-4 (high def) obey similar rules for 8 and 10 bit luminance levels but colorimetry details have slight differences.

The practical problems are mostly related downconverting HD (wide color space) to SD (narrower) or to NTSC/PAL (much narrower).

This paper supplies additional detail.
http://www.broadcast.harris.com/videotek/whitepapers/ConformingSD-RGB.pdf

[Guiboche]

Thanks!