Legal color? at DVinfo.net

Warren Kawamoto · October 23rd, 2007, 02:52 PM

The in "look" now is crushed blacks, oversaturated color, blown out highlights. These shots look really cool on computer screens and monitors. The problem is that we need to broadcast some of these shots on tv. Currently, our crushed blacks are at -10 IRE, and chroma and highlights are way over 120%, which is not broadcast legal. My question is: How can we maintain this "look" on broacast television and still be legal?

Vito DeFilippo · October 24th, 2007, 08:31 PM

Crushed blacks and blown highlights don't have to be outside legal limits. Some NLE's have effects that will make your levels legal, or in the colour correction tools will let you clip luminance above and below legal limits.

I routinely clip above and below legal limits while I do my colour correction, though I could be much more anal about it than I am.

The problem with using a legaliser effect on the whole timeline is that you then have to render the entire thing...

Warren Kawamoto · October 24th, 2007, 10:20 PM

Vito,
Thanks for your reply. I can see "compressing" the crushed blacks and highlights to keep them within legal limits, but what about chroma? There is no way to de-saturate over-saturated color without losing the look. Or is there?

Vito DeFilippo · October 25th, 2007, 07:17 AM

It's not a matter of 'compressing' the luminance. It's a matter of clipping outside values. The distribution of luminance values within the extremes stays the same, so the look stays pretty much the same.

I'm a bit fuzzier on whether the same is true of chroma, so I won't speculate. Perhaps someone with more broadcast experience will chime in on that one.

Vito DeFilippo · October 25th, 2007, 07:28 PM

Warren,

This is from the AVID help menu, if it's interesting:

"Safe Color Limits with Waveform and Vectorscope Information
To stay well within the limits of television transmitters, cable systems, satellite links, DVD encoders, and so on, broadcasters or distributors often issue safe color limits for video levels. Video levels outside safe color limits are generally known as "illegal." Of course, no law is broken if you exceed the specified limits, but the program might be rejected on technical grounds or the image quality might suffer with further processing. If you know that your delivery master is a VHS tape that does not handle high chroma well, set some reasonable limits by yourself.
In Y (luma only) waveforms, reference white of 100% corresponds to a digital level of 235, an NTSC level of 100 IRE, and a PAL level of 700 mV. White excursions up to 108% are technically possible.
In Y (luma only) waveforms, reference black of 0% corresponds to a digital level of 16, an NTSC level of 7.5 IRE, and a PAL level of 0 mV. Black excursions down to -8% are technically possible.
With both white and black levels, further signal processing (down the line from your Avid system) might clip the peaks in your material. In addition, you might be required by delivery specifications to limit the white peaks to a lower level and the black peaks to a higher level.

Use Y Waveform to see the black and white levels of your image. Sometimes, particularly with white levels, keeping the white peaks within the 100% limit will not produce a pleasing level for the rest of the image. This is particularly common with backlit subjects, where the sky or a window is in the background and the lighting on the foreground is insufficient. In these cases, you might want to adjust for the foreground and leave the background too bright.
Chroma peaks are easiest to see on the vectorscope. The theoretical maximum is the circle around the outer edge, but to be safe you might like to keep vectors closer to the center than the 75% color bar squares.
Saturated bright or dark colors might have very low or high luma values, together with a lot of chroma. Even if neither luma nor chroma alone is excessive, the combination can be illegal. For example, vivid yellow and cyan in an image can produce composite levels that are too high, and those from vivid blue might be unacceptably low. The YC Waveform is a good way to see how far these levels extend. In general, avoid levels above approximately 120 IRE or 850 mV, and those below -20 IRE or -200 mV.
If you are producing a master for broadcast delivery, ask for delivery specifications. To ensure you meet particular standards, use a legalizer such as the Safe Color Limiter effect or a third-party AVX plug-in."

October 23rd, 2007, 02:52 PM	#1
Warren Kawamoto Trustee Join Date: Nov 2006 Location: Honolulu, HI Posts: 1,435	Legal color? The in "look" now is crushed blacks, oversaturated color, blown out highlights. These shots look really cool on computer screens and monitors. The problem is that we need to broadcast some of these shots on tv. Currently, our crushed blacks are at -10 IRE, and chroma and highlights are way over 120%, which is not broadcast legal. My question is: How can we maintain this "look" on broacast television and still be legal?

October 25th, 2007, 07:17 AM	#4
Vito DeFilippo Trustee Join Date: Mar 2006 Location: Montreal, Quebec Posts: 1,585	It's not a matter of 'compressing' the luminance. It's a matter of clipping outside values. The distribution of luminance values within the extremes stays the same, so the look stays pretty much the same. I'm a bit fuzzier on whether the same is true of chroma, so I won't speculate. Perhaps someone with more broadcast experience will chime in on that one. __________________ . http://www.nosmallroles.com

October 25th, 2007, 07:28 PM	#5
Vito DeFilippo Trustee Join Date: Mar 2006 Location: Montreal, Quebec Posts: 1,585	Warren, This is from the AVID help menu, if it's interesting: "Safe Color Limits with Waveform and Vectorscope Information To stay well within the limits of television transmitters, cable systems, satellite links, DVD encoders, and so on, broadcasters or distributors often issue safe color limits for video levels. Video levels outside safe color limits are generally known as "illegal." Of course, no law is broken if you exceed the specified limits, but the program might be rejected on technical grounds or the image quality might suffer with further processing. If you know that your delivery master is a VHS tape that does not handle high chroma well, set some reasonable limits by yourself. In Y (luma only) waveforms, reference white of 100% corresponds to a digital level of 235, an NTSC level of 100 IRE, and a PAL level of 700 mV. White excursions up to 108% are technically possible. In Y (luma only) waveforms, reference black of 0% corresponds to a digital level of 16, an NTSC level of 7.5 IRE, and a PAL level of 0 mV. Black excursions down to -8% are technically possible. With both white and black levels, further signal processing (down the line from your Avid system) might clip the peaks in your material. In addition, you might be required by delivery specifications to limit the white peaks to a lower level and the black peaks to a higher level. Use Y Waveform to see the black and white levels of your image. Sometimes, particularly with white levels, keeping the white peaks within the 100% limit will not produce a pleasing level for the rest of the image. This is particularly common with backlit subjects, where the sky or a window is in the background and the lighting on the foreground is insufficient. In these cases, you might want to adjust for the foreground and leave the background too bright. Chroma peaks are easiest to see on the vectorscope. The theoretical maximum is the circle around the outer edge, but to be safe you might like to keep vectors closer to the center than the 75% color bar squares. Saturated bright or dark colors might have very low or high luma values, together with a lot of chroma. Even if neither luma nor chroma alone is excessive, the combination can be illegal. For example, vivid yellow and cyan in an image can produce composite levels that are too high, and those from vivid blue might be unacceptably low. The YC Waveform is a good way to see how far these levels extend. In general, avoid levels above approximately 120 IRE or 850 mV, and those below -20 IRE or -200 mV. If you are producing a master for broadcast delivery, ask for delivery specifications. To ensure you meet particular standards, use a legalizer such as the Safe Color Limiter effect or a third-party AVX plug-in." __________________ . http://www.nosmallroles.com

October 24th, 2007, 08:31 PM	#2
Vito DeFilippo Trustee Join Date: Mar 2006 Location: Montreal, Quebec Posts: 1,585	Crushed blacks and blown highlights don't have to be outside legal limits. Some NLE's have effects that will make your levels legal, or in the colour correction tools will let you clip luminance above and below legal limits. I routinely clip above and below legal limits while I do my colour correction, though I could be much more anal about it than I am. The problem with using a legaliser effect on the whole timeline is that you then have to render the entire thing...

October 24th, 2007, 10:20 PM	#3
Warren Kawamoto Trustee Join Date: Nov 2006 Location: Honolulu, HI Posts: 1,435	Vito, Thanks for your reply. I can see "compressing" the crushed blacks and highlights to keep them within legal limits, but what about chroma? There is no way to de-saturate over-saturated color without losing the look. Or is there?