DaVinci Resolve Forum
Broadcast Safe
Broadcast Safe
by Dan Johnson on Mar 1, 2016 at 2:01:36 am

I only work on projects for the web, but need to get a project broadcast safe so this is new ground for me. I watched this tutorial: https://www.youtube.com/watch?v=XSA_o1ojrZc The tutorial goes over what makes saturation go out of broadcast safe and how you can apply a broadcast safe filter. Is that all I need to do? Does the broadcast safe setting in the project settings only effect the saturation? Or does it also effect the luma value? If it doesn't what should I make sure my waveform looks like to make sure it is broadcast safe?

Re: Broadcast Safe
by Marc Wielage on Mar 1, 2016 at 8:26:39 am

Patrick does a good job and MixingLight has terrific tutorials.

My tactic is both to use the built-in clipper to limit the excessive white/chroma peaks, but also keep a close eye on the show while you're correcting. It's better to use curves or manual gain/desaturation controls to control the levels rather than let the clipper do all the heavy lifting.

Note that even the hard clip within Resolve will not always stop a really egregious blast of chroma. The hardware clippers were traditionally used in broadcast (sometimes at the transmitter) to stop these problems before they happened. Software clippers in my experience are good but not quite up to that.

If you want to see what the various settings do, set up a given adjustment and then crank on the levels and watch what happens on the scopes. Note that the manual says:

The clipping imposed by Broadcast Safe itself does not have an inherently soft roll-off. For best results, Broadcast Safe should be used in conjunction with the Soft Clip controls in the Color page, or a Soft Clip LUT.

I have had situations where I've had to drop a high soft/white clip curve as a Timeline node just to control these situations. I don't use it all the time, but if you're up against a deadline and have to get some dodgy material "air worthy," it can work.

Re: Broadcast Safe
by Dan Johnson on Mar 1, 2016 at 4:06:27 pm

Thanks for your help. Just for clarification since I'm feeling out of my league. On the Waveform monitor noting can go above 1000 right? What about 0? Attached is a still grab from my Waveform monitor. Would this pass or is around 0 a problem?

Re: Broadcast Safe
by Joseph Owens on Mar 1, 2016 at 9:36:41 pm

The real issue with respect to "Broadcast" legal gamut is that no RGB display will give you a true representation of where your luma + chroma values are going to wind up after matrix and baseband composite are computed. There are a few outboard scopes that have built-in functions to simulate the values that will result. The notion that simply limiting RGB values to between 0-100 complies to "legal" gamut is not correct.

Your example and query about the clipping in the blue channel depends on whether those values are truly clipped, or will result in *yellow-blacks* below 0 IRE and whether those will be passed through a composite baseband encoder. Those would be out-of-gamut values.

In reality, there are separate parameters for luminance and chrominance legal gamut boundaries. For Y', usually -2 to 102 IRE are permissible, and 75 to 100% saturation (while not maybe advisable, anyway) are the outer limits for chromaticity. In no event though are a combination of Y+C permissible beyond -20 and +120 IRE -- and this is the combined baseband signal that no software scopes are likely even capable of displaying.


"I always pass on free advice -- its never of any use to me" Oscar Wilde.

Re: Broadcast Safe
by Peter Chamberlain on Mar 2, 2016 at 12:48:22 am

If you set the Show Broadcast Safe Exception to on in Resolve you can see which parts of the image need adjustment. Turn on Broadcast Safe in Project Settings. We do a number of calculations to correctly represent the resultant composite image in the UI display and limits.

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