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Re: Broadcast Safe

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Joseph Owens
Re: Broadcast Safe
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.

jPo

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


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