Reliable broadcast colors possible?
by Roland Pfisterer
on
Jun 16, 2009 at 2:47:39 pm
Hello everyone,
about to add some more confusion to the neverending story of broadcast safe colors.
Just to give some background info for my question: I work for an animation company, we only deliver digital material to post houses which do the conversion to tape. So I don't need to worry about making the video signal broadcast safe, but I'd like to make sure that there are no huge color changes from what we deliver to the final broadcast.
We don't have the hardware to check actual video levels (yet), and it seems that getting this equipment just to be sure is unnecessary.
In search of a reliable software solution I tested the broadcast color correction of Shake, After Effects and Color Finesse, and they all flag different colors/ranges as inappropriate, with Shake complaining about the least, AFX correcting pure magenta which CF doesn't do, and CF correcting pure blue which AFX doesn't do. The settings were the same as far as possible.
I know that none of them might be perfect for correcting colors, only for identifying which colors have to be corrected. But can anybody say which of them, if any, does that reliably? Is there some other software to look into for this? Or is there no such thing and we do need to get a vectorscope after all?
Re: Reliable broadcast colors possible? by Joseph Owens on Jun 23, 2009 at 1:17:04 am
There are some "grading" monitors that have scopes built into them -- very few have gamut warning systems, though. Fewer that are actually useful and/or accurate.
You're right about different systems flagging different things because there are different issues with the component video streams and colourspaces themselves. What is "legal" gamut in RGB may not make the trip in YCbCr, and may not be compatible with YIQ ("composite broadcast").
In RGB its virtually impossible to have zero luminance (only one combination, R=G=B=0), but you can do that with many combinations of colour components in both YCbCr and YIQ or YUV, which can also generate negative values, easily. To adequately monitor "Broadcast Safe", you really need a system that is looking at composite emulation, where the additive effect of luminance and chrominance are being evaluated. Innocent amounts can combine to put you out of bounds. You are allowed up to 102 IRE in luminance and up to 120 IRE Y+C... but for example, 20 units of yellow, for instance is going to put you over, and that's only half of a "normal" amount of saturation corresponding to 40 IRE burst. You can't even generate that in RGB, but it would be trivial in a grading application working in YCbCr.
Re: Reliable broadcast colors possible? by Roland Pfisterer on Jun 24, 2009 at 1:44:23 pm
Thanks for the reply! Of course this sparks even more questions...
I have read this several times now that certain combinations of color and brightness "can" combine to illegal values in the video signal. But wouldn't this always be the same combinations that convert into the same illegal values? Or is there some other influence? Because if not it should be no problem to look at the color values in a software and determine if they will be out of bounds as a video signal, even considering different conversion standards. They would have to be selectable of course.
Otherwise I wonder what these broadcast safe plugins actually do and assume when they flag values as illegal.
Another thing is that we are only working in RGB. Somebody else told me it would actually be impossible to generate any illegal values in RGB as long as you stay in the range of 0-255, i.e. no superblack or superwhite. Does that make sense then? Btw this concerns PAL country only.
