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black levels below 0 IRE
This is something I’ve grappled with for quite some time without ever taking the time to get to the root of the problem. Final Cut once upon a time didn’t do this, right?….
Unrendered clips luma all stop at zero, but once rendered, can fall below zero (on the internal scopes). Sometimes it is hard to figure out how to get the right color correction and also not drop below zero. I got stung this year with a graphic in a Q/C for PBS. Broadcast filter does not address this (does not have 0 clamp; also, unrendered, nothing every falls below zero anyway).
I’ve seen this on imported clips, graphics, mattes, text, vignettes, nests — almost anything with more than simple use of one or two filters; occurring in every codec, well, at least DV, ProRez and uncompressed.
Thoughts? Intel duel quad, FCP 5 and FCP 6 boots, Black Magic / Decklink.
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6 Replies
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First off, Bill, I loved the Lost Skeleton of Cadavra. In any event, I had this issue recently with a program for History. Some DV evidence footage had blacks that would dip below 0 once rendered in our prores sequence, despite them have the Broadcast Safe filter set to “Extremely Conservative”.
I think it has do with the FCP’s RT Extreme downressing the clip for playback, that was causing the internal waveform and vectorscopes to not see all the luminance information. The bummer is that it required me to render those clips, adjust the blacks, and then rerender again to make sure I boosted them appropriately. It’s not elegant, but it worked.
Otherwise, you might also consider a Harris DL 860.
Richard Sanchez
North Hollywood, CA“We are the facilitators of our own creative evolution.” – Bill Hicks
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Yay, a Skeleton fan! We had an American Cinemateque screening for “… Returns Again” just three days ago: https://lostskeletonreturnsagain.com
Yeah, the broadcast filter seems to only pay attention to the top of the levels. Since rendered footage can differ from unrendered, and the broadcast filter assesses unrendered conditions, I have had the broadcast filter fail me before for Q/Cs, even the color mashing “extremely conservative”. Sigh — we need a simple software black clamp option or filter of some kind. Oh well.
Thanks, Richard!
“THE LOST SKELETON OF CADAVRA” –
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Once again Broadcast safe filter doesn’t seem to work post render.
I have long ago swapped to RGB limiter which certainly works for peak white clamping. So far I haven’t had a tech reject for sub blacks. As I am delivering finals to broadcasters, the RGB limiter set conservatively for peak whites and chroma is on every clip and so far has kept me legal.
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Doing! Lookie there, a black clip. And it works. I’ve never paid attention to that filter. Thank you, that’s the ticket!
“THE LOST SKELETON OF CADAVRA” –
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We had far too many problems with blacks dipping below 0 in FCP even after using the Broadcast Safe filter. These were archival BetaSP tapes that mostly bit us in the behind. The occasional graphic as well. After getting rejected by QC one too many times we bit the bullet and picked up the Harris DL-860. Works like a champ.
We’ve even seen luma+chroma clips that no matter how you tried, you just couldn’t bring into legal spec with the 3 way CC filter, but the DL-860 worked it’s magic on. The DL-860 looks much cleaner as well.Michael Alberts
Ambidextrous Productions, Inc.
http://www.ambidextrous.net -
Broadcast safe does not protect the blacks as you have found. It really only works on the highlights.
You need to use the Levels Filter to clip the blacks. Or better yet, use Color.
We’ve delivered over 100 HD masters to networks and have never had a show rejected for video levels. I have no idea how many BetaSP masters we’ve delivered over the past three years but I believe we’re up to 150 news stories and nothing rejected there either.
We use nothing but FCP, Color and sometimes Colorista for all color grading and broadcast safe.
Walter Biscardi, Jr.
Biscardi Creative Media
HD and SD Production for Broadcast and Independent Productions.STOP STARING AND START GRADING WITH APPLE COLOR Apple Color Training DVD available now!
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