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Weird black level clipping
Hello everyone,
I’m color correcting a piece in FCP using 1080 23.98 footage from HDCam. At first I digitized at 8 bit uncompressed 23.98 using a Kona 3 card and a SONY HDW-F500 deck. When I got to color correcting I noticed that some of the clips had black levels falling under 7.5 ire but above 0 ire on my external scopes. To deal with these I used the 3-way color corrector to bring the black lower limit to the 7.5 mark, but when I rendered I got unexpected results. My rendered clips would end up with a lower limit well above 7.5 ire and much of the black information was clipped. It’s as if the system FIRST clipped everything under 7.5 AND THEN applied my correction which brightened the dark video.
I looked at all my settings, trashed prefs, tried many different combinations of clip settings versus sequence settings but everything yielded the same results.
Finally, I tried re-digitizing using Prores422 and thankfully my corrections rendered correctly, meaning that my rendered clips had their blacks (which originally fell below 7.5 on my scopes) pushed up to 7.5 without clipping.
Can anyone explain this? I have a feeling that this has something to do with RGB vs. YUV spaces. Regardless, I don’t want to be forced to use Prores on every job.
Thank you,
Roman -
2 Replies
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[Roman Hankewycz] “When I got to color correcting I noticed that some of the clips had black levels falling under 7.5 ire but above 0 ire on my external scopes.”
WHY are you destroying your footage?
HD levels are always set to 0
7.5 IRE is for analog SD ONLY
gary adcock
Studio37
HD & Film Consultation
Post and Production WorkflowsInside look at the IoHD
https://library.creativecow.net/articles/adcock_gary/AJAIOHD.php -
Good point although a little presumptuous. My scopes are hooked up to a down-converted SD SDI signal from my Kona3, and my Kona is configured to build in the 7.5 setup on down-convert. So when I say 7.5 ire on the scope, that is the same as saying 0 inside FCP. It’s true that this isn’t the ideal monitoring set up but it does for now.
But your comment brings up a more interesting point. If 0 in FCP is displayed as 7.5 on my scopes, and I was seeing levels of 0 on my scopes, then doesn’t that mean that my clips inside FCP had levels below the digital 0 mark? Is that possible?
Not to mention the most important question of all: Why was back info clipped from my rendered video?
Again I will give an example. If I played one of my clips with no filters put on, I would see the black limit of the video signal reach 0 ire on my external scopes. However, if I applied any filter to the clip, even without adjusting any of the filter’s settings so as not to effect the footage, after rendering everything under 7.5 ire on my external scopes would be clipped. Why?
Roman
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