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4k to HD path issues

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Glenn Sakatch
4k to HD path issues
on Aug 11, 2018 at 3:43:09 pm

I'm having a bit of an issue with a 4k to hd conversion.

-Program lives on my box in 4k with all the different camera raw clips. Full 45 broadcast show.
-because of the length and complexity of the grade, I have been outputting DPX10 bit sequence files along the way to keep a final rendered 4k version always at hand. If I have to tweak a shot, I simply re-render that shot to the dpx folder, and my dpx output timeline is automatically updated. This prevents me from having to re-render the entire show every time there are tweaks. Has been working well for approvals and promo sections, and all the other output requests...or so I thought.

If I bring those 4k dpx's back into my original 4k timeline, everything matches up. I can't tell if I'm looking at the original clips, or the 4k rendered clips.

If however, I switch my timeline down to HD, I have a noticeable difference in shots that utilize a heavy vignette effect. Shots without the vignette are matching up perfectly. (The 4k dpx's appear lighter in the vignette area than the original shots underneath.)

If I output a 444 4k quicktime movie, I get the same result. Perfect matchup on 4k timeline, but a weaker vignette when I switch to HD.

If I set my timeline to HD, and render out a quicktime, and bring that quicktime back in, it matches perfectly to the original timeline, but obviously not to the dpx or hd downconverted 4k versions.

So what is Resolve doing when it is converting these 4k files down to HD, that it isn't doing with the original timeline clips? Again, the difference is only noticeable on the vignetted shots, so it is not a full vs video levels issue.

The vignette in question is a stock Boris fx, not a home made vignette created in Resolve. (I may try to test those results as well)

I was really hoping to create a single 4k dubmaster, but I'm afraid i'll have to make both HD and 4k dubmasters to keep the versions consistent.

any suggestions are welcome.

Glenn


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Andi Winter
Re: 4k to HD path issues
on Aug 11, 2018 at 4:56:49 pm

never had this issue. the 4k downscaled movie should look exactly the same from dpx or original.

think it has to do something with your boris vignette! btw: why using a plugin for a vignette?


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Glenn Sakatch
Re: 4k to HD path issues
on Aug 11, 2018 at 5:42:44 pm

that is another story altogether ☺

I'll try some tests with a homemade vignette and see what happens.

Glenn


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Marc Wielage
Re: 4k to HD path issues
on Aug 12, 2018 at 2:49:46 am

Is it possible you have cache on and you're seeing a cached clip and not the original?

I'm not convinced what you're doing is an effective workflow -- rendering parts of the show as you go -- but if it works for you, no problem. The issue I see is that you're going to wind up doing quite a bit of the work twice (or more than twice). I'd rather just render it all once at the very end.


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Glenn Sakatch
Re: 4k to HD path issues
on Aug 17, 2018 at 12:18:48 pm

It's not a cache issue... outputs are all set to ignore the cache. It does seem to be a flaw with the settings in the ofx plugin I'm using. Absolutely everthing else matches perfectly.

I've rebuilt the FX by hand, and everything looks correct.

For what it is worth, the dpx workflow is actually quite handy. Some of the looks in this show are brutal on the box to render out, and render flashes at the end of a 20 minute segment are not uncommon...or even 1 frame in the middle of the segment.

Rendering to quicktime means trying the render again...after discovering there was a flaw, hoping it will work this time, or rendering those flawed shots, and piece mealing the show back together from multiple render passes.

With DPX, you render once into a folder. If there is a flaw, you re-render that shot into the same folder, it over writes the flawed frames. (you can even tell it to just render the 1 bad frame)

in the meantime, there is another timeline with the dpx's forming the program. This timeline is constantly updated with the current dpx renders. I can then use it for all the deliverable requests without fear of render issues...its just a downconverted dub at that point.

This workflow has actually saved me hours of render time in the creation of the 4k Master. If I had to completely re-render the 4k versions of these shows out evertime there was a render issue, I would probably be selling ties at Eatons by now. (Retro Canadian reference for those of you wondering)

Glenn

Glenn


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