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Colour grading - avoiding noise / maintaining native ISO

Explorer ,
Mar 17, 2024 Mar 17, 2024

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Hey all, 

 

I'm colour grading some footage I shot in a native ISO function — therefore noise free. How much can I play around with the exposure sliders in Lumetri colour before I'll start seeing noise? What are some general rules on this matter? 


Thanks,

Fin

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Community Expert ,
Mar 17, 2024 Mar 17, 2024

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Perhaps a better question is what is your intent? And are you using the right methods and tools to achieve that?

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Explorer ,
Mar 17, 2024 Mar 17, 2024

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I'm trying to make some basic exposure changes for a short video. I exposed pretty well during my shoot but want to adjust in Lumetri, How much will these adjustments mess with my noise-free footage?

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Community Expert ,
Mar 17, 2024 Mar 17, 2024

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Did you shoot in log? Or standard profile? Noise-free is a bit of an overstatement, there's always noise. Depending on what you do to an image you may reveal camera noise and/or compression artifacts. Correcting for exposure by little amounts would never give such issues under normal exposed imagery though.

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Explorer ,
Mar 18, 2024 Mar 18, 2024

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Yeah I shot in Log. Thanks! I think that covers it. 

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Community Expert ,
Mar 19, 2024 Mar 19, 2024

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I'd add that since you shot in log there is actually a close to photographically accurate way to adjust exposure. Lumetri's exposure slider does two completely different things depending on which direction you slide it away from 0. It's primairily also designed with "normal" video in mind, not log footage. 

If you are using LUTs to convert your log footage to Rec.709 and you want to do it the proper way, put your LUT after your exposure adjustments. If you grade by directly applying the effects to the clips place a Brightness & Contrast effect before the Lumetri Effect on the clip. If using Adjustment Layers place the exposure adjustment layer below the LUT adjustment layer. Brightness will control the exposure, it's a bit sensitive so you may want to slide while holding down CTRL/CMD. And contrast = contrast. You'll find that this gives very accurate results even when going a bit more extreme. Lumetri's exposure slider on the other hand will not retain the same light ratios and severely increase or reduce contrast.

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LEGEND ,
Mar 19, 2024 Mar 19, 2024

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Shebbe gives great help. I'll add though that no camera is noise-free. There is always signal noise, and the camera processing is setup to minimize this as much as possible without doing worse damage to the image.

 

So depending on what changes one does, one can start showing visible noise with any camera. It's how you do your changes that may create less noise and artifacting than using the tools a different way. Taking practice and some experience to learn. But to me, that is a fun trip ... 😉

 

A color "surface" ... control panel, can make a huge difference in both the speed of what you do, but more importantly, the range of things you can do.

 

For example, manually normalizing log video to linear display space. Doing this in the Basic tab is actually pretty slick, working mainly two controls with and against each other. Therefore, if you can do them simultaneously, you can both work faster and see the interim states more clearly.

 

A Tangent Ripple is what, $350USD or so? Do much, that alone will pay for itself. I've both a full Elements panel in suite, and a Ripple for my laptop or on the road. Either way, I've remapped controls so the Basic tab controls are all ... simultaneously! ... on the ball & rings. One tool mapped for the ball's horizontal motion, another for the vertical motion.

 

My middle ball is Contrast. Both "contrast" and "saturation" are actually contrast controls, right? So my middle ball is mapped so that tonal contrast is set to vertical movement, saturation contrast is set to horizontal movement. Exposure is mapped to the ring for that ball.

 

So I'm working Exposure, Contrast, and Sat ... simultaneously. As one example of what a surface control can do. And yea, manually normalizing log footage is a breeze.

 

Shebbe is also right about the Exposure control dual types of movement. The Exposure control expands image contrast when going up, sorta like grabbing the White end point of the RGB curves tool, though with a roll-off on the white point. And as Shebbe notes, it's different going down ... a simple end-point pull down, no shape changes.

 

The Contrast control expands outward from, or in towards, the 50 IRE mid point of the Waveform or Parade scopes

 

Combine the two ... Exposure both increases overall 'contrast' while moving the center point up. Contrast moves out from the current center point. So use Exposure to set where you want contrast to expand from as the center, and Contrast to set the overall push out from that center.

 

You'll probably want a bit of Sat or Vibrance change to taste also, maybe do a slight trim with Shadows, Highlights, and Black control.

 

That's one way of working the process. And once you've got it to a setting you like, and works well on several images from that camera, SAVE that as a preset. Then when you get that camera in the future, in log, select all the clips in the bin. Drag the preset from the Effects panel to them, slam bang DONE. All normalized.

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