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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Highlight Roll-off

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Medavoym

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Hi!

On film, highlights are of course much better looking than on digital formats, because there is a built-in slight roll-off and therefore the clipping is much more pleasant.

Any tricks, suggestions, advice as to how to achieve this on RED? Especially in post, but also on set.

I assume that you have to leave a bit of a headroom on the right side of the histogram while exposing to be able to do something once grading. I would like to know more about what can be done in post to replicate the way highlights look on film. I'd appreciate any pointers from experienced redusers.

Thanks!
 
Redspace has some of this built in.

In post it's as simple as an s-curve.
 
For every stop you under-expose, you gain a stop of extra highlights. You can use that then, with an exposure curve, to smoothly roll off highlights. Don't take this too far, or the image will be too noisy, but get it right, and you'll get great looking footage.

Graeme
 
Graeme Nattress said:
For every stop you under-expose, you gain a stop of extra highlights. You can use that then, with an exposure curve, to smoothly roll off highlights. Don't take this too far, or the image will be too noisy.

Graeme
Click to expand...

Just so I get it right: smoothly rolling off highlights means pulling the values slightly down at the upper end of the curve. Right?...

Can anybody recommend a very good "grading with curves" tutorial? I am very new to this. I used to correct with Color Finesse and I used the HSL controls with a waveform. Even though the two methods obviously relate, I don't feel comfortable yet using the curves to do primary color correction.

PS Thanks for all the tips.
 
No, the curve bends up at the bright end, because you've made the overall image dark. You brighten it up, but you brighten up the highlights less....

Graeme
 
I think I understand. There are 3 control points on the curve. Basically, I pull up the upper one, I pull down the lower one and I don't touch the middle one (or just slightly). This way I create the S-shape.

Am I correct?

Weirdy, I feel like I'm starting again from zero when using the curves.
 
Yes, create an S-shape, but you should be under exposing, then using the curve to brighten the image back up, with this method.

Graeme
 
So this method doesn't work with "exposed to the right" footage (even when highlights are not clipped)?

Maybe that's what it is... I have some "exposed to the right" footage from someone. I know I have to bring everything down back to normal (the advantage being less noise), but I also want to have nice, rolled-off highlights. The clip does look overexposed overall, but there is a lot of room on the right side of the histogram.
 
Sure it works great with ETTR. ETTR means that there's no clipped highlights, therefore you need no curve to slowly roll them off.....

Graeme
 
Yes. I meant pulling up the highlight control button (it doesn't work with exposed to the right footage).

Basically with ETTR you just pull down the middle control button to bring everything down. You fiddle very little or not at all with the highlight button because you don't need to roll them off anymore...

I was confused - I though that no matter the approach (underexposed or ETTR) you do need to do something to roll off the highlights.
 
Highlight control is for making sure you get the full dynamic range from the sensor, in that highlight colour remains correct.

With highlights, you can only roll off highlights into clipping if they are not clipped. If they're clipped, they're clipped, and hence you can't roll them off. You can roll off the un-clipped regions into the clipped regions though.

Basically, to change from a linear distribution up to clipping, to a soft transition, the main body of the data needs to be less exposed so you can brighten it up, but use a curve so that the highlight region gets less brightened, giving a smooth rolloff.

Graeme
 
Graeme Nattress said:
Highlight control is for making sure you get the full dynamic range from the sensor, in that highlight colour remains correct.

With highlights, you can only roll off highlights into clipping if they are not clipped. If they're clipped, they're clipped, and hence you can't roll them off. You can roll off the un-clipped regions into the clipped regions though.

Basically, to change from a linear distribution up to clipping, to a soft transition, the main body of the data needs to be less exposed so you can brighten it up, but use a curve so that the highlight region gets less brightened, giving a smooth rolloff.

Graeme
Click to expand...

I know this has probably been discussed at length elsewhere, but Graeme do you see any sense in building-in a curve in the analog-to-digital conversion from the sensor in the camera? Would this sacrifice bit-depth? Is it even possible to fix a roll-off into the sensor? The only practical reason for this would be a better correlation between light meters and traditional film exposing on the Red, and not having to false-color every shot to make sure nothing is clipped. A bit of pre-S-curving on the top would be fine in my opinion, if it allowed for a more instinctive exposure.
 
For colorimetry you need entirely linear data. So the first thing you'd need to undo is the curve. Also, the sensor pixel itself is quite linear indeed, so over-all, I don't see it helping.

Graeme
 
Dear Graeme,

In the ETTR method, is it beneficial to leave some headroom on the right side of the histogram when exposing based on the RAW VIEW, or is it better go all the way to the right, without clipping, of course?

Especially since you say you don't have to do anything to the highlights in post, once you ETTR (you don't have to roll them off).

Is there any possible disadvantage when you ETTR as much as possible, right to the very edge (again, without going over)?
 
If I may chip in...

eastco said:
In the ETTR method, is it beneficial to leave some headroom on the right side of the histogram when exposing based on the RAW VIEW, or is it better go all the way to the right, without clipping, of course?
Click to expand...

I think it pretty much depends on the image, the contrast it has and what you want to do with it. There isn't a universal solution for every type of image IMO.

eastco said:
Especially since you say you don't have to do anything to the highlights in post, once you ETTR (you don't have to roll them off).
Click to expand...

I think Graeme meant you don't have to do anything to get roll-off if you captured all the data, but you still have to make a curve, otherwise your image will look flat if you used RAW view.

eastco said:
Is there any possible disadvantage when you ETTR as much as possible, right to the very edge (again, without going over)?
Click to expand...

If you're in the RAW view space and you need to do a specific s-curve while having highlights full the right, you'll burn them. If you're in the Redspace you already have an s-curve.
 
ETTR means just that. If you back away from the "edge" you're loosing dynamic range and are under-exposed.

Graeme
 
I most often ETTR to achieve the best SNR then, if needed, lower exposure in post in order to play with the relationship between highlights and my s-curve interactively.

Naturally, creative choices may dictate all manner of over/under exposure independent of a "perfectly" exposed image.

Michael
 
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