Change exposure 1 stop in Davinci Resolve

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dmitrizigany

Veteran
Hey!

I want to modify a LUT creating a -1 version for use on the 7Q so it looks correct when over exposing one stop.
I'm new to Davinci Resolve and it's just too much to take in. All I need to now is how do I change the exposure by one stop (or 2 for that matter)?

There's the offset wheels but it starts at 25. Twenty five what? How much should I turn it so it's a one stop difference?

Sorry for newbie question. Have no real plans of using Resolve at this time for anything other than modifying LUTs in this way, so don't have the time to wade through tutorials...

Thanks
 
Davinci Resolve measures in IRE. You should be measuring IRE on your waveform in DR. I don't think there is a way to calculate in F-stops...
 
markfpv said:
I'd suggest looking into LutCalc if that's is all you want / need to do. Probably more than one thread on here about it... but here's the first one I found:
http://www.dvxuser.com/V6/showthread.php?338018-Important-LUTCalc-Update&highlight=lut+calc
Click to expand...
I'll look into that...

scorsesefan said:
Davinci Resolve measures in IRE. You should be measuring IRE on your waveform in DR. I don't think there is a way to calculate in F-stops...
Click to expand...
Yeah, want to convert LUTs so they look right when being over exposed by one or two stops. Was hoping there was an easy way to achieve that, but looks like not. ;)
 
There's more to it than simply darkening everything. This is because there is an exposure curve that effects highlights, midtones and shadows differently. There's some subtlety here.
 
I started to realise that.
hmm. Would it be technically possible to add a function to the CD LUT utility app to automatically create -1 and -2 versions as an option? That would have been amazing! (I'm afraid I'm also too optimistic)
 
I assume the OP wants to open the lens aperture 1 stop wider on the camera for a shallower depth-of-focus, without altering the shutter speed to compensate, and then correct that over-exposure in post.

Just a guess.
 
If you are shooting a raw or log format or film stock, etc. ... over-exposing is , or at least can be, rating your camera's ISO's sensitivity less than it is - thus getting cleaner, less noisy darks.
Dmitrizigany - don't want to speak for Mitch - but pretty sure CD has some exposure compensated (-1, etc) luts already available for download on their web site...
 
If you are shooting a raw or log format or film stock, etc. ... over-exposing is , or at least can be, rating your camera's ISO's sensitivity less than it is[/QUOTE]

How so?
Click to expand...
 
I'm probably not the best person to explain this... but here goes. I'll stick to explaining shooting slog with Sony's Slog3.cine on the FS7 since it's the log format I'm most familiar with...
The log image on that camera is always recorded at the camera’s base ISO - in this case at ISO 2000 - recording the camera's full dynamic range - in this case 14 stops. If I decide to rate the camera at ISO 1000, that's one stop of less light sensitivity on the sensor and I need to open up 1 stop - all other camera settings being equal. (not going into any methods for determining the scene's correct exposure or losing possible headroom) But I'm effectively shifting the grey point in the scene up 1 stop to reduce noise - so when the footage is "pulled" down in post (and this is not "fixing" in the old Rec709 sense and that I'm also not "overexposing" in the normal Rec 709 video levels sense ) the shadows and darker area's of the scene I recorded will be less noisy and "cleaner".
This is similar to the way developing labs treated film stocks - if a DP rated the camera at a different ISO than the stock he was shooting. I believe Red's camera's have a bit different system for digital ISO ratings....
http://www.red.com/learn/red-101/iso-speed-revisited
 
Shooter said:


How so?
Click to expand...

The thing about ISO exposure - whatever - is that for formats that are dealt with in post there is only noise and headroom to be considered

iso and the like are therefore kind of arbitrary - or rather specific to the scene dynamic range - an manufacturer ISO rating is therefore built around a set of assumptions about your scene that may not be true
Click to expand...
 
Shooter said:
Why dont you just expose correctly?
I dont see the point of a general "over expose one stop" then fix it in post routine.
Click to expand...
Because even expose-purists like Alister Chapman recommends overexposing SLog by 1-2 stops to reduce noise etc. If I have a LUT that is compensated for that it's easier to see what the final image will look like.
 
markfpv said:
I'm probably not the best person to explain this... but here goes. I'll stick to explaining shooting slog with Sony's Slog3.cine on the FS7 since it's the log format I'm most familiar with...
Click to expand...
Unfortunately the FS700 doesn't have the Exposure Index function of the FS7...
markfpv said:
Dmitrizigany - don't want to speak for Mitch - but pretty sure CD has some exposure compensated (-1, etc) luts already available for download on their web site...
Click to expand...
Yes, they do. But what I would like to do eventually is to use a LUT that is very close to the final look I'm after and then be able to light and expose especially for that look...
 
Last edited:
dmitrizigany said:
Hey!

I want to modify a LUT creating a -1 version for use on the 7Q so it looks correct when over exposing one stop.
I'm new to Davinci Resolve and it's just too much to take in. All I need to now is how do I change the exposure by one stop (or 2 for that matter)?

There's the offset wheels but it starts at 25. Twenty five what? How much should I turn it so it's a one stop difference?

Sorry for newbie question. Have no real plans of using Resolve at this time for anything other than modifying LUTs in this way, so don't have the time to wade through tutorials...

Thanks
Click to expand...

set your project to ACES
use the correct IDT
use the correct ODT
set the first node's color science to l*a*b*
red offst now controls exposure
green offseet now controls midrid (tint) scale
blue offset now controls kelvin (temp) scale
import a wege test
save a still
split screen the still
adjust red offset (exposure) values until a one stop diffrence appears

note that many other controls will not react as expected, and it is possiable to create negitive pixel values using this method, so other than testing exposure, tint, temp it's not an easy tool set to work with
 
Dermot said:
set your project to ACES
use the correct IDT
use the correct ODT
Click to expand...
Haha, I'm already lost.
So clearly making them myself is too complicated at this point.

So now my hope is that CD add some sort of functionality either in the LUT Utility App or directly in the 7Q that allows any LUT to be monitored at -1/-2. But sounds like that won't really be possible either.
 
dmitrizigany said:
I started to realise that.
hmm. Would it be technically possible to add a function to the CD LUT utility app to automatically create -1 and -2 versions as an option? That would have been amazing! (I'm afraid I'm also too optimistic)
Click to expand...
No, these things cannot be done automatically because there is subtlety involved based on an exposure curve and other aspects. Just making something darker is not the same.

There are two reasons for overexposing in camera and then darkening in post. The first and most obvious to many is noise. Any noise in the darkest parts of the image will be made darker and therefore less noticeable. The second reason is bit depth. The lower in brightness the fewer bits are used to describe that part of an image. By making everything brighter in camera, more bits are used to describe the image. When darkened in post the parts of the image with the least amount of information are pushed down into darkness. Among other things, this helps prevent banding in shadow areas.
 
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