Different exposure when rendering different parts of the image

Use this forum for general user support and related questions.
alpistinho
Posts: 8
Joined: Thu Jul 05, 2018 11:38 pm

Re: Different exposure when rendering different parts of the image

Post by alpistinho » Wed Nov 14, 2018 3:32 pm

FXtend wrote:
Wed Nov 14, 2018 3:25 pm
How would it help to adjust both rather than just one?
I believe that after reversing the gamma for both sides they will be a multiplication away from each other.

So you would need to reverse the gamma for both sides, multiply one of them to make them equal and then apply the gamma correction again.

FXtend
Posts: 12
Joined: Tue Nov 13, 2018 7:20 am

Re: Different exposure when rendering different parts of the image

Post by FXtend » Sat Nov 17, 2018 4:13 pm

Thanks for all the feedback :)
I think I've found a solution. There's a little bit of overlap between the halves so I'm thinking that if I render a few pixels within that overlap without gamma correction I should be able to set up a system of equations. I tried without this extra render but then I got eight equations and eight unknown variables whereas this method should give me only four and, well, I'm lazy :mrgreen:
All I need to do is make sure that Auto Brightness is disabled, right?

User avatar
Dade
Developer
Posts: 1528
Joined: Mon Dec 04, 2017 8:36 pm

Re: Different exposure when rendering different parts of the image

Post by Dade » Sat Nov 17, 2018 4:30 pm

FXtend wrote:
Sat Nov 17, 2018 4:13 pm
All I need to do is make sure that Auto Brightness is disabled, right?
Yup.
Support LuxCoreRender project with salts and bounties

User avatar
FarbigeWelt
Posts: 344
Joined: Sun Jul 01, 2018 12:07 pm
Location: Switzerland
Contact:

Re: Different exposure when rendering different parts of the image

Post by FarbigeWelt » Sat Nov 17, 2018 4:35 pm

FXtend wrote:
Sat Nov 17, 2018 4:13 pm
All I need to do is make sure that Auto Brightness is disabled, right?
This is right. I would render a preview, adjusting brightness manually in linear tonemapper during rendering and then stop and restart wirh final resolution.

I am very curious how your rerender will top your already fantastic work.
Microsoft Windows 10 Professional, intel i7 4770K, 32 GB, AMD R9 290x 4 GB, AMD R9 390x 8 GB
Instagrammer, please join #luxcorerender for your renderings.

FXtend
Posts: 12
Joined: Tue Nov 13, 2018 7:20 am

Re: Different exposure when rendering different parts of the image

Post by FXtend » Sun Nov 18, 2018 3:21 pm

FarbigeWelt wrote:
Sat Nov 17, 2018 4:35 pm
This is right. I would render a preview, adjusting brightness manually in linear tonemapper during rendering and then stop and restart wirh final resolution.
Okay, I think you've sort of misunderstood my strategy. I don't want to rerender the full scene since I don't feel like waiting another month for my scene be finished. My idea is to figure out the gamma and gain by sampling both halves and a tiny render without gamma correction in order to set up a system of four equations that should give me the factor (gain?) and gamma value.
FarbigeWelt wrote:
Sat Nov 17, 2018 4:35 pm
I am very curious how your rerender will top your already fantastic work.
Thanks :) I think I'll top it by having the same gamma on both halves and applying some lens flares and color correction and stuff ;)

User avatar
B.Y.O.B.
Developer
Posts: 1806
Joined: Mon Dec 04, 2017 10:08 pm
Location: Germany
Contact:

Re: Different exposure when rendering different parts of the image

Post by B.Y.O.B. » Sun Nov 18, 2018 3:23 pm

Have you tried what alpistinho suggested?
Reverse gamma correction is just gamma correcting with gamma = 1/2.2.
alpistinho wrote:
Wed Nov 14, 2018 3:32 pm
I believe that after reversing the gamma for both sides they will be a multiplication away from each other.

So you would need to reverse the gamma for both sides, multiply one of them to make them equal and then apply the gamma correction again.
Support LuxCoreRender project with salts and bounties

User avatar
Racleborg
Posts: 208
Joined: Sat Apr 07, 2018 10:31 am
Location: UK

Re: Different exposure when rendering different parts of the image

Post by Racleborg » Sun Nov 18, 2018 3:53 pm

I don't want to rerender the full scene since I don't feel like waiting another month
A month!? That's a very long time. Is this usual for some scene types?

FXtend
Posts: 12
Joined: Tue Nov 13, 2018 7:20 am

Re: Different exposure when rendering different parts of the image

Post by FXtend » Sun Nov 18, 2018 5:45 pm

B.Y.O.B. wrote:
Sun Nov 18, 2018 3:23 pm
Have you tried what alpistinho suggested?
Reverse gamma correction is just gamma correcting with gamma = 1/2.2.
alpistinho wrote:
Wed Nov 14, 2018 3:32 pm
I believe that after reversing the gamma for both sides they will be a multiplication away from each other.

So you would need to reverse the gamma for both sides, multiply one of them to make them equal and then apply the gamma correction again.
That's what I'm trying to do but I need the gamma values and factors. That's what the equations are for.
I'm assuming Luxcore does gamma correction according to Image.
Maybe that's where I'm wrong because it still doesn't look good after solving the equations :?

FXtend
Posts: 12
Joined: Tue Nov 13, 2018 7:20 am

Re: Different exposure when rendering different parts of the image

Post by FXtend » Sun Nov 18, 2018 5:53 pm

Racleborg wrote:
Sun Nov 18, 2018 3:53 pm
A month!? That's a very long time. Is this usual for some scene types?
That is very long indeed. Keep in mind that most of the sunlight has to go through both the fog and the water where it's refracted and dispersed and bounce around inside the pipe. I mean, interiors can be heavy but I think I've created something extreme :mrgreen:
I don't know if this sort of render time should be considered acceptable still but that's all I know. Oh, and it's 4K.
Maybe I could have done with a little fewer samples...

User avatar
Racleborg
Posts: 208
Joined: Sat Apr 07, 2018 10:31 am
Location: UK

Re: Different exposure when rendering different parts of the image

Post by Racleborg » Sun Nov 18, 2018 6:43 pm

Well, it looks great! So if it takes a month, then it takes a month ;)

Post Reply