Different exposure when rendering different parts of the image

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FXtend
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Different exposure when rendering different parts of the image

Post by FXtend » Tue Nov 13, 2018 3:29 pm

My render seems to always crash after about a week of rendering so I decided to split it in two parts. This obviosly solved the problem since I've been able to let it run for more than two weeks without any trouble. However, when I brought the two parts into After Effects for compositing, I realized that there's a huge brightness and color difference between the two parts. I assume that this is caused by some sort of auto exposure in Lux.

So, my question is this: is it possible to find out the exact exposure difference between the parts and what's the best (preferably mathematically correct) way to fix it in post? I've played around with exposure, brightness/contrast, curves, tint and hue/saturation in AE but it always seems too dark in some places or too bright in others :|
Both parts were saved as exr.
ExpDiff.jpg

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B.Y.O.B.
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Re: Different exposure when rendering different parts of the image

Post by B.Y.O.B. » Tue Nov 13, 2018 3:54 pm

Which tonemapper did you use?
If you don't know, you can upload the .cfg or .blend file.
Also, which version of Lux? Did you use the Blender addon, or some different solution?
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Dade
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Re: Different exposure when rendering different parts of the image

Post by Dade » Tue Nov 13, 2018 3:56 pm

FXtend wrote:
Tue Nov 13, 2018 3:29 pm
So, my question is this: is it possible to find out the exact exposure difference between the parts and what's the best (preferably mathematically correct) way to fix it in post? I've played around with exposure, brightness/contrast, curves, tint and hue/saturation in AE but it always seems too dark in some places or too bright in others :|
Both parts were saved as exr.
Are you using Auto-Linear tone mapping ? In this case, it auto scales the image luminance and it explains your result. You should have used Linear tone mapping with the same user defined scale for both renderings.

To merge your already rendered images, it should be possible to scale up/down on of the half images to match the other half. Auto-Linear tone mapping just multiply the RGB values for a constant. It should be possible to multiply again one of the half-images for another constant to match the value used in other half.
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FXtend
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Re: Different exposure when rendering different parts of the image

Post by FXtend » Tue Nov 13, 2018 6:07 pm

Dade wrote:
Tue Nov 13, 2018 3:56 pm
Are you using Auto-Linear tone mapping ? In this case, it auto scales the image luminance and it explains your result. You should have used Linear tone mapping with the same user defined scale for both renderings.
Yep, linear with auto brightness :|

Dade wrote:
Tue Nov 13, 2018 3:56 pm
To merge your already rendered images, it should be possible to scale up/down on of the half images to match the other half. Auto-Linear tone mapping just multiply the RGB values for a constant. It should be possible to multiply again one of the half-images for another constant to match the value used in other half.
Thanks for the maths :)
I tried multiplying the brighter half with different shades of grey but I still have the same issue; some parts are too bright while others are too dark and the seam is clearly visible :?

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Dade
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Re: Different exposure when rendering different parts of the image

Post by Dade » Tue Nov 13, 2018 8:42 pm

FXtend wrote:
Tue Nov 13, 2018 6:07 pm
I tried multiplying the brighter half with different shades of grey but I still have the same issue; some parts are too bright while others are too dark and the seam is clearly visible :?
Efff, unfortunately, my original post wasn't accounting for gamma correction: it makes the process not linear. So you would have to reverse gamma correct the half image and, only after that step, you can scale the image and than gamma correct again. Sadly, this is a very complicate process because, like said, it is not linear and it is very hard to adjust accounting the gamma correction step.
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Racleborg
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Re: Different exposure when rendering different parts of the image

Post by Racleborg » Tue Nov 13, 2018 9:14 pm

The scene looks incredible! The bee, the flower, the lighting - wow!

I'd really like to see it when it's finished.

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Dade
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Re: Different exposure when rendering different parts of the image

Post by Dade » Tue Nov 13, 2018 10:05 pm

Dade wrote:
Tue Nov 13, 2018 8:42 pm
Efff, unfortunately, my original post wasn't accounting for gamma correction: it makes the process not linear. So you would have to reverse gamma correct the half image and, only after that step, you can scale the image and than gamma correct again. Sadly, this is a very complicate process because, like said, it is not linear and it is very hard to adjust accounting the gamma correction step.
Well, you can reverse gamma correct both half so you can match one luminance scale with the other.
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Sharlybg
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Re: Different exposure when rendering different parts of the image

Post by Sharlybg » Tue Nov 13, 2018 10:25 pm

Anyway your image look already unbelievable can't wait the end ;)
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FXtend
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Re: Different exposure when rendering different parts of the image

Post by FXtend » Wed Nov 14, 2018 3:25 pm

Dade wrote:
Tue Nov 13, 2018 10:05 pm
Well, you can reverse gamma correct both half so you can match one luminance scale with the other.
How would it help to adjust both rather than just one?

FXtend
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Re: Different exposure when rendering different parts of the image

Post by FXtend » Wed Nov 14, 2018 3:31 pm

Racleborg wrote:
Tue Nov 13, 2018 9:14 pm
The scene looks incredible! The bee, the flower, the lighting - wow!

I'd really like to see it when it's finished.
Sharlybg wrote:
Tue Nov 13, 2018 10:25 pm
Anyway your image look already unbelievable can't wait the end ;)
Thanks guys :)
Really appreciate that after all the trouble I've had with this scene.

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