Different exposure when rendering different parts of the image

[FXtend]

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.

[B.Y.O.B.]

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?

[Dade]

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.

[FXtend]

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

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

[Dade]

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.

[Racleborg]

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

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

[Dade]

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.

[Sharlybg]

Anyway your image look already unbelievable can't wait the end

[FXtend]

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]

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

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

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.