Aquiring the HDR Exposure value?

Development Rendering
1

I am looking to create a blueprint or post processing effect that acts based on the exposure in the scene.
For this i need the exposure value. I want to create more noise/desaturation when there are low light levels, just like with human vision.
However i cant seem to call the current exposure value.

I can read out this value when i Visualise HDR in the viewport, like here:

bpdf4em.png
bpdf4em.png920Ă—188 27 KB

Anybody got ideas on how to obtain this value from UE4?

2

Hello,
i am not sure that you will find there all what you need but… : Light problem in dark scene - Rendering - Unreal Engine Forums

in editor : show / visualize / hdr (as you know) and in post process volume : auto exposure.

Not sure if there is a way to have real time info in blueprint.

I tried in level blueprint : reference to post process volume / get settings / break settings, so it can be changed but not found a way to have value yet.

Edit : if you have no replies tomorrow, i’ll move this thread to rendering section to have more chances to find a solution.

3

hmm sad to see nobody knows a way to retrieve this value :confused:
ill have to figure some other way then…

4

Thread moved to rendering to help find someone with a solution.

Edit : i forgot to do it earlier. sorry.

5

Any Update?
I am looking for the same thing…

6

Massive bump, but I don’t think this has been discussed that much before so… do it by luminance with 0.2126, 0.7152, 0.0722 as the coefficients or use the EyeAdaptation node, which will give you the PreExposure Value from the HDR Histogram debug view. It will need to be remapped to 0-1 if you use it as a lerp alpha.

1 Like
7

Could you give me some example please?
I am trying to get that value from a Camera and store it in Blueprint.

8

Same problem.

I tried in c++ with FSceneView::GetEyeAdaptationTexture() but don’t work like I want and seems very heavy to have a simple value.

9

I have a thought that might work but it is an absurdly stupid approach…

You can retrieve the EyeAdaptation value from the material graph, output it to the emissive and draw it to a 1x1 render target every frame, then sample the render target in a Niagara particle emitter and export the data to Blueprint…

A smarter way to do it would be to retrieve the eye adaptation value directly from Niagara and export it to blueprint although I’m not entirely sure how to do this, I think it should be possible… That way you can avoid the nonsense of drawing/sampling a render target

1 Like
10

I try this too but when I draw a material to a render texture the EyeAdaptation it always be equal to 1 :confused:
I thought it was because the value was clamped by the texture but no

11

Thats unfortunate :frowning: I’m wondering if maybe it uses the rendering cameras exposure…

Sorry, that was my only idea :confused:

12

I don’t understand why Epic does not expose this value. It could be very useful for create some cool features in our games, like set the amount grain and motion blur founction of exposure to make a crealistic camera effect !

13

Hi there,

did someone manage to get a solution here ?

I’ll be needing to acquire this value too.