Light Group really helps in adjusting many lights in compositor, but after the exposure adjustments in the compositor, how do you retrieve the adjusted wattage of the lights?
This is so that you can do away/remove the adjustments in the compositor since the light will now have the corrected value.
Corona renderer have something like this, where after the realtime adjustment in the corona render buffer, you hit a button that’s name maybe, I don’t remember “set light values” and the adjustments change back to zero because the corrected light values are updated.
Well, the idea is that you wouldn’t need to do this, with how Blender is designed.
You would usually adjust all your lights directly in render preview, that’s why Blender has such a robust render preview mode.
The compositing option is there to get you out of trouble if you need to change a light after the fact and don’t want to re-render. But that’s mostly the workflow you use if you aren’t in charge of the project’s look and might be told to change something at any time.
If you know by how much you altered the light group’s intensity, I guess you could try to apply the same multiplier to the light itself, though I am not sure if the result will be identical, considering there’s a color transform on the image. I would just go by eye, again this should be easy thanks to Blender’s robust render preview.
What you say here does make sense in that there is a reason why the preview is “almost” real time now.
As for your “If you know by how much you altered the light group’s intensity, I guess you could try to apply the same multiplier to the light itself”, I don’t know what is the exact correlation between adjusting the exposure value in the compositor to returning that value back to the actual light’s wattage itself, that is actually my key question here
It sounds like you’re using the Exposure node to adjust your light values? The node’s slider is measured in stops, and the math for an exposure adjustment in stops is X * 2^stops — e.g., raising the exposure by one stop means multiplying the value by 2 (2^1); lowering the exposure by 0.7 stops means multiplying by approx. 0.6156 (2^-0.7).
There’s no inbuilt option to propagate your values back to your scene lights — partly because Blender doesn’t have a dedicated “light mixer,” where the light passes are adjusted in predictable ways: when the compositor setup could be using anything from Color Correctors to Mix Colors to AlphaOvers to Math nodes to custom node groups, finding a universal way to magically convert that all back into simple adjustments that can be applied to each light would be… difficult — but yes, if your changes are simple multiplications (brightening, darkening, adjusting the RGB weights), then copying them back to your lights will produce an identical result.
You…are a genius…now if someone could make a small utility program where you can enter the light’s original intensity and how much exposure you have changed in the compositor and tell you the final using your magical math numbers ;p
