I’m wondering if its possible to setup comp nodes so that I can easily adjust the white balance in my scene. I control my lights using blackbody based colors (i.e. warm interior lights @2-4000K, white sun @5-6000K, and cold sky 8-10000K). What if I now wants to balance for indoor, making my indoor appear more white - pushing everything else more to the right? Or balance for sky as neutral white, pushing everything else to the left? I noticed blackbody node is missing from the comp nodes, so I have no idea where to even begin. Is this possible at all in Blender?
In the real world you would indeed white balance the camera off a white or neutral 18% grey card. This would effectively set the white point to compensate for any excess in a particular colour channel. There are a number of ways to do this in Blender, in the compositor or the VSE.
The way David mentions is definitely the easiest way, but here’s yet another simple way to fix white balance. This demo is in Adobe Premiere, but you can easily do it in Blender with a Mix node set to Divide.
The divide trick was neat, I could always render a box with a white/gray rectangle to grab my reference from, and re-render without it. But I was thinking more of a fixed add/subtract shift in Kelvin from a known reference.
But it depends on what the main reflected source of the image is. You cannot easily determine the mix of colour temp unless you sample a diffuse incident of the scene.
If shooting the real world you could:
a/ sample reflected light from a white/grey card
or
b/ cover the lens with a diffuse translucent white cap, sample the light falling upon it.
Most of the time a film crew would shoot a slate/clapper board with a chip chart in the main field of view. This would occur at the start of the take. Perhaps you could insert your reference card at the first frame of animation too, except I doubt you would need the full resolution to get a colour sample.
Perhaps a simulation of the incident cap would be in order, that is a heavy blur of the input image and a normalisation of result.
Nope, my head is a leaking sponge… maybe its early Alzheimers? But now I understand why I keep asking the same stupid questions
Averaging color:
Here is what I get, sadly the resize to project (fit) doesn’t work. I have to make the dimensions explicit.
Hmm, how to explain this. Lets say I have setup an interior scene with mixed lighting, balanced for neutral (lights are what they are). Blue sky appears blue and yellow tungsten appears yellow. Now I want to use comp to create a slider where I can shift color balance, towards outdoor lighting (blue sky becomes whiter), or towards indoor lighting (yellow tungsten becomes whiter). I basically want to choose my virtual camera’s white balance setting, ending up with weird colors if I choose something stupid.
You could also do that with the above mentioned techniques, or you could just use regular color correcting. Try the Color Balance node, play around with it. Try a Hue Saturation node and shift the Hue value very slight increments at a time. That’s probably what you’re looking for.
