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# Post Process Volume Color Temp is Backwards???

Definitely great to have white balance and color temp in the post process volume. This is a photographic standard. Except that color temp refers to the Kelvin CT scale. 6500 (default) is roughly white, while higher values are supposed to be blue (hotter) and lower values are red (cooler). Yes, blue is much hotter than red.

This model with red hotter than blue is a misperception of kelvin CT. It should be according to photographic standards. Can we use real Kelvin? Or at least have an option to switch to kelvin for those trained in lighting, photography and cinematography?

What makes it even more confusing is that it uses the Kelvin temperature range, implying that it’s Kelvin when it’s not. ie the color temp of a candle is around 1800 KCT. But if you set this value to 1800, you get blue.

LOR

When referring to the actual kelvin temperature, yeah the input is backwards. However, it’s meant to be used as the necessary temperature for a neutral balance, meaning if your surface is reading a temperature of 4500, then you set that as the temp. There’s no native solution to know what temp/tint is needed though, so it is a little unintuitive. Calculating the CCT isn’t too complicated though, if you wanted to go down that route.

Shameless plug, but I have a BP for calculating the CCT as well as a post-process material to visualize saturation here https://gumroad.com/l/oThQm There are numerous equations for calculating the CCT and none of them are 100% perfect(and will all give strange results if the source color is not around the Planckian locus), but between that and the saturation visualizer, it’s better than nothing.

OIC, this is a colour correct control. That makes more sense. Thanks @rosegoldslugs
I just watched a tutorial in which the artist used it as a global lighting colour control, which of course you could do by correcting in the wrong direction. It makes sense now.

lor

As an old photographer/videographer that’s just started to get into UE4 for archviz, I was rather stumped by how Epic deals with color temp in their lighting scenarios. I can only find in the UE4 docs where they rely solely on the PostProcessVolume color temperature/tint sliders to manipulate color temperature. Setting color temp in video is the single most important beginning step and attempting to do so in post is a kludge or disjointed results.

Also, the sliders only work globally and most any natural scene (not talking about games) in the real world has a vast variation of color temp. I’ve done numerous color temp tests over the last few years using Sekonic C-800, Lumu, Illuminati, and xRite iOne spectros that are placed in various parts of a shot and then recorded from sunrise to sunset. It’s amazing how much variation there is based on the time, date, cloud cover, scene type such as open field, buildings (inside/outside), shady woods, etc. Light reflections from a tangent can vastly alter a scene gray reference such that you can never truly get a neutralized white balance on the reference.

Anyway, I’ve been scouring the web researching this aspect of UE4 lighting and have found little discussion on it. So far, this thread is the only one that leads down the road I’m on, that of using reference sources to white balance UE4 lighting. I’ve already written RGB to Kelvin kludges which are semi-useful but only in ‘perfect’ scenes. I’ve experimented with the included colorchecker models in engine content and am working on a process that will allow sampling a neutral reference and adjust the temp/tint values accordingly and getting the neutral reference to balance.

LOR (first post), check out this link as to why color temp seems backwards. Adobe and other RAW conversion softwares has been doing this for years and very few people ever noticed.
https://www.wildlifeinpixels.net/blo…r-temperature/

Any feedback on this color temp scenario would be greatly appreciated from an old guy wore out from searching useless internet posts. ;0)

Also, in reference to rosegoldslugs BP for calc’ing CCT, why don’t you post it on the marketplace? Both videos referenced at your link get an ‘Error loading media: File could not be played’.
Thanx,
ZM

@ZM9019999 You’re right, it’s pretty cludgy. The general method in 3d for getting global colour temp right is post cc. Mainly because most virtual cameras are feature deficient (or just wrong). I am aware of some render engines where the developer of the camera code is not a photographer and doesn’t understand why shutter speed would or should control exposure. In film VFX ,the current standard is to have an individual “exposure” control on each light source, which you can see is totally strange, if you are a photographer. There are many uninformed and legacy ideas going into the tools. Properly trained photographers need to get in there and help them learn the well-established language and technology of photography.

lor

Excellent points and all true. As a master photographer (40+ years shooting commercially) I struggle with real world lighting control in Daz Studio, Blender, iClone and in the past Vue Infinite. Color temperature is not a global value but has been treated that way for years in all 2D/3D apps I’ve used. Maybe in UE5 these issues will be addressed, who knows.

Of note, the lights can be coloured with KCT if you enable Use Temperature, and it is correct. For cinematographers, IMO there should also be a CTO/CTB dropdown menu.