[PT] Lighting the inside of dense forest

Started by WAS, November 06, 2020, 12:30:28 AM

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I've seen this as a suggestion in many renders, that the inner foliage is too dark, and I'm suffering the same issue. How can I remedy this when GI surface isn't responding with just the sun in PT? Especially when altering translucency of the foliage severely impacts look? In some instances I'm having almost near total blackness I couldn't even work with in post.


The only things I can think of are exposure, an extra no shadow sun high up (which is not 'natural' of course), more clouds (which would also be a 'hack', as there are not always clouds), and reducing leaf opacity to something above 50%.


Opacity may actually be the trick (assuming PT handles it relatively the same), I didn't even think of that and used it all the time, such as macro moss shots where a translucent flowing spore thingy may not produce a jet black shadow. Thanks for that!


Since it's not yet possible to increase the environment light with the path tracer (you can do it of course, but it has no effect), and Matt wasn't very excited about such a feature, since it's not physically correct, there's no other way but using hacks. Personally I don't like the idea of using no shadow suns, since it produces a very flat lighting to my taste, and encreasing the exposure would be the most correct way, but it makes everything brighter.
So my suggestion is using a very large white selfilluminated plane set to invisible and with "cast shadows" turned off above the scene. You can control the effect by modifying the luminosity strength. I don't know if this works for a dense forest, but at least it takes some shadowing into account, which makes it look a bit more real than adding lightsources without shadows. Maybe in combination with a reduced opacity of the leaves.


Wouldn't a second sun with very soft shadows work? You can probably use a low number of soft shadow samples in this scene.


I would first try to increase the soft clipping to about 2 and then increase the exposure. See what happens  ;D

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I have seen suggestions of using a reflective surface behind the camera much like in "real" photography but I have not been able to get this to work.
This may be down to my impatience ...

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How dense is the canopy; are there any open spots where the light enters? That would appear to be essential to illuminate the vegetation. If there are indeed open spots in the canopy you could increase the strength of the sun until you have the desired illumination.


WAS this may not be the effect you are looking for, and this may even sound an idiotic suggestion, but can you use an axial spotlight projected through the camera? I've no experience of using the spotlight in Terragen but I've used axial lights in real-world situations to lift the shadows without affecting highlights. The reason this technique works is that the highlights are many, many multiples of luminance above the level required to raise the brightness of forest depth, so a little extra light on highlights has no affect, whereas the shadows will respond to low levels of brightness. By the way, the image you post is very 'photographic' in feel because film was never capable of rendering the dynamic-range of digital.


Thanks a lot David. This has turned out to be a really informative thread. A lot of wonderful methods and info here.


@richard: an invisible card works fine to illuminate. I used it in my medieval 'Jack the Ripper' render for a bit of reflection on the dark side. Just grey of white will do as well as reflective.


Maybe you already tried this; I set the sunlight to 25 and the enviro to 0.6. The result is of course that everything outside the forest is overexposed, so it works best when the camera is completely under the foliage.
I think this is indeed a situation that traditional photography wouldn't be able to handle well on a sunny day.
This is a standard render; I do not know how Path Tracing handles this. ::)


In the Atmosphere shader, change the settings of the Haze density and the Bluesky density to 0.25. Anything else relating to overexposure that is not vegetation can be changed using a Surface layer shader (lowering the Apply colour setting), perhaps the Colour adjust shader and possibly other shaders that could be useful.