2 January 2009

Rendering an exterior at night in 5 simple steps, using vray

In this tutorial I will go through all the steps that we usually do when I’m asked to do an “exterior night-rendering”.
In order to follow it you need to know the basics of 3ds max and vray.

1) Natural light
The first step is to choose a background image of a sky.
For this tutorial I have used the image bellow:

background

Now put the desired image into the environment slot (3d max’s environment slot, not in vray’s).
In the vray settings, check global illumination, select lightcache for secondary bounces, irradiance map for primary (you could also use brute force, but it will take longer to render).
In the global switches tab, make sure that “default lights” is unchecked.

Last but not least go to the vray environment slot and check “GI environment (skylight) override. In the slot right beside put a gradient (dark blue in the upper slot, a lighter blue in the middle and a pale orange or purple in the lower position)

Exterior Rendering Settings

If you hit render, you will end up with something like this:

Exterior Rendering Phase1

2) Adding artificial lights inside
As you notice, it is starting too look like a night rendering, but at the moment it lacks artificial lighting so the spaces look deserted.

We will begin by adding vray lights inside the house, to simulate artificial lighting.
The important thing to keep in mind at this point is that artificial light can look different from one case to another depending on many factors (intensity, color temperature, size of the space that is actually lit, etc.) so you shouldn’t put a light source and instance it all over the place. Be creative and play with parameters like intensity multipliers, filter colors, etc.
For this scene I have used spherical vray lights with intensity multipliers varying from 1 to 2, filter colors with orange, yellow and blue tints and different a radius for each one.
vray interior lights

If you hit another render you will end up with something very similar to the following.
Exterior Rendering Phase 2

3) Simulating artificial light “spreading” from inside
Now we have light inside the house, but the light doesn’t seem to “come out” enough. Therefore we will place vray planar lights just in front of the windows, pointing towards the exterior, like in the following image.

vray window lights

Hit another test rendering and you should have something similar to the render bellow:

Exterior Rendering Phase 3

4) Adding artificial lights in the courtyard
We are getting closer. What doesn’t look right at the moment is the fact that the courtyard is too dark. Depending on your scene, you may have exterior lighting fixtures (like the lighting posts that I have in this scene), or even exterior spotlights that illuminate the building. If you don’t have specific instructions for these, you could place lights somewhere behind the camera, so that you give the impression that the space is receiving illumination from neighboring sources (street lights, car lights, or even other buildings).

In this particular scene, adding lights to the lighting small garden lighting posts should be enough.
First I have assigned them a vraylight material with a gradient map; than I have placed vray spherical lights over each one. For each vray light in the courtyard I have excluded the lighting post bellow it. This is kind of a fake, but in the end it looks right, and that’s all that matters. (If you want to do it more “accurate” check out the lampshade tutorial as well).

vray courtyard lights

Hitting a test render at this stage you should obtain something like this:

Exterior Rendering Phase 4

5) Photoshop touches
a) Add a subtle glow effect to the visible artificial light sources (in this case, the small lighting posts). You can do this using the diffuse glow filter.
b) In a new layer, add a linear gradient from bottom to somewhere at the middle from orange to transparent. Put the layer on “color” and play with the transparency until you like the result. If you are feeling creative, you can also try some subtle brush strokes, with different tints of red, yellow or orange to create diversity.
After having done all of the above, here is the final image.

(CLICK THE IMAGE TO VIEW A HIGH RESOLUTION RENDERING)

Exterior Rendering Phase 5

Conclusion
Rendering an exterior at night can be very tricky. The best approach in my opinion is to take it systematically by starting with natural light, and adding artificial lights one by one during the process. Otherwise, you may find yourself lost not knowing where you did something wrong.
I can not stress enough how important is to have a few examples of professional architectural photography at hand and look at them at every stage of the process.
Here are some general guidelines that I always keep in mind when I’m doing a night rendering:

1) Even at night time the skylight still casts a subtle shadow.
2) Never make the sky 100% black; it should have either a blue or a purple tint.
3) If there are no artificial lights on the ground, the sky will always be brighter and the ground would “borrow” a bluish or purple tint from the sky
4) The lighting is a mixture of dark purple/bluish tints at the upper part and orange/yellow on the ground and on the building(s). That is because the natural light blends with artificial light sources placed on the ground.
5) The colors are more saturated in a night rendering that in a daytime one.
6) Artificial light sources have a subtle glow around them.
7) If you have “moving objects” in your scene, don’t be afraid to use motion blur. If you know a bit about photography, you are aware that at night time photographers use high exposure times when they target architectural subjects; this causes all moving things around (cars, people, etc) to appear with motion blur.

If you think that I have missed something, feel free to post a comment and let me know.

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