By Andrzej Sykut

Web: https://azazel.carbonmade.com/

 

Follow Andrzej Sykut’s series on Lighting La Ruelle outdoor illumination with chapter 2: Sunrise/Sunset…

Before placing a single light in a 3d software, it’s good to spend a while, looking at the scene, and thinking, imagining a bit. The assignment is pretty clear – sunset/sunrise – that’s the ‘prime directive’. But that is not all that matters. Composition of the image is important, regardless of the lighting scenario we have to achieve – and that too can influence light placement, strength and color. Visual style, art direction is important as well – is it supposed to look real, photo real, stylized? Finding some reference can suggest few ideas, how to achieve our task. It’s also good to think about technical aspects – is it going to be a still image, or is it for animation, should it render really fast, or maybe we have some computing power at our disposal? But nowadays, when the computers are fast, it’s not always that important.

So how does all that theory work in real life case? Well, there are two most obvious (and easy to recognize) ways of showing a sunset. In the first one, the sun is behind the camera. The shadows of the buildings, especially off-screen ones, can become a very important element of the scene. Because there are parts of the image in warm sunlight, and some in the cooler shadows, there can be quite a lot of color variation (Fig.01), and the contrast isn’t very high. Second approach, we are looking at the sun – there’s a lot of bright light, things are shiny (because of the glancing angle of the sun rays), there are nice, long shadows, and the overall contrast can be quite high, but there can be little in a way of color variation (Fig.02). Both ways differ in mood quite a bit – of course, you can choose somewhere in between – it depends on the scene, and on the story you want to tell.

There are similarities, too. In both cases, sun is our main (key) light source. Sky acts as a fill – but the ratio between the two is different. This looks like a great candidate to use Vray Sun&Sky system as a base of our light setup, at least at first glance. While it should work for the first scenario, it may not be flexible enough for the second one – in that particular scene. The arch at the end of the street blocks the horizon, (Fig.03, marked red) and whole scene would be in shadow… unless we try something else.’

Let’s start with the first approach.

To render the scene, I’m using 3dsmax with Vray, with GI turned on. I most often use Irradiance Map for first bounce and Brute Force for the secondary bounces – that is the default setting, which works for me in most cases (Fig.04 – preview setting). Detailed settings, like number of bounces, or Irradiance Map size of course vary over time – low quality for previews, higher for final rendering. For still images, as in this case, I try to use fastest (lowest) setting possible, while still getting acceptable result. For animation, the Medium Animation setting is usually safe, flicker free option. I also use a hint of global Ambient Occlusion to add some detail to shadowed parts of the image.

Next thing I did was setting the Color Mapping to Exponential (Fig.05). While this isn’t probably the most physically correct way, it has some advantages. The way it works, it prevents overbright ‘hotspots’, and oversaturated color transitions. It’s also very tolerant – it’s really hard to whiteout the image, and the lights have a very wide range of usable multiplier/strength setting (but that range often ends up being pretty high, like 512 or so, especially with the fog on). It has downsides, too, making the colors look desaturated, and decreasing the contrast of the image. I actually like it that way, because I can easily bring back the contrast and saturation in post production, and for some scenes it just fits – but if you don’t like it, there’s HSV exponential mode, which keeps the colors better. Generally, though, main use I have for default, Linear Multiply, is rendering some additional passes, like masks.

Then, I’ve set up the road surface (Fig.06). A simple Vray material, VrayDisplacement modifier, and we are good to go. I also added some reflections to the windows (using blend material, VrayMtl for the windows, and a b&w mask). Metal parts, like railings and lamp also use shiny, reflective VrayMtl.

Now it’s time to create the sun. Let’s choose VraySun. The pop-up will appear, asking about adding VraySky in the Environment slot – I hit OK, since I’ll need it. Next I switched VraySky to manual sun node, and pointed the newly created VraySun as the sun node (Fig.07). To have a bit more control, I used two variants of the sky – one for lighting, using Vray’s environment override, and one to be visible. The difference is in the sun intensity multiplier.

To position the sun, it’s good to display shadows in the viewport (Fig.08). That way I can see the shadows in real-time, and finding a nice composition is really fast… but wait, there’s nothing that could cast shadows on our street. It’s easy to fix – just draw few skyline-shaped, angular splines, and extrude them a bit, then place roughly where the other side of the street would be, and tweak from there (Fig.09). Here I chose the to have a nice, lit path into the image, and dark shapes on both sides.

Before rendering anything, I created VRayPhysicalCamera, so I could control the brightness of the scene in more intuitive way (as I have a bit of photographic experience). The settings pictured on (Fig.10) took some trial and error to get them right – generally, if the scene is more-or less build in real world scale, the settings that would work if we were to take a photo of that scene in real life, are a good starting point. The Vignetting option is quite useful here, darkening the corners of the image, and focusing the viewers’ attention at the central part of the image. I also adjusted the sun brightness, and size, to get nice, soft shadows.

Let’s see what we’ve got (Fig.11). Not that bad, but could be better – I’d like some more blue in the shadows, and some more light in the central part of the image. I added a big blueish Vray Light above and to the front of the scene (Fig.12).

This gives more color variation, and, as it is, looks more like a sunrise, – but it’s easy to go back into sunset territory, with few tweaks in post-production. Another, smaller light further along the street (Fig.13) lights up the arch wall, which was bit too dark for my taste.

I’ve also added a small light behind the arch, so there’s no big flat dark spot in the center of the image (Fig.14).
Now, let’s take the image into Photoshop, and see what we can do with it. Using Curves Adjustment Layer, I brought down most of the blue/violet from the shadows, giving the whole image a warmer tone (Fig.15), played with vignetting, and some glows, and here’s the final result: (Fig.16). All in all, this wasn’t too hard, was it?

The second scenario is bit more tricky. Let’s start with the scene I’ve just finished, and remove all lights except the sun. If I set the sun where I want it, and render, the colors are all wrong – cold, blue, instead of war browns and oranges. Simply the sun is too high to have proper warm color (Fig.17).

If I swap the VraySun for the standard Directional Light, I can have full control of its color. I replaced the VraySky (the one doing the lighting, in Vray override tab) with a HDR photo of a sunset (To be honest, the scene would probably work even without it, as its effect is subtle, and most of the lighting will be done by hand. Still, it’s some starting point.), bumped up the Primary Bounces multiplier, played with AO settings, and Vray camera settings (Fig.18) – and the colors start to look right, but the scene is way too dark (Fig.19).

The walls of the street are in shade… as they probably should, but I’d like them to catch some light, so I put a squashed, spherical Vray Light under the arch (Fig.20). The right wall has a slightly reflective material (added as a Shellac to the base shader), so there is a nice detailed pattern there.

Another light was placed above the roof, to throw some back-light on the wall on the right (Fig.21).

Yet another, quite big one, placed above the street, simulates the light coming from the sky (Fig.22) – but it’s not enough, so there’s another, even bigger one above the camera, facing the scene, providing some fill light on the forward-facing parts (Fig.23). Using big area lights has some advantages – you can add light coming from certain direction, but without sharp shadows, which would clutter the image, and without a very characteristic in CG, point/spot light distribution, which is not always desired. Besides, it works like a big softbox/bounce in real world, either in photography studio, or on a movie set. The downside is rendertime, and sometimes noise, if the sampling of the shadows is not good enough.

Before final rendering, I tweaked the backlight above the roof a bit – less saturation, bit more intensity, and rotated it a bit – no big deal, really. There’s another problem here – a light bleeding in the corner. To fix that, I could use higher quality Irradiance Maps, or try to use Detail Enhancement – at the expense of rendertime – but as the image will be rendered in high resolution, the settings I have now, should be enough (at high resolutions, even the low Irradiance Map settings provide enough information to get a clean rendering). Actually, I’ve lowered them even more, but that required some slight fixing to be done.

What the scene lacks is some atmosphere – I left that for the very end, for the postproduction stage. I rendered a Zdepth pass, and added slight fog in Photoshop (Fig.24), along with some other simple tweaks. – and the final image looks like (Fig.25).

Seeing those two approaches, we can draw some conclusions. The automatic Sun/Sky system is a great starting point, and in some cases, it’s probably good enough by itself. But as good as it is, it is not always flexible enough, and some scenes will greatly benefit from few well placed additional lights – and some will have to be lit mostly by hand – which is not that hard, once you have a clear direction of what you want to achieve. And that’s where some research can be very helpful.