Diving Straight into Photographic Rendering

7 min read

(For more resources related to this topic, see here.)

Lighting that sets the mood!

While a good composition gives us a solid foundation on which to build a photographic render, if we try to render a scene that has no lighting, well let’s just say the end results will fall quite a way short of those desired.

The brilliant thing about lighting a scene with V-Ray in SketchUp is that a complete day-lighting system that consists of both the Sun and Sky elements is, by default, set up and ready to render with as soon as we start creating geometry in the scene. For newer users, this can obviously help tremendously when it comes to getting up and running with the software.

Controlling the placement of the Sun is extremely easy as we simply need to make use of SketchUp’s built-in shadow controls, wherein we set the month of the year along with the time of day and time zone, and then we can render. What we instantly get is natural-looking daylight without having to do anything at all!

Better still is the fact that V-Ray also sets up a basic indirect (or global) illumination system for us automatically. This means we can even render interior Arch Viz shots right out of the box without having to do any extra set up work beyond, of course, getting our geometry created and then positioned in the scene.

Global illumination is a general name for a group of algorithms used in 3D computer graphics that are meant to add more realistic lighting to 3D scenes. Such algorithms take into account not only the light which comes directly from a light source (direct illumination), but also subsequent cases in which light rays from the same source are reflected by other surfaces in the scene, reflective as well as non-reflective (indirect illumination). The source of this content is Wikipedia.

To look at the kind of renders we can get from V-Ray without doing any real lighting setup at all, either continue to work with your current scene or open up the Ch01_03_Lighting.skp file from your Exercise_Files folder, if you prefer to work with the same scene as I will be using.

Stepping through the render process

The scene or camera angle we are using here (Scene 2) has been deliberately chosen to help us properly evaluate the quality and level of lighting that we are getting in our scene. It can do this because it affords us a full view of the environment.

With our camera view set to Scene 2, let’s take a render by clicking the render button on the V-Ray toolbar. Once the initial translation phase is complete, V-Ray opens up its own frame buffer window and starts the rendering phase.

One of the very nice features of V-Ray Version 2.0 is the fact that translation times in scenes are now significantly faster (in the vast majority of cases) than rendering the same scene in V-Ray Version 1.49.

The first activity we see in the frame buffer window will be V-Ray’s indirect illumination calculations. First of all, the light cache and then the irradiance mapping engines calculate the level of illumination and light bounce requirements for the scene. This is based on the parameters set up in the V-Ray option editor and the materials applied through the materials editor.

Irradiance mapping and light cache are the two indirect illumination engines set up by default in V-Ray Version 2.0 for SketchUp.

The final part of this process is the rendering of the image itself. In this instance, what we get, as we no doubt could discern from the GI calculations, is way too dark for the type of bright and airy feel in the interior that we are looking for. This brings us to a critical aspect of lighting in V-Ray, exposure!

Using V-Ray’s physical camera model

Another default aspect of the V-Ray setup in SketchUp is that it makes use of a physical camera model for rendering. This means that real-world parameters such as shutter speed, F numbers (or F stops), and ISO (or film speed) values are used to control various aspects of the render, such as exposure, motion blur, and depth of field.

Basically, if we understand how to control these elements on a real-world camera, be it film or digital, then we already have a big head start when it comes to rendering using the V-Ray physical camera model. To access the physical camera controls, we need to revisit the V-Ray toolbar and click on the option editor button once more.

Then, if we open the Camera rollout, you can see in the following screenshot that we now have access to a wealth of camera controls and parameters. As we have already noted that our render is quite a bit darker than desired, the controls we are interested in would be those capable of affecting the exposure levels, which would be as follows:

  • Shutter Speed
  • F Number
  • Film Speed (ISO)

As a general rule, I prefer to handle exposure levels using only the film speed value as much as I possibly can. This is due to the fact that it is the only one of the three controls in what is often referred to as the exposure triangle that isn’t used to control some other aspect of the physical camera model. Shutter speed is also used to control motion blur while the F number (or F stop) value will typically be the control mechanism for any Depth of Field (DOF) effects in our render.

To get some nice brightness levels in this instance, let’s adjust the film speed or ISO value and set it to 1200. Taking another render by hitting the render button on the far right of the V-Ray frame buffer’s top toolbar will show us that our illumination levels are now much more appropriate for the bright, airy feel we want to create.

The higher the ISO number we use in a render, the more sensitive V-Ray becomes to light, thereby producing a brighter final image. Unlike the ISO setting on a digital camera, we can increase this value as much as we like in V-Ray without the fear of introducing artifacts or noise into our rendered images.

Global illumination controls

The next aspect of our lighting setup that needs a little attention is the quality of the indirect illumination solution. At this moment, we can see quite a bit of dark splotching on our nice clean geometry. This often happens when we work with scenes that present a little bit of a challenge to the indirect illumination engines, which, of course, interiors nearly always do. Couple this with the reasonably low-quality default settings that V-Ray sets up, and we get splotches or noise patches in our render.

To clean this up a little, let’s perform the following steps:

  1. Jump into the Irradiance map rollout in the option editor, and in the Basic Parameters section, set the minimum and maximum rate values to -2 and -1 respectively.
  2. We can also increase the HSph.subdivs value to 125 and the Interp.samples value to 35.
  3. Next, we can jump into the Light cache rollout and increase the Subdivs (or subdivisions) value to 1200.

If we take another render by hitting the button on the toolbar, we should see a marked improvement in the level of splotchiness present in the image; not that every trace of it will be gone, mind you. When working with interior scenes, creating completely noise-free Global Illumination (GI) renders can prove to be quite costly in terms of the time it takes to render the final image.

What we often have to aim for then is a situation that would generally be considered free enough of noise to be called an acceptable final solution. One reason why we can often get away with this is the fact that once materials get applied to the geometry, any slight levels of splotchiness still found in the scene tend to oftentimes just blend into the materials themselves.

We do need to bear in mind that every increase in quality settings inside a render engine, such as those we have just applied to the indirect illumination controls, will result in a corresponding increase in the time it takes for the render to complete! This is typically referred to as the speed verses quality conundrum.


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