Interior Lighting and Rendering Using Mental - 7th _ Dec

Chapter ? | Interior Lighting & Rendering using Mental Ray.

REFRENCE IMAGES

INTRODUCTIONWhile rendering our scene in 3ds max or any other 3d application, we first need to understand the

behavior of light. The interaction between the light and the subject is our main concern. In this chapter, we will be covering some of the Optical fundamentals and try to imitate those in our 3d application using Mental Ray rendering engine.

NOTE | Please go through the previous chapter “Product lighting and rendering using Mental Ray” before starting this topic for the details which is already been discussed and won’t be mentioned here.

“LIGHTING”

We usually keep all the geometries grey (mid luminance value) to do the lighting test. Which is also known as clay rendering. This is to get better understanding of highlight and shadow.

Below is the render of the scene with MR Area Light. We use area light in order to get feathered shadows, which usually happen in the evening.

Things to take care:

1. Direction of light: - It is our first priority to decide the direction of light and the altitude of light - how high is it from the horizon. And from which direction is it coming from? In above example, if sun light came from the opposite direction, we would not see the direct light because of the wall. So, these simple and minor things play a very important role. It can also be used for composition of the frame.

2. Color of light: - Another most important thing. Colors are often used to define the time and weather. It is also used to create the mood.

3. Intensity of light: - Intensity should also be take care in priority. It also helps us define time and weather.

With the combination of the direction, color and the intensity of light, we can roughly make people understand the time, the weather and the mood. We can sometime define the latitude too.

Enable the Global Illumination (GI) now.

NOTE | we have only used 1 directional light till now.

“Global Illumination” – Diffuse to Diffuse light bounce

When light (photon) collides with any surface, it further spawns more photons and travel in space. This process keeps on happening. This is known as “Bounce”. So when bounce happens, the newly generated photon takes some amount of the physical properties along with it such as the color, the intensity, and lot more. This again is transferred/pasted on the other surface when further hit. So the area which is not directly lit by the light is also lit indirectly with bounces. That’s why we see more bounces in surface whose color luminance is high. I.e. we get more light in the room with bright walls than that of dark walls.

“GI Photons” under light properties means the count of photons used to generate illumination by the particular light. Like: How many photons should the particular light throw. And “Energy” means the multiplier of the intensity of the GI Photons. Multiplier varies in proportion to the scale of the geometry. If the geometries are made too small, value should kept low and vice-versa.

Here, we can have a rough idea of the scale of our geometries according to the size of the grid.

Let’s increase the size by 400% keeping the photons count and energy value same. Below is the result

Hence, the energy proportionately depends on the scale of our geometries. Below is the visual Diagnostics of the photon maps that is being distributed by “bounce”. To view | go to Render Settings > Processing > Enable Diagnostics. Red color shows the highly affected area where the blue color has the least or no effect.

Indirect light diagnostics

Below is how the photon looks like. To control the photon size | go to Render Settings > Indirect Illumination > Global Illumination

By default, maximum sampling radius is off. That means its radius is 1/10th of the radius of the full scene. We can change the radius according to our need. In the above image, radius 5 is too small that is why we are seeing all those circular patches. So we need to increase the size. Or disable the maximum sampling radius to keep it 1/10th of the scene which gives useful result in most of the cases.“Cleaning Off”

Somehow we find those photon artifacts in our render even if we increase the maximum sampling radius and GI Photons. That is because of the shape of photon map which is hard on the edges. So we use “Final Gather” to clean it off by average all the points by further sampling its directions to get better result as shown below.

“Final Gather”

Use FG Precision Presets to set the final gather quality. Set it to “Draft” for test renders. Slide it to “Medium” or “High” for the final render. Changing the preset will increase/decrease the value of FG Density, Points and Interpolation which will directly affect the render time. Higher the values kept, higher the render time it takes.

Below is the graphical presentation of Final Gather points in action. To enable | go to Render Settings > Indirect Illumination > Processing > Diagnostics > Final Gather

Note | Diffuse Bounces will not work when Global Illumination turned on.

Let’s enable a skylight to get the environment light. We can also put HDRI image on it to get color information.

Note | Skylight will not work when Final Gather turned off.

We can add some Mr. Sky Portal Lights to give some light which is coming from outside windows.

Apply Textures to the geometries and render it again. But it is very important to calibrate our monitor and set our Gamma and LUT correctly to get the right colors in our renders and to get rid of the problems such as colors burnout out of over exposure, color fading out, color difference in various monitors and so on.

Note | after textures applied, light might not appear same. That happens due to irregular distribution of color luminance in maps that we use as our textures.

You might also want to add some extra lights on it. Like: tube lights, bulbs, etc. Below is the renders for such examples.

Note | It is recommended to model the scene in proper measurement as far as possible to get good result while using physically accurate lights (such as Photometric lights) and render engine.