Part I: Adjusting the GI Settings
Step 1. First Render
1.1. Open the scene (which can be found here, size 36 MB).
1.2. Check the Override material option in the Global switches rollout.
1.3. Set the Image sampler type to Fixed Rate.
1.4. Go to the Output tab and set the resolution to 400 x 325.
1.5. In the Irradiance map rollout set the Min Rate to -5 and the Max Rate to -3.
1.6. In the Light Cache rollout set the subdivs to 500. We will change this to 1000 for the final render.
1.7. Render the scene:
Step 2. Tweaking the Exposure
2.1. Since the scene looks too dark, we would like to brighten it a bit. There are several ways to do this. One is to increase the power of the lights. However, this will make the directly lit areas of the image, like the patch of sunlight, too bright while indirectly lit regions will remain relatively dark. Other way is using the physical camera to adjust the overall exposure of the scene. This will also increase the brightness of the sun and some area could appear over-bright. Don't worry about that, because we are going to fix the burned areas using the color mapping.
2.2. In the Camera rollout, decrease the Shutter Speed to 40.
2.3. Other effect that we want to have is blurry shadows on the sun light. To achieve that effect we have to go to the Environment rollout and click on the "M" near GI(Skylight) and change the "size" to 30.
The result is quite noisy, but it does give a good idea of what the scene lighting is like. Notice that the sun is burning some areas in the render
Step 3: Tweaking the Color Mapping
3.1. By default V-Ray for Sketchup is using Linear as the color mapping. Therefore, we are getting very bright areas. In the Color mapping rollout change the color mapping type to "Reinhard".
You can see that the result is very close to the previous render with linear color mapping. The Reinhard color mapping is a blend between linear and exponential. If the burn value is 1.0, the result is linear color mapping, while if the Burn value is set to 0.0, the result is exponential style mapping.
3.3. The idea is to have an exponential style mapping. So, we have to reduce the Burn value to 0.3
The result is much better. We still have the same amount of light entering the scene, but we don't have the burned area produced by the physical sun.
At this point, the illumination is very good. The only issue here is the overall quality of the render.
Step 4. Better Antialiasing and Less Noise
In the first steps we change the quality of the render to be able to have a fast preview, while we are working with the illumination. Our goal now is to improve the setting to achieve better antialiasing, better GI and less noise in my render.
4.1. In the Image Sampler rollout, change the type to Adaptive DMC .
4.2. Set the Min Subdivs to 2 and the Max Subdivs to 6.
4.3. In the DMC Sampler rollout set the Noise Threshold to 0.008 .
4.4. The sun shadow has a lot of noise. To avoid that, we have to increase the subdivs of the sun light. In the Environment rollout, click on the "M" near GI(Skylight) and increase the subdivs to 32.
4.5. Render the scene.
Rendering takes more time now as V-Ray needs to calculate a more precise Antialiasing solution.
Step 5: Better GI Solution
The Antialiasing looks okay now, but we still have a low GI quality. For this reason we have some missing and blurry shadows. We'll deal with those now.
5.1. In the Irradiance Map rollout, set the Min Rate to -3 and the Max Rate to -1 .
5.2. Change the Color Threshold to 0.3 .
We do have better shadows definition, but we can see some splotches on the render. We'll adjust the HSph subdivs to improve that.
5.4. Set the HSph subdivs to 80.
Notice that the final render is noise free and the GI solution is very good.
This completes the first part of the tutorial. In the next part, we'll add the scene materials.
Part II: Rendering with Materials
Step 1. Rendering with Materials
1.1. Turn the Override material option in the Global switches rollout off.
The render looks pretty good with all of the material applied. It is time for the final render. We will render the image in a final resolution in the next part.
We now have to render the final image.
Step 1. Adjusting V-Ray for Larger Resolution
1.1. Set the resolution to 1600 x 1300.
1.2. In the System rollout, set the render region division size to 48 x 48.
We will need to adjust the irradiance map parameters: since we increased the resolution twice, we can decrease the irradiance map Min and Max rate by 2.
1.3. Set the irradiance map Min Rate to -6.
1.4. Set irradiance map Max Rate to -3.
1.5. In the Light Cache rollout, set the Subdivs to 1000.
Step 2. Rendering the Final Image
2.1. In the Output rollout enable "Save render output" to automatically save the rendered image. Pick the image file extension and assign a name and a path. For increased precision, you can choose a 16-bit image format (for example, a 16-bit .png).
2.2. Press the Render button.
The image looks okay, but in most cases you will want do some color correction in an image processing program.
For example, here is the same image some level, color balance and curves correction.
To add a more photographic feel to your image, you can apply some radial darkening of the corners and some chromatic aberration, for example like this: