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VRay for Rhino Manual
Sun and SkyThe V-Ray Sun and Sky are based off
of research to accurately depict the sun and sky, which allows for easy
recreation of the Sun and Sky. They are intended to work together as well as
react to the angle and direction of the sun. Add to add a V-Ray sun type
Sunlight into the command line. This will bring up the Sun Angle Calculator.
This will allow you to input time, day, and location. Once you've set your
desired parameters, click Okay and it will ask for an insertion point. Any place
is fine for the sun, so don't worry too much about where you put it. With the
light selected open up the light properties and you will see all of the
parameters for the V-Ray sun.
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Using the Sun
with the V-Ray Physical Camera In order to properly use
the sun, it is a necessity that it be used in conjunction with the
Physical Camera. The Sun itself is extremely bright, and in order to
maintain the characteristics of the model, the sun must be kept close to
its correct intensity. To counteract the intense brightness of the sun
it is important to create a proper exposure of a scene with the physical
camera. Using the physical camera will also help accurately capture the
correct colors of the sky as well.
Accessing the Sun Properties
You can access the properties of the sun by selecting it then
selecting Light under object properties. Here you will find many
different controls which change the appearance and affect of the sun.
For right now we will maintain the default value.
Exposing Your
Scene with the Physical Camera
Since the best way to make use of the Sun is to also use the physical
camera, access the V-Ray Options and in the Camera rollout enable the
Physical Camera. To determine the correct exposure you will need to do a
quick render of the image. If your image is too bright, or overexposed,
then you will need to adjust the F-stop, shutter speed, or ISO value to
compensate. It maybe helpful to view the color values in Float format,
as this will help you determine the true brightness of your image. This
can be viewed by right-clicking and holding anywhere in the frame
buffer. |
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The image below was rendered using the V-Ray Sun and the Physical Camera.
This image used the following values to achieve the correct exposure: F-Stop=
16, Shutter Speed= 200, ISO= 200.
| If you do not want to use the physical
camera it will be necessary to decrease the intensity of the sun by a
significant amount, however, the sun and sky may not act in the way it
was designed. |
Adding the
V-Ray Sky
Previously we were simply dealing with the only the V-Ray Sun, but now lets
go ahead and add the V-Ray sky. In the environment rollout of the V-Ray options,
click on the "m" next to GI parameters. You must have Indirect Illumination
enabled to access this, so enable it if you have not already. Clicking the "m"
should bring up the texture editor, and under Type select Sky. At the top you
will notice the option to select a light source. Click on that button and select
the light that was created via the sunlight command. Now V-Ray knows where the
sun direction is coming from, and this is an important step for having the Sun
and the Sky working together. Lastly, there is an option next to the button that
says Override Sun's Parameters. This allows separate settings for the Sun and
the Sky, but for simplicity and continuity it is recommended to have this
unchecked. Now go ahead and repeat this process for the background. If we render
again we'll notice that our white ground plane has a slightly blue hue to it.
This is due to the influence of the sky on our scene.
Time of Day and the Sun’s
appearance
Now that we have added the sun and sky, let’s see how the sun reacts to
changing the time of day. In order to change the position of the sun, select the
sun and go to the light properties. At the top of the window is a button named
Modify. Click on the button and it will bring up the Sunlight window and you can
change the position. Now the appearance of the scene has completely changed sole
based on the position of our sun. This allows users the flexibility to worry
only about the time of day rather than adjusting the appearance and intensity of
the sun and the background.
Changing the Sun’s
Appearance with Turbidity
Although the time and position of the sun will have the most affect on the
appearance of the Sun and Sky, there are several other controls that will be
helpful in adjusting their appearance. Turbidity essentially changes the amount
of dust that is in the air. Values on the lower end or the spectrum will create
a very clear blue sky as you would see in the country side. Having larger values
will make the sky slightly yellow or orangish as you would see in the city.
Think of turbidity almost as a control for the haziness of the sky.
Changing the Sun’s Appearance
with Ozone
The other useful parameter in adjusting the sun is Ozone. Ozone changes the
color of the sun itself from a slightly yellow tone to a slightly blue tone.
This can be very useful for fine adjustments to the appearance of the sun.
Gamma Correction and the
V-Ray Sun and Sky
Due to the physical nature of the sun and sky model it is intended to be
rendered using a gamma corrected linear workflow. Gamma correction compensates
for a monitor’s tendency to display mid-tones darker than they actually are.
Most programs embed the correction for this into the image, but because of the
nature of how V-Ray processes color information it does not correct for this.
Ultimately the result is that the VRay Sky will appear too dark if it is not
corrected for display on our monitors. Also if the image is not gamma corrected
the influence of the sky will not be accurate either. Needless to say, gamma
correction is very important, extremely so when using the V-Ray Sun and Sky.
The image below has no gamma correction. This causes the sky to be dark and
its colors to be inaccurate. The second image below has been gamma corrected,
which brightens the sky as well as having colors which accurately represent the
sky’s influence.
Enabling Gamma Correction
In order to gamma correct images both the inputs (textures and colors) and
output need to be adjusted. This is very quick and simple to do in the with
V-Ray as well as not impeding on workflow. In Global Switches, there is a
section in the bottom right corner containing the controls for gamma correction.
To adjust the inputs check Correct RGB and Correct LDR Textures. To adjust the
output change the Gamma value from 1 to 2.2
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