VRay for Rhino Manual
Transparency mapping is another method using Bitmap to create materials. The
difference is that this is using alpha channel to get rid of unwanted part of
the Bitmap, saving only the part covered by alpha channel. This is called a
This is used mostly for creating product logos, stickers and numbers. Many
users try to avoid using transparency mapping and model the actual object in the
scene. Although you can ignore material settings by creating the actual model of
objects, that will increase both the number of objects in the scene and the file
size. The more objects you get, the longer the rendering time you would need.
You will get the result as left image if you apply the texture map directly
without transparency map. The black background of the texture map is blocking
part of the cup. The image on the right is rendered with transparency map.
Open Cup_Decals.3dm. Here is the object
and the transparency map that we will use to create our label.
You will get the result as the image below if you apply the texture map
directly without transparency map. The black background of the texture map is
blocking part of the cup. The second image below is rendered with transparency
1. Click on the cup and open its Material
Editor. Open Cup_Red; right click on Diffuse Layers to add a new layer and you
will have the dialog window as the second image below. A Diffuse1 control panel is
added under the Diffuse.
2. Click on the "m" at the right of
Transparency under Diffuse to enter the Texture Editor. Load the Bitmap for
Transparency texture map. Make sure you uncheck the Tile first to avoid
repeating this Bitmap on the object.
Use Photoshop, PhotoImpact and similar image editing software to create
black and white image and save as .bmp, .jpg or .png which are the formats
accepted by V-Ray.
3. Use Diffuse1 color to edit the color
for this Transparency map. Click on the "m" at the right of Color to add more
texture to this map if needed.
Render it and will get image like below. The Transparency map is covering the
entire cup. That's because there is no mapping applied to this cup yet.
4. Under Properties>Mapping, add a new
channel, change the projection type to Planar, and adjust the mapping widget's
size and position as image showed below. If the Tile remains checked, it will
render as the second image below.
How Transparency Mapping works
The diagram below depicts transparency mapping. The idea is using a grayscale
image as mask, black area will not be penetrated and only white area will let
light through, other gray area will then become translucent.
The white area get the color assigned in Diffuse1 and end up showing on the
surface of the object after rendered.
For the cup example above, after assign a mask to the Transparency, the red
color of the cup is affected by the white area of the mask and no longer showing
red. The second layer of the Diffuse1 color at the diagram below is used to
cover the white area of the first layer.
Another method for
creating the same result
Totally opposite from the method above, set the Diffuse to white,
Transparency as mask, but switch the black and white area, and let the Diffuse1
color show up at the upper layer. Assign the Diffuse1 color to red and will get
the same result as above after rendered.
Other Uses for transparency
There are many ways to use transparency map, not just used only for text mask
as example before. Here are some more examples often used to create a texture
map. First is using a gradient Bitmap as the Diffuse Transparency mask; let the
yellow color of Diffuse1 show up through the white area at the cup and create
two gradient colors on the cup as the second image below. This is the better way
then using a gradient Bitmap directly as the Diffuse texture because of its
flexibility of changing the colors. You will have to make another Bitmap of
different colors combination if the color need to be changed.
The second example is using other grayscale Bitmap as the transparency mask.
Although it is not a gradient image, but they work exact the same. A rendered
image is below.
The third example is adding another Diffuse2 layer, and assigns a 0 degree
and a 180 degree gradient Bitmaps to Diffuse and Diffuse1 in Transparency. Give
the Diffuse2 a third color to create this three-color gradient rendering effect
for the cup. A rendered image is below.
The forth example is to use gradient color in refractive material. Similar to
previous examples, use a gradient grayscale Bitmap as the Diffuse Transparency
mask. Add a Refraction layer to create the half transparent and half opaque
The fifth Example is the same as the third example, with the difference being
a refraction layer, and changing the transparency color of Diffuse2 to white.
This will make the white area at the middle become transparent. A rendered image
The example above can not have the transparent quality at the top and bottom
of the cup because of the black color in the grayscale gradient Bitmap. The last
example below is to use a pre-made gradient Bitmap as the Refraction
Transparency map. Set the Diffuse Transparency to a usual white, and then assign
the Bitmap to Refraction under Refraction control panel, and you will get the
same result as the second image shown below.