Visual Reality: Tutorials: Carrara

Creating a Simple Facet Transmapped Leaf

You don't need to spend hours modeling the perfect leaf. In fact, unless you're doing a close-up image of just that one leaf, you shouldn't. For leaves on bushes or trees, a simple facet using transmapping will render faster and look just as realistic.

Preparing the Leaf Texture Map

To complete this tutorial, you will first need to scan a leaf. If you don't have a scanner, you can take a digital picture of a leaf. Be sure to photograph it laying flat on a solid white background. To use the image to create the leaf in Carrara, you first need to create transparency around the leaf portion.

1. Open the scanned leaf image in Photoshop or another 2D image editor.
2. Use the Magic Wand tool to select the white around the leaf.

   Note: Depending on the quality of the scan or photo, and on the shape and smoothness of the leaf's edges, you might need to use other selection tools to further select areas in the image that you don't want to appear in the final leaf object.

3. On the menu, click Edit, and then click Cut
4. On the Layers palette, delete the background layer so only the leaf layer is left.
5. The image should now have only the leaf, surrounded by transparency.
6. Click File on the menu, and then click Save As.
7. Browse to the directory where you want to save the file.
8. Type leafwtrans.png in the File Name field.
9. Select PNG from the Format list, and then click Save.

Creating the Facet Object

Next you need to create the facet object in Carrara.

1. Start Carrara and create a new scene.
2. Click Insert on the menu, and then click Vertex Object to insert a vertex object into the scene. Carrara will switch to the Vertex Modeling room so you can create the object.

   Note: You can also click the Insert Vertex Object icon directly above the workspace, and then click and drag in the workspace to create the vertex object. Or, if you click the Insert Vertex Object icon and drag it to the Scene line in the Instances tab on the Properties panel, it will create the vertex object in the exact three-dimensional center of the scene.

3. Click Construct on the Vertex Room menu. Point to Insert 3D, and then click Grid.

   

   Fig.1. The Insert Grid dialog



4. The Insert Grid dialog is displayed. (see Fig.1)
5. Type 5 in in the U size field.
6. Type 5 in in the V size field.
7. Type 2 in the U vertex count field.
8. Type 2 in the V vertex count field.

   Note: If you want to bend the leaf, set the U vertex count and V vertex count fields higher. The higher the values in the fields, the more facets the object will have, and the more smoothly it will bend.

   

   Fig.2. Click the Z arrow in the Perpendicular section to align the facet to the Z axis. You must click the actual arrow, not the letter Z.



9. Click the Z arrow on the Perpendicular icon. (See Fig. 2)
10. Click OK to create the object. If you specified a U-vertex and V-vertex count of 2, it will be created with a single facet. Otherwise, the number of facets will be determined by the number of vertices you specified in those fields.

UV Mapping the Facet Object

Before adding the texture and transparency map to the object, you need to UV map it. UV mapping tells Carrara which part of the object gets which part of the image applied to it.

1. In the Vertex Modeler, select all facets of the object.
2. Click the UV Map tab on the lower right-hand panel.

   

   Fig.3. The Carrara UV Editor when you first open it.



3. Click UV Editor. The Carrara UV editor will open. (See Fig. 3)
4. On the Edit tab, make sure Wrap U and Wrap V aren't selected.

   

   Fig.4. The UV Editor Projection tab. The Box Mode options, from left to right, are: Cover All, Cover Front/Back, and No Cover.



5. Click the Projection tab. (See Fig. 4)
6. Select Box from the drop-down list box. This will set the object's UV mapping to a simple box.

   Note: Different projections work better for different objects, based on the object's basic shape. Because the object in this tutorial is a flat, simple facet, either Box or Planar would work for it. Box is used in this tutorial because the Cover All option makes it easy to map a single facet to the UV map image. For a round shape, through, Spherical would be a better choice. Cylindrical would be the best choice for a tube.

7. Select Cover All for Box Mode.
8. Leave Framed unselected.
9. Click Apply to apply the UV mapping to the object. (See Fig. 5)

   

   Fig.5. The UV Editor Projection tab after applying Box mode with Cover All to the object.



10. Click OK to save the changes and return to the Vertex Modeler.

Creating the Leaf Shader

You can now create the Carrara shader for the facet object, using the leaf image and transparency in the leafwtrans.png file to render the facet object as a leaf.

1. Click the Assembly Room icon to return to the Assembly room.
2. Select the vertex object.
3. Click the Texture Room icon to switch to the texture room.

   

   Fig.6. The setup of the leaf texture in the Carrara Texture Room.



4. Select Texture Map in the Color channel. (See Fig. 6)
5. Click the Load button . The Open dialog is displayed.
6. Browse to the directory on your computer where you saved the leafwtrans.png file.
7. Select the leafwtrans.png file, and then click Open.

   

   Fig.7. The Choose File Format dialog.



8. The Choose File Format dialog is displayed. (See Fig. 7) Select PNG from the list, and then click OK. The image file is set for the texture's Color channel.
9. Make sure White is Invisible and Premultiplied Alpha are not selected.

   Note: If White is Invisible is selected, the non-leaf parts of the object will be black instead of invisible. If Premultiplied Alpha is selected, the leaf will have a jaggy white border around it.

Rendering the Leaf

With the leafwtrans.png texture map selected for the Color channel in the model's shader, it will now render as a simple leaf.

1. Click the Assembly Room icon to return to the Assembly room.
2. Adjust the facet so it's facing the camera.

   Example:

   • Object Rotation X: -0.33
   • Object Rotation Y: 41.55
   • Object Rotation Z: 34.78
   • Camera Center X: 7.97
   • Camera Center Y: 7.69
   • Camera Center Z: 14.18
   
   
3. Click the Render Room icon to switch to the Render room.
4. Select the Light through Trans. checkbox on the Rendering tab in the right-hand panel.

   Note: You need to activate Light through Trans. for shadows to work correctly. Otherwise, the object will cast a square shadow. By selecting Light through Trans., the object casts a shadow in the shape of a leaf.

5. Click the Render button to render the image. (See Fig. 8)

Fig.8. The rendered leaf in front of a plain gray sphere. The pullout in the upper left corner shows the unrendered scene with the simple facet object.

The same object can be used with different texture maps to create different leaves, flower petals, feathers, butterfly wings, or any other paper thin object. You can even change the object's size in the Assembly Room to accommodate objects that are wider or narrower. As long as you don't modify the object in the Vertex Modeller, you won't need to UV map it again.