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July 18, 2013

Posted on July 18, 2013 by Bill McKown, Synergis’ Visualization Expert:
I was standing out in front of our office the other day when something caught my eye moving on the sidewalk.  When realized it was just the breeze moving the shadows from the trees on the ground, it gave me the idea for this blog.
A very good technique for adding fake shadows in your 3ds Max scenes is by adding projector lights, or Gobo lights.  The idea of using Gobo lights is not new, it has been used in stage lighting for centuries.  It is simply something placed in between (Go between Optics) the light source and what you are trying to light with the sole purpose of casting shadows.  Why is this a good technique?  It’s cheap and easy (no geometry to model or extra rendering time). It is a nice way to project shadows on the ground from a tree canopy above or project complicated shadows to make our scene more interesting.  So we’re going to make a Gobo light of our tree canopy to project into our scene.
Examples of lighting gobos.


Here’s the imagegb4 I took of the tree shadows on the ground.
If you look closely at the shadows you’ll see the leaves that are closer to the ground are sharper, and the leaves that are higher up on the tree are blurrier.  This is because the closer the object is to the ground the darker and sharper the shadow is.

Inside 2"x6" compact florescent light 12" away

Inside 2″x6″ compact florescent light 12″ away


The further away from the ground the more light bounces and “wraps” around the object.  Look at the image of the Mr Incredible PEZ dispenser.  Notice the shadow getting blurrier and lighter toward the top of his head? The bigger the area of the light or the closer the light is to the object the more the light wraps around the object!

Setup:

I took some tree shadow photos into Photoshop, and increased the contrast, and adjusted the levels until they were nearly B&W.  I saved that as my tree opacity map (below left).  I also used the curves to increase the Greens in the photos and saved it out as my tree diffuse map (below right).
 

Tutorial:

Keep in mind there are several ways to use gobos.  You can assign a gobo as projectors inside of your light.  It’s under the Advanced Effects, Projector map (see below left).  Your light will then project the image based on the size of the lights falloff.
We are going to look at another method using cards with material applied to them in-between the light (see below right).  This method allows us to apply several different tree shadows to cards, and even animate them if we wanted to mimic a breeze.  Special thanks to Neil Blevins for sharing this technique, check out his website at Neilblevins.com.
  

Download the scene files: (Data files zipped here)

  1. Open a new 3ds Max file, or open the “Final gobo scene.max” file.
  2. Make a plane 10’ x 10’.  This will be our ground plane, so rename it “Ground Plane”.
  3. Open up the Render dialog box (F10).  Click on the Common tab to active it, and click on the Assign Render rollout and set the Production render to Mental Ray (see below).
  4. Make a few objects to place on the plane.  I used a cube, a cylinder and a teapot, but use whatever you want, we just need some objects to catch the shadows we’re going to project.
  5. Make another plane, 16′ x 12′ (roughly the aspect ratio of the tree photo I took).  Name it “Gobo plane”.  If you’re using your own tree shadow photos use a plane size roughly the same aspect ratio as your photo.  That way the image map will not be distorted when we map it to “fit” the plane.
  6. Create an Area Spot light, make sure you use Ray traced Shadows.  Position it away from your scene and make sure the falloff if wide enough to cover your entire scene. rename it “Sun”.
  7. Create a Skylight, make the multiplier =.5, and place anywhere in the scene (makes no difference where it is).
  8. Position your “Gobo Plane” in between your “Sun” light and your scene objects (like shown in Fig 2 above).  You will need to experiment by rendering and re-positioning until you’re satisfied with the shadow placement in your scene.
  9. Open the Material Editor, and create a new material using std material. 
  10. Click on the button that reads “None” next to the Diffuse Color slot.  Add the “Tree Shadows diffuse1.jpg” into this slot.  Drag copy this slot down into the Self-Illumination slot, and the Filter color slot (see below left).  * Adding the “Tree shadow diffuse1.jpg” to the Filter color slot will tint the shadows green.                                                                       
  11. Click on the button that reads “None” next to the Opacity slot.  Add the “Tree shadows opacity1.jpg”  into this slot (see above right).  Click on the Opacity rollout to open it.  Under the Coordinates rollout, uncheck “Use Real-World Scale”, and set the U and V Tiling = 1.0.  Also click the Output rollout and check the box next to “Invert” (see below left).  This reverses the image colors, what was black is now white.  Whatever is black in the image is transparent, whatever is white is opaque.                                                                                                  
  12. Create another Std Material, make it white color and name it “White”.  Assign it to the objects you created for the scene (Teapot, Cylinder, Cube, and Ground Plane).  You can assign it to those objects by selecting the objects in the scene and clicking on the “Assign Materials “button  (see above Right).
  13. Adjust the perspective, or create a new camera view  to set up a good view of your objects.
  14. Render the scene, and move your gobo until you like the resulting shadows.


And that is all it takes to complete this.  Leave a post or contact us if you have any questions.
Until next time, Render on…
Bill
Bill McKown is Synergis’ Visualization expert. Having joined the company in 2011, his prior employment involved CAD design, 3D renderings for both architectural and interior design projects, and training and supporting for all the products associate with these. Bill has a bachelor’s degree in Industrial Arts in Education and additional certifications in Computer Animation and Autodesk solutions.
See some of Bill’s other posts:

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