Soft-edge

• Principle
• Step-by-step
• Matrix Soft-edge

Principle

Soft-edge (sometimes called edge blending) allows you to create 1 continuous image with 2 (or more) video projectors.
 To do so, you can use a computer with multiple video outputs, or an expansion car such as Datapath X4.

The principle is simple. The 2 video projectors overlaps a bit, so they blend together :

Step-by-step

Here is a recipe to create a soft-edge :

• First, put all your projectors with a neutral keystone to maximise the projection surface.
   
• Place your projectors.
   They might be side by side with an overlapping surface of more or less 5/10% of the global surface. Here we took 40 pixels. What you see here is the black light of the projectors, the best their contrast will be, the less the black light will be visible.
   Keep in mind that soft-edge will not remove that black light.
  

• Configure outputs
   In Millumin, open the Output panel, then set a 2 x 1 layout as this example is a horizontal soft-edge (1 x 2 would be vertical).
   Then adjust the resolution. All the projectors must be at the same resolution. In that example, we have two 800x600 projectors which result in a 1600x600 canvas. Enter the resolution for one projector (800x600) in the field.
  

• Adjust the soft-edge
   This should be approximately the number of pixels that are overlapping. Here 40 pixels.

• Adjust the corner
   Click on Display test card, then adjust the mapping of both outputs so the circles and lines of the test-card are perfectly matching.
   Before :
  

  After :

• Adjust the color
   Open the color panel of the best projector (the one that have the wither image) and degrade it to have the same color on each projectors.
  

• Adjust the smoothness
   Now, going back to dashboard, you can use that continuous screen as a normal screen.
   If you see a white area in soft-edge, adjust the smoothness of the soft edge (if too high, this area will be brighter than the rest of the image).
  

Alternatively (and depending on your configuration), you could align the output corners first, then adjust the number of pixels overlapping.

Matrix Soft-edge

The same guide applies to more complex soft-edge, with a 2x2 layout for example.

Keep in mind that some edges will be shared by more than two projectors, so adjusting the mapping for each output takes more time. A good practice is to choose one projector, and adjust the other regarding this one.