Blending displays seamlessly with the Edge Blending module [⭐ Pro]

⭐ This article revolves around a Pro feature.

In "Configuring an advanced projection setup with multiple displays", you've learned how to arrange the Output Setup in HeavyM in order to send areas of the Canvas to different display destinations.

In the use case we presented (two 1920x1080 projectors), the setup could end there if both projectors are meant to project on completely different spaces or side by side but with a gap between them. If you intend to use multiple projectors in order to expand your projection area, you'll need to use the Edge Blending module in addition.

What's the use of Edge Blending?

In reality, it's virtually impossible to combine precisely two projection areas side by side and make them seem like a single huge one seamlessly just with warping adjustments and no overlap or gap.

That's why, instead of trying to place the projection areas side by side, it's better to actually voluntarily make them overlap a bit and then apply some blending transformations to correct the appearance of the overlap strip.

These corrections are necessary, otherwise the overlap will be very visible, as you can see below:

Using the Edge Blending module

Let's use our previous case of two 1920x1080 projectors for this. Here, we want to set up both horizontally to create a wide projection area.

Before we start to configure HeavyM, remember that for a successful edge blending, the first thing you’ll need to do is to align your projectors physically as best as possible, one to the other. Of course, we'll see that you can correct small misalignments with HeavyM. But if your projectors are not aligned properly by hand, it’ll be hard to get a seamless edge-blending.

Let's move on to HeavyM now. Since multiprojection has already been covered in another article, we'll go over the basic steps rapidly.

1. Choose the Setup Output mode with or Output → Setup....
2. In a simple multiprojection case, our canvas size would be (1920+1920)x1080. But since we're going to make our areas overlap horizontally, we're gonna "lose" some pixels on the width.
   Let's say our overlap is on 400px this time, that makes our canvas size 3440x1080.
   
3. Add a second screen via the + button and snap it to the right side of the test card, so that the canvas is fully covered and the screens overlap by 400px.
   
4. Launch the fullscreen projection for each screen by selecting it and assigning it a Destination output.
   
5. Now, you should see something like this on your projection surface (I mean the real life projection this time):
   
   Note: at this step, if your projectors are not exactly placed side by side with the perfect overlap and you see on the test card that both areas don't fit perfectly, you should use the Warping options in HeavyM to correct the geometry of the outputs until you reach a matching rectangular shape.
   
   Assuming your outputs now create a perfect 3440x1080 rectangular projection area, there's one last thing to correct: the appearance of the overlap strip. To do so, we’re going to adjust the blending of each screen one by one:
   • a. Select the left screen in the Screens space and toggle its “Soft Edge” parameter ON from the Edge Blending section
   • b. Enter the width of the Right strip as previously decided: 400px
     (Note: prior to version 2.13, the width is calculated automatically based on overlap.)
   • c. Repeat these steps for the right screen (this time setting up its Left strip)
     
     Note: it's also possible to set the width of a screen's blending strip using the "Auto width" button. In this case, HeavyM checks the overlap of the selected screen in regard to other screens and enters automatically calculated values (which would also have given us 400px on Left/Right here.)
     This can be useful when you don’t have a precise pixel blending value and/or your blending takes place on several dimensions at once: no need to calculate or enter values one by one!
6. That should already be better! But it probably won't be perfect enough, so it's up to you to alternate between each screen by adjusting the perceived brightness of the fade areas with the Gamma Correction parameter and gradient smoothing with the Smooth parameter, until the overlap band disappears and two projection areas merge perfectly.
   
7. That's it! Just remember to uncheck the "Show test card" option (top right-hand corner) to reveal the canvas, then click "Ok" to save your configuration and exit the settings window.

Note: from HeavyM 2.13 onwards, it is possible to activate blending for an individual screen, without it needing to be superimposed on another. This enables blending between 2 projectors connected to different computers, screens don't have to be set up in the same space!