Blending with backdrops

The following tutorial shows how to set up using Image-based Lighting (IBL), blend shadows from your model with a backdrop, how to position the backdrop relative your model and adjust field of view.

We start with a SketchUp model of a Jeep.

We're going to light this model at 4cm intervals - choosing Resolution is about trading lighting time for fidelity typically you'd start with a lower Resolution while rigging, but this model will only take a minute or so in total, so we'll start with a higher Resolution.

We're using "Ambient Occlusion" with "IBL blend" selected. This means LightUp will use the backdrop as the source of light and ensure that the model blends naturally with the backdrop.

Further down, you can also see "Show Skybox" is checked. I've chosen a HDR backdrop of a field.

If you press the Tourtool button to start lighting, you should shortly get something like below.

Lets assign some material properties by clicking on materials and editing the realtime material properties. We'll edit the windscreen, wheel rims and body work materials.

Windscreen Material

Wheel rims Material

Body work Material

While material assignment improves the look, the Jeep looks like it is "floating in space" and makes no effect on the background; to solve this we're going to add a groundplane on which the vehicle can sit. Exit LightUp Tourtool by choosing a SketchUp tool or pressing Escape.

In order that the ground plane shows only the shadows cast on it, we'll mark it as a "Shadow Catcher". LightUp treats materials marked as "Shadow Catcher" differently during Tourtool and blends only the shadows and not the direct lighting falling on the surface.

Now when we start Tourtool again, we have a ground plane that captures the shadows of the Jeep and blends them with the backdrop. The Jeep no longer looks like it is floating in mid-air, but parked firmly on the ground.

Adjusting Backdrop and Field of View

The great thing about a realtime renderer is you can adjust things instantly without having to wait for another render to finish. The backdrop is fine, but I don't want to see that brick building in the background - I want to Pan the backdrop around to a better view. I can do this easily in Lightup, by holding down Ctrl on the backdrop and dragging the mouse left and right.

Better.. still need to pan around a little more.. Perfect

Lastly, we're going to tighten the field of view. Again we can do this all inside Tourtool by holding down Ctrl on the backdrop and dragging the mouse up and down. You'll see the current Field of View in degrees showing in the lower right corner of the window.

Our final image nicely blending with the backdrop using Image-based lighting"