How it works · Path A
Every Mirage performance is made of millions of tiny, soft blobs called Gaussian splats. Here's what a splat is, how millions of them add up to a picture, and how a computer learns them from ordinary photos.
Most 3D graphics are built from triangles: hard, flat surfaces stitched together into a mesh. A Gaussian splat works differently. It’s a soft, fuzzy oval that’s solid in the middle and fades out smoothly at the edges, like a spot of airbrushed paint.
The name comes from the Gaussian, the bell curve from statistics, which describes exactly how the blob fades. In a real scene, each splat is a 3D shape. On this page we draw them flat to keep things simple.
Each splat is described by just a few numbers:
Try each slider in the demo. Those few numbers are all a single splat needs.
One splat on its own is just a smudge. A full scene uses millions of them, overlapping in every direction. To turn them into an image, each pixel on your screen has to figure out which splats cover it and in what order.
This is called alpha blending, and it works a lot like stacking sheets of colored glass. The nearest splat contributes first, based on how solid it is. Whatever light gets through is shared with the splats behind it, and so on, until no light is left or you reach the background.
Because every splat is soft, the result doesn’t have the jagged edges you get with a mesh. That’s why splats are so good at hair, fabric, and skin.
Nobody places millions of splats by hand. They’re trained from photographs, using a simple loop:
The demo runs that same loop, live, on a small flat picture. A real capture does the same thing in 3D on a powerful graphics card, comparing against photos from every camera at once until the splats match all of them.
A good starting point helps. Random blobs work fine for a small picture, but for a real scene we first work out the rough 3D shape from the cameras, so training starts close to the answer.
Real things don’t look the same from every angle. A satin jacket shines from one side and looks flat from another, and skin has a soft glow along its edges. To capture that, a splat’s color can shift slightly depending on the direction you view it from.
Behind the scenes, this is stored as a small set of extra numbers on each splat (called spherical harmonics). You don’t need the math to see it, though. Drag the camera around and watch the same splat catch the light.