iOS11 ARKit: Can ARKit also capture the Texture of the user's face?

Question

I read the whole documentation on all ARKit classes up and down. I don't see any place that describes ability to actually get the user face's Texture.

ARFaceAnchor contains the ARFaceGeometry (topology and geometry comprised of vertices) and the BlendShapeLocation array (coordinates allowing manipulations of individual facial traits by manipulating geometric math on the user face's vertices).

But where can I get the actual Texture of the user's face. For example: the actual skin tone / color / texture, facial hair, other unique traits, such as scars or birth marks? Or is this not possible at all?

Answer 1

You want a texture-map-style image for the face? There’s no API that gets you exactly that, but all the information you need is there:

• ARFrame.capturedImage gets you the camera image.
• ARFaceGeometry gets you a 3D mesh of the face.
• ARAnchor and ARCamera together tell you where the face is in relation to the camera, and how the camera relates to the image pixels.

So it’s entirely possible to texture the face model using the current video frame image. For each vertex in the mesh...

1. Convert the vertex position from model space to camera space (use the anchor’s transform)
2. Multiply with the camera projection with that vector to get to normalized image coordinates
3. Divide by image width/height to get pixel coordinates

This gets you texture coordinates for each vertex, which you can then use to texture the mesh using the camera image. You could do this math either all at once to replace the texture coordinate buffer ARFaceGeometry provides, or do it in shader code on the GPU during rendering. (If you’re rendering using SceneKit / ARSCNView you can probably do this in a shader modifier for the geometry entry point.)

If instead you want to know for each pixel in the camera image what part of the face geometry it corresponds to, it’s a bit harder. You can’t just reverse the above math because you’re missing a depth value for each pixel... but if you don’t need to map every pixel, SceneKit hit testing is an easy way to get geometry for individual pixels.

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If what you’re actually asking for is landmark recognition — e.g. where in the camera image are the eyes, nose, beard, etc — there’s no API in ARKit for that. The Vision framework might help.

Answer 2

I've put together a demo iOS app that shows how to accomplish this. The demo captures a face texture map in realtime, applying it back to a ARSCNFaceGeometry to create a textured 3D model of the user's face.

Below you can see the realtime textured 3D face model in the top left, overlaid on top of the AR front facing camera view:

The demo works by rendering an ARSCNFaceGeometry, however instead of rendering it normally, you instead render it in texture space while continuing to use the original vertex positions to determine where to sample from in the captured pixel data.

Here are links to the relevant parts of the implementation:

• FaceTextureGenerator.swift — The main class for generating face textures. This sets up a Metal render pipeline to generate the texture.

• faceTexture.metal — The vertex and fragment shaders used to generate the face texture. These operate in texture space.

Almost all the work is done in a metal render pass, so it easily runs in realtime.

I've also put together some notes covering the limitations of the demo

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If you instead want a 2D image of the user's face, you can try doing the following:

• Render the transformed ARSCNFaceGeometry to a 1-bit buffer to create an image mask. Basically you just want places where the face model appears to be white, while everything else should be black.

• Apply the mask to the captured frame image.

This should give you an image with just the face (although you will likely need to crop the result)

Answer 3

You can calculate the texture coordinates as follows:

let geometry = faceAnchor.geometry
let vertices = geometry.vertices
let size = arFrame.camera.imageResolution
let camera = arFrame.camera

modelMatrix = faceAnchor.transform

let textureCoordinates = vertices.map { vertex -> vector_float2 in
    let vertex4 = vector_float4(vertex.x, vertex.y, vertex.z, 1)
    let world_vertex4 = simd_mul(modelMatrix!, vertex4)
    let world_vector3 = simd_float3(x: world_vertex4.x, y: world_vertex4.y, z: world_vertex4.z)
    let pt = camera.projectPoint(world_vector3,
        orientation: .portrait,
        viewportSize: CGSize(
            width: CGFloat(size.height),
            height: CGFloat(size.width)))
    let v = 1.0 - Float(pt.x) / Float(size.height)
    let u = Float(pt.y) / Float(size.width)
    return vector_float2(u, v)
}