Structured Light Lecture 1 Matt Waibel COMP 290

Structured Light Lecture 1 Matt Waibel COMP 290 -075 4 -17 -2000

Overview • • • Background General Setup Light Point Projection 2 D and 3 D Light Stripe Projection Static Light Pattern Projection – Binary Encoded Light Stripes – Segmenting Stripes • 3 D Photography on Your Desk

Background • Intersecting the projection ray with an additional ray or plane will lead to a unique reconstruction of the object point • Structured Light: projection of light patterns into a scene (active method)

General Setup • one camera • one light source – types • slide projector • laser – projection • spot • stripe • pattern

Light Spot Projection 2 D image plane

Light Spot Projection 2 D • Coordinates found by triangulation – b can be found by projection geometry – d = b*sin(a)/sin(a + b) – X 0 = d*cos(b) – Z 0 = h = d*sin(b)

Light Spot Projection 3 D Z

Light Spot Projection 3 D – X 0 = (tan(a)*b*x)/(f + x*tan(a)) – Y 0 = (tan(a)*b*y)/(f+x*tan(a)) – Z 0 = (tan(a)*b*f)/(f+x*tan(a))

Light Stripe Projection P

Static Light Pattern Projection

Static Light Pattern Projection • Project a pattern of stripes into the scene to reduce the total number of images required to reconstruct the scene • Problem: how to uniquely identify light stripes in the camera image when several are simultaneously projected into the scene

Binary Encoded Light Stripes • Set of light planes are projected into the scene • Individual light planes are indexed by an encoding scheme for the light patterns – Obtained images form a bit-plane stack – Bit-plane stack is used to uniquely address the light plane corresponding to every image point

Binary Encoded Light Stripes

Segmenting Stripes • Another Problem: How can we find the stripes in the images? • Thresholding is dependent on the contrast

Segmenting Stripes • Better Method: – Use the inverse image (opposite stripes) and determine where the intensities intersect with the original image

3 D Photography on Your Desk • Method that uses very common tools to do 3 D photography • Requirements: PC, camera, stick, lamp, and a checker board • Uses “weak structured light” approach

3 D Photography on Your Desk