Structured Light Lecture 1 Matt Waibel COMP

Overview Background General Setup Light Point Projection 2D and 3D Light Stripe Projection Static Light Pattern Projection –Binary Encoded Light Stripes –Segmenting Stripes 3D 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 2D image plane

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

Light Spot Projection 3D Z

–X 0 = (tan(  )*b*x)/(f + x*tan(  )) –Y 0 = (tan(  )*b*y)/(f+x*tan(  )) –Z 0 = (tan(  )*b*f)/(f+x*tan(  ))

Light Stripe Projection P

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

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

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

3D Photography on Your Desk