
INTRODUCTION TO LASER SCANNING MICROSCOPY
LSM 510 Functions
B 40-051 e 07/98 5-59
Render - Surface: Method Description
This method displays the surface of structures in the Input sequence shaded as if a light illuminated it.
The position of the light is behind the view point with parallel rays in the direction of the sequence.
The input sequence is segmented into object and background by grey value thresholding: object voxels
are within the grey value range Grey Low to Grey High.
Each Output pixel corresponds to a point at the surface at which the ray in view direction through the
Output pixels hits the surface. All rays are parallel.
The surface normal required for shading in this gradient renderer is the grey value gradient in the Input
volume at the surface voxel position. It is not the geometric surface normal. The grey value gradient is
determined from the grey values in a 3x3x3 cube around the surface voxel by averaging e.g. the x-
gradient in y- and z-direction [4].
There is no depth cueing (far objects would appear darker).
The illumination model is a Phong model [1] (surface normal is determined for each Output pixel) with
diffuse reflection and specular reflection. Diffuse reflection means that the surface reflects light with
equal intensity in all directions. The brightness of a given surface patch depends not on the view-
direction, but only on the angle between light and surface normal. Specular reflection is observed on
shiny surfaces as a highlight. The light is reflected as from a mirror. The maximum intensity is observed
when the view direction is the one of the mirrored light direction.
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