Reflectance Characteristics of Graphics Objects
Specular and Diffuse Reflection
You can specify the reflectance characteristics of patch and surface objects and thereby affect the way they look when lights are applied to the scene. It is likely you will adjust these characteristics in combination to produce particular results.
Also see the
material command for a convenient
way to produce certain lighting effects.
Ambient light is a directionless light that shines uniformly on all objects in the
scene. Ambient light is visible only when there are light objects in the axes. There
are two properties that control ambient light —
AmbientLightColor is an axes property that sets the color,
AmbientStrength is a property of patch and surface objects
that determines the intensity of the ambient light on the particular object.
This illustration shows three different ambient light colors at various intensities. The sphere is red and there is a white light object present.
The green [0 1 0] ambient light does not affect the scene because there is no red component in green light. However, the color defined by the RGB values [.5 0 1] does have a red component, so it contributes to the light on the sphere (but less than the white [1 1 1] ambient light).
The size of the specular highlight spot depends on the value of the patch and surface object's
SpecularExponent property. Typical values for this property
range from 1 to 500, with normal objects having values in the range 5 to 20.
Specular Color Reflectance
The color of the specularly reflected light can range from a combination
of the color of the object and the color of the light source to the color of the
light source only. The patch and surface
property controls this color. This illustration shows a red sphere illuminated by a
white light. The values of the
SpecularColorReflectance property range from 0
(object and light color) to 1 (light color).
Back Face Lighting
The default value for
reverselit. This setting reverses the direction of the vertex normals that face away from the camera, causing the interior
surface to reflect light towards the camera. Setting
lighting on faces with normals that point away from the camera.
You can also use
BackFaceLighting to remove edge effects for
closed objects. These effects occur when
BackFaceLighting is set
reverselit and pixels along the edge of a closed object are
lit as if their vertex normals faced the camera. This produces an improperly lit
pixel because the pixel is visible but is really facing away from the camera.
Positioning Lights in Data Space
This example creates a sphere and a cube and illuminates then with two light sources. The light objects are located at infinity, but in the directions specified by their position vectors.
% Create a sphere sphere(36); axis([-3 3 -3 3 -3 3]) hold on % Create a cube fac = [1 2 3 4;2 6 7 3;4 3 7 8;1 5 8 4;1 2 6 5;5 6 7 8]; vert = [1 1 1;1 2 1;2 2 1;2 1 1;1 1 2;1 2 2;2 2 2;2 1 2]; patch('faces',fac,'vertices',vert,'FaceColor','y'); % Add lights light('Position',[1 3 2]); light('Position',[-3 -1 3]); hold off
light functions define two light objects located at
infinity in the direction specified by the
These vectors are defined in axes coordinates [x,