USAGE: sphere [-d diameter] [-c color] [-b bgcolor] [-t theta] [-p phi] [-l lambertian] [-s specular] [-e exponent] [infile] soutfile
USAGE: sphere [-h or -help]

-d .... diameter ......... desired diameter of sphere; integer>0; default=128;
.......................... determines the width and height of the output image
-c .... color ............ desired sphere color;
.......................... Any valid IM color is allowed; default=red
-b .... bgcolor .......... background color outside sphere;
.......................... Any valid IM color is allowed; default=black
-t .... theta ............ white light azimuth angle measure counter clockwise
.......................... around the sphere from the positive x axis;
.......................... 0<=float<=360; default=135 (lighting from the northwest)
-p .... phi .............. white light altitude angle measured downward from
.......................... zenith (i.e. from out of center of sphere toward viewer);
.......................... 0<=float<=180; 0 is light source right over the center
.......................... of the sphere; default=50
-l .... lambertian ....... lambertian (diffuse) illumination amplitude; 0<=float<=1;
.......................... default=0.9
-s .... specular ......... specular illumination amplitude; 0<=float<=1;
.......................... default=0.6
-e .... exponent ......... specular lighting exponent; float>0

If infile is provided, then it will be used in place of the color. The
infile must be square and the diameter will obtained from the dimensions
of the image.

PURPOSE: To create a colored sphere with a combination of diffuse and specular illumination.

DESCRIPTION: SPHERE creates a colored sphere with a combination of diffuse and specular illumination. Lighting is from a white light source. The diffuse term is computed from the Lambertian shading model. The specular term is computed from the Blinn-Phong approximation.

ARGUMENTS:

-d diameter ... DIAMETER of the sphere. Also controls the width and height of the output image. Values are integers>0. The default=128

-c color ... COLOR is the desired color for the sphere. The default=red. Any valid IM color is allowed.
See http://imagemagick.org/script/color.php

-b bgcolor ... BGCOLOR is the background color around the outside of the sphere. The default=black. Any valid IM color is allowed.
See http://imagemagick.org/script/color.php See http://imagemagick.org/script/color.php

-t theta ... THETA is the white light azimuth angle measured counter clockwise from the positive x axis. Values are floats between 0 and 360 degrees. The default=135, which means the light is coming from the northwest.

-p phi ... PHI is the white light altitude angle measure downward from zenith (vertical) towards horizontal. Values are floats between 0 and 180 degrees. A value of zero means the light is from above the sphere. The default=50.

-l lambertian ... LAMBERTIAN is the amplitude of the diffuse lighting. Values are in the range 0<=float<=1. The default=0.9

-s specular ... SPECULAR is the amplitude of the specular lighting. Values are in the range 0<=float<=1. The default=0.6. A value of zero means not to compute the specular component.

-e exponent ... EXPONENT is the specular exponent, which controls the area of the reflective effect. Larger values means smaller areas. Values are floats>0. The default=70.

NOTE: If infile is provided, then it will be used in place of the color. The infile must be square and the diameter will obtained from the dimensions of the image.

REQUIRMENTS: IM 6.5.4-3 or higher due to the use of -compose mathematics.

THEORY: See the following: http://en.wikipedia.org/wiki/Lambertian_reflectance
http://en.wikipedia.org/wiki/Blinn–Phong_shading_model

NOTE: This script may be a little slow due to the use in part of -fx.

CAVEAT: No guarantee that this script will work on all platforms, nor that trapping of inconsistent parameters is complete and foolproof. Use At Your Own Risk.