CMSC 491A/691A
Implementing Phong Specular Illumination

Spring 1999

Computer Science and Electrical Engineering Department
University of Maryland, Baltimore County

Phong Specular Illumination Formula for Intensity
(from 435 class notes, pg. 8-12)

da=I_ak_a + I_pk_d (N · L )
I=d_a + (1-d_a)I_pk_s (N · H)ⁿ
Add specular if N · L > 0 and N · H > 0

Object Color and Illumination

Now we need to add color into this intensity calculation. The diffuse and ambient intensity is multiplied by the color of the object. Specular illumination is affected by the color of the light, not the object in the simple model. (The color of the light actually affects all components.)

	n_l = (N · L)
	if (n_l > =0.0)
	   da = obj_amb[obj] + obj_kd[obj]*n_l
	else 
	   da = obj_amb[obj] 
	d_a.r = da*obj_color[obj].r
	d_a.g = da*obj_color[obj].g
	d_a.b = da*obj_color[obj].b
                   spec.r=spec.g=spec.b=0;
	if (n_l > 0)
	{
	   n_h = pow(MAX(0, (N · H)), obj_specexp[obj])
	   spec.r  = obj_ks[obj]*n_h
	   spec.g  = obj_ks[obj]*n_h
	   spec.b  = obj_ks[obj]*n_h
	}
	final_color.r = MIN(1.0, (d_a.r + (1-d_a.r)*spec.r))
	final_color.g = MIN(1.0, (d_a.g + (1-d_a.g)*spec.g))
	final_color.b = MIN(1.0, (d_a.b + (1-d_a.b)*spec.b))

Faceted Shading:

Create a structure to hold the user selected color of each object (obj_color[obj])
Create a structure to hold the final color after illumination of each polygon (face_color[obj][face] ) Set face_color[obj][face]= final_color.

Examples of illumination types

Ambient Illumination	Diffuse plus Ambient Illumination	Specular plus Diffuse plus Ambient Illumination

CMSC 491A/691A Implementing Phong Specular Illumination

Computer Science and Electrical Engineering Department University of Maryland, Baltimore County

Phong Specular Illumination Formula for Intensity (from 435 class notes, pg. 8-12)