Gouraud Shading Vs Phong Shading

Gouraud Shading	Phong Shading
This method is also known as interpolation shading or color interpolation shading method.	This method is also known as normal vector interpolation shading.
This method was introduced by Henri Gouraud in 1971.	This method was introduced by Phong Bui Tuong in 1973.
It calculates the intensity at each vertex of polygon.	It calculates the average limit normal vector at each vertex of polygon.
It interpolates intensity over the surface of the polygon.	It interpolates the vertex normal over the surface of the polygon.
The problem of mach bands is more.	The problem of mach bands is less.
Example- Consider a figure where colour of point P inside the triangle is found by bilinear interpolation. Here scan line containing P intersects two edges at points P' and P". We first calculate the intensity at three vertices P1, P2, P3. We interpolate the colour of P1 and P2 to get the colour of P' we then interpolate the colour of P2 and P3 to get the colour of P". Finally, we interpolate the colour of P' and P" to get the colour of P.	Example- Consider a figure where we find the normal vector N at point P in a triangle, we first interpolate N1 and N2 to get N', then interpolate N2 and N3 to N" and finally interpolate N' and N" to get N.