Perspective correct normal vectors for Phong shading

Linear shading interpolation is not physically correct in perspective projection. We present a perspective correct interpolation method. Our method achieves the perspective correct interpolation in the standard graphics pipeline in contrast to other´s that is calculated in a nonstandard graphics pipeline or by using similar triangles technology. We also show how to use this perspective interpolation to get the perspective correct normal vectors for applications such as Phong shading.