Raytracing - how to combine diffuse and specular color?

Question

I've been reading numerous articles about ray tracing and shading, but my ray traced image does not look too good. I'm talking about the very bright green area near the specular highlight. The result green color is maxed out here, it looks like. How to adjust colors and/or shading calculations to make this look correct?

(Never mind the silly code, I'm just trying to get the principles correct first).

Here's how it looks:

Here is the diffuse component only:

Here is the specular component only:

EDIT: Changing diffuse to Color diffuseColor = ColorMake(0.0f, 0.6f, 0.0f); Then the image looks like this:

Point lightPosition = PointMake(-100.0f, 100.0f, -100.0f);
Color diffuseColor  = ColorMake(0.0f, 1.0f, 0.0f);
Color specularColor = ColorMake(1.0f, 1.0f, 1.0f);
Color pixelColor    = ColorMake(0.0f, 0.0f, 0.0f);

//  Trace...

            // Diffuse
            Point intersectionPosition = PointMake(x, y, z);
            Vector intersectionNormal = VectorMake((x - xs) / rs, (y - ys) / rs, (z - zs) / rs);
            Vector intersectionNormalN = VectorNormalize(intersectionNormal);
            Vector lightVector          = VectorSubtract(lightPosition, intersectionPosition);
            VectorlightVectorN         = VectorNormalize(lightVector);
            float      cosTheta        = VectorDotProduct(intersectionNormalN, lightVectorN);
            if (cosTheta < 0.0f)
            {
                cosTheta = 0.0f;
            }

            pixelColor = ColorMultScalar(diffuseColor, cosTheta);

            // Specular
            Vector incomVector    = VectorSubtract(intersectionPosition, lightPosition);
            Vector incomVectorN   = VectorNormalize(incomVector);

            float myDot = - VectorDotProduct(incomVectorN, intersectionNormalN);
            float myLen = 2.0f * myDot;

            Vector tempNormal     = VectorMultScalar(intersectionNormalN, myLen);
            Vector reflectVector  = VectorAdd(tempNormal, incomVectorN);
            Vector reflectVectorN = VectorNormalize(reflectVector);

            float mySpec = MAX(-VectorDotProduct(reflectVectorN, incomVectorN), 0);
            mySpec       = powf(mySpec, 5);

            specularColor = ColorMultScalar(specularColor, mySpec);
            pixelColor    = ColorAdd(pixelColor, specularColor);
            pixelColor    = ColorClamp(pixelColor);

            [self putPixelatX:i andY:j andR:pixelColor.r andG:pixelColor.g andB:pixelColor.b];

Answer 1

This has long been an issue with the "specular + diffuse + ambient" model of illumination. Namely, it is a hack and therefore, has no guarantee of correctness.

If you're so keen on cementing your fundamentals first, take a look at the excellent book "Physically Based Ray Tracing" by Matt Pharr and Greg Humphreys.