In my previous post I had noted that fresnel reflectivity was producing the most photorealstic results, however, before dissmissing other reflection types, I decided to conduct a further experiment.
In the renders below, the first image (top-left) shows three spheres rendered without any texture applied to them. It was interesting to note here that the spheres are very dark. When trying to achieve photorealism in this image previously I had noted that the spheres seem quite dark. Without any texture, it makes it far easier to see how dark they are. In the future this will prove useful when making adjustments to achieve correct exposure from the surrounding equirectangular panoramic HDRI sky dome.
In the second image (top-centre), adding some colour to the speheres supports the illusion of photorealism. This is perhaps because white is more reflective than black and some of the colours of the surrounding environment is seen to be reflected in the spheres. For example, there is a green tint in the bottom of the spheres where the surface of the filing cabinet is being reflected onto them.
In the third image (top-right), the spheres are 100% reflective. Contrary to my previous observations, this image does not appear as photorealistic as the white spheres. I believe this partly to be due to the reflection being too clean; in reality there might be smudges of grease, dirt and the like, you’d also be able to see a camera or similar in the reflection. In addition to this, the reflection in the coloured spheres is almost like a fresnel reflection which could account to its being more photorealistic.
However, this does confirm that fresnel reflectivity is superior, however, fresnel reflectivity alone is still flawed, as can be seen in the following image (bottom-left). In the image titled 100% Fresnel, the centre of the spheres has no reflection whatsoever. This is not a realistic effect.
It seems then, that it is a combination of all of these things that will have the greatest effect when trying to achieve photorealism in 3D renders, as can be seen in the final render.