Color attenuation in reflections - cell phone pic

Something’s been bugging me about reflections. It counts for eyeballs, car paint, etc in both Cycles and BI. It’s hard to put into words but I saw it last night when my girl friend sent me a cell phone picture of her dinner (left overs from our low country boil party this weekend). Because I don’t know the science behind it, I have to use laymen terms and simple words where Blender is filled with advanced terms, so maybe the smart ones can pick this torch up to make it happen.

Most everyone’s character’s eyes look like metal since eyeball reflections include a thorough scale of color. One post noted that after a distance, eyeballs (and car paint, etc.) reflect only the highest ranges of light. The result is more like a silhouette of what’s reflected rather than a mirror image.

More after the break…

This cell phone camera isn’t great, but it shows something I haven’t seen in Cycles or BI, the fast attenuation of color in reflections. The fresnel effect is immediately noticeable but then, even under even fluorescent lighting, that white plate suddenly pops up in the reflection like an island in black although the value of the marble counter is far above 18% gray - brighter than halfway between black and white.

The bright and colorful food does nothing more than reflect as a black shadow of itself. There’s even a lone kernel of corn about 1:00 o’clock on the plate that’s just a black speck on the reflection. If we were to recreate this scene, you’d want to know that a window pointing to the sunny late afternoon is about 3 and-a-half meters away; the brightest spots can be seen in the top-left third of the glass with trees silhouetted. The main light is one diffused source from overhead and some environment from the window.

The magic of this real scene presents a problem for me in texturing, modeling, etc in Cycles. The countertop stops reflecting though the glass clearly sticks that plate reflection right in plain view on a field of black. So fresnel alone would fail to answer this. I used FDRTools Advanced to run this through Tone Mapping software and can safely say that the camera recorded NO colors in that reflection for the food (overall range recorded at 15.6 units).

How can we fake this in Cycles and what are the scientific terms for this observation?

Are those reflections how it looked to your eye when viewing the scene - or is it an artifact cause by the lower dynamic range of the camera.

I guess you could simulate this effect by having a glossy node whose colour is controlled by a colour ramp going from white to a darker grey - controlling the transition between the two via the fresnel or layer weight node. Alternatively - mix two glossy nodes - one white one dark greay - again controlling the transition using the Fresnel and layer weight.

Might not be completely accurate but I think there’s nothing more going on than reflections, refractions, change in medium and differences in light energy.

In your image the glass has liquid in it, the surface is curved so that bottom parts reflect the table and top parts reflect the background with lights. Direct light has more energy than reflected light and more of it gets reflected back.

Some of the light gets reflected from the top surface, some of it goes through that surface and (with refraction) meets the glass-air barrier and again gets reflected back. This would mean that if you have a empty glass and look at the reflections that are not directly facing at you, you should see double image, or more like double edges with blurring.

Where the glass is filled, again some of the light gets reflected from the top surface but when it goes through the glass, it meets glass-liquid barrier. (Well it might be more accurately glass-air-liquid but let’s simplify). This time more light gets absorbed by the liquid and less of it gets directed back. If the light that hits it is already from a reflected source, it has less energy to begin with and less of it shows in the reflection, when compared to reflection of a direct light source.

The solution for reflection : (Light Path Node + Layer weight ) * fine tunning !!!

Those of us who paint are quite familiar with this phenomenon, e.g., reflections of boats in a lake must always look “darker” to be realistic. Since I am a relative cycles newbie, I wonder, oscurart, if you’d be willing to share more specific information about how to achieve this effect.

Hi Sabba if I understand your question you can do this accurately and easily by picking a reflection color that is darker and darker, but not changing the hue. In the example you give, the surface of the water should have a glossy color that is darkened (I prefer to do this by using the HSV picker and sliding the V). Now all the reflections will be dimmer, but just as sharp.
Many variations on this basic model of absorption of course are possible with using the layer weight node, and even more with the Light path node.