Painting Highlights: The Size of Specular Reflections

When we look at a portrait, figure or any object we seek to paint we are faced with a variety of highlights (specular reflections*) big and small, hard edged and soft edged. The shape of the form that reflects the highlight determines the orientation of its patterns (I hope to cover this aspect in an upcoming post) while the size is determined by the size of the convexity (or concavity--although I will only be presenting diagrams of convexities) and size of the light source.In figure 1 you can see how the size of the light source determines the degrees of a convexity that reflect the highlight at the angle of incidence = angle of reflection. If you imagine a point on one end of the light source and its geometry to the viewer, then the opposite point and its geometry to the viewer and the gradation of points between with their respective angles to the viewer you end up with the highlight's size according to the size of the light source. This establishes a constant we can rely on in any given scene: a viewer from a point in space will see a set of specular reflection in a set parameter of degrees.
So, why do we have highlights of different size throughout the figure when clearly the size of the light source remains constant?

This is answered in figure 2. Here we can see three convex forms (as depicted by the three circles inside each other) that are reflecting a highlight in the same range of degrees. The size of the highlight zone grows in proportion to the scale of the convex form.
One of the most obvious examples of this in everyday life would be the type of reflections you encounter on a vinyl record (figure 3). Each little groove has a tiny side that makes up convexities of progressively smaller sizes. The highlight pattern that emerges looks much like the range of degrees illustrated in figure 2.



UPDATE: Some of you may recognize that I've removed a portion of this post (some of the above diagrams will now seem a bit out of context, but may still have worth). This is because I need to rethink aspects of what I posted concerning the intensity of highlights. I don't want to put misleading information out there so I will revisit the topic in the near future with everything sorted out. In the way that teaching has been helpful in forming my concepts over the years it seems that blogging may be useful in the same way. I write something as I've discussed it and in rereading it I become more particular about the language I use and its implications. I hope to remain this vigilant about the information I offer and perhaps this demonstrates my desire to find the truth behind our visual experience.

I would appreciate any and all feedback.

*note* I will interchangeably use "highlight" and "specular reflection" to refer to the same phenomenon. Highlight is more convenient when talking about the net visual effect and is therefore good artist language. Specular reflection refers more to the parts of the highlight that produce the properties associated with highlights. Pure specular reflection would be found in a perfect mirror where there would be no absorption or diffusion to dilute it's effect.

New Portrait Painting

Here is a new portrait painting. I thought I'd put a few progress shots with it. Originally I wanted to put the entire drawing process up with this but after reviewing the pictures I decided otherwise--they were a bit blown out and skewed. I will be better next time and take scans of the drawings. So this begins after the transfer, tone and reinforced lines (with raw umber paint). The painting is "14 x 11"

Douglas Flynt's New Blog

I wanted to make sure everyone was aware of Doug Flynt's new blog. His most recent post, "The Anatomy of Light on Form" is an excellent presentation of the many ideas that have shaped my approach to interpreting and painting form. Check it out: http://douglasflynt.blogspot.com/

Interpreting Form: Diffuse Transmission

In this blog I will occasionally talk about some of the conceptual models I find useful when trying to understand the form I am painting. This week I thought I'd address a common phenomenon in translucent forms known as diffuse transmission. In diffuse transmission, light enters into an inhomogeneous surface, breaks down by continually loosing parts of the spectrum to increasing odds of absorption and exits with what visually appears as higher chroma and a shifted hue*, yet darker values than the reflected side of the object**. This can be contrasted with specular transmission where the visible spectrum does not suffer absorption in any measure and exits intact though possibly refracted.

*Let's say that a light emits photons with probability waves of Red, Orange, Green and Blue towards a surface. The surface is composed of atoms with 60% of the electrons having a frequency matching Green, 30% matching Blue, 10% matching Orange and none matching Red. At the surface a bunch of Red and Orange photons would diffusely reflect causing what would appear as an Orange-Red local. The saturation of this local would be neutralized slightly by the smaller percentage of Green and Blue photons who, despite having higher odds for absorption, still diffusely reflect at a smaller percentage across the surface. Light that enters the surface can scatter under the surface (a topic better left for another post) or transmit through. The odds of Green making it far into the surface without finding an absorption match is incredibly small, Blue may make it a little farther with Orange coming in second place to Red which transmits through with greater purity. This would leave us with a slight hue shift from Orange-Red on the diffusely reflected surface to something closer to Red on the Diffusely Transmitted side. Since there are fewer photons transmitting than reflecting, the value remains darker on the shadow side. (Keep in mind, the parts of the spectrum I'm using to describe this are just variables to illustrate the logic of this phenomenon and aren't specifically related to their various wavelengths and how they travel through different densities and distances--more topics for later posts)

**It should be noted that the values on the shadow side would be lighter when transmission is taking place than when it is not. This would be a logical conclusion (more photons=lighter value) in addition to being visually obvious. Above, I wanted to point out that with transmission the value gets darker with the chroma going up to contrast it with the chroma model I use on the diffusely reflected side where value and chroma go up proportionally as the form rolls towards the light (essentially seeing more of the object and therefore more of its local).

Two last things I'd like to point out: The computer generated diagram was made by me in Photoshop. It is a little unsteady and isn't the most solid demonstration of this activity. Maybe one day I will get 3D software and be able to build more consistent depictions of this stuff. Lastly, I'd like to add that I'm obviously not a physicist and other than actively reading about this stuff and discussing it with friends I'm unqualified to make absolute statements about what is happening on an atomic level. These models are the most consistent predictors for what I see daily as I paint and so far offer the most thorough explanation for Hue, Value Chroma shifts in form. I always want to get better and am always open to evolving and improving them. If by chance a physicist or anyone that finds fault in my thinking reads this, please leave a comment and publicly admonish me.

Additional Drawing Study for Painting

Just thought I'd add this to the drawings from this week's post. Because my figure drawings aren't very large I sometimes like to do a separate study of the portrait. This one goes to the figure posted below. I should point out as well that these aren't necessarily finished drawings...they are done to the point I need for beginning a painting. I hope to post short block-in demo videos in the near future that show how I develop these.

You know you're in trouble when...

...your town is mentioned on the national news: record breaking rain and flooding, including my studio. Fortunately I was able to frantically ferry out all of my paintings and most valuables. It could have been a lot worse so despite losing a week of work to cleaning up I'm grateful for not losing more. It's a shame that I wasn't currently working on one of my whaling paintings or I could have passed the whole thing off as an elaborate setup.

Mild disaster aside, here are a couple drawings that were done for some of the paintings currently rotating on my easel.