Looking at Light: Value Keys

Last month we learned about the anatomy of a shadow and covered the six basic elements that make a convincing 3D form. To recap, let’s take a look at this image.

We can see that each of these forms is separated into a dark and light side. The transition between these two areas is marked by the terminator, which is labeled in red. Depending on the form, this transition will be sharp, as seen on the cube, or more gradual, like the other three forms. The terminator is the darkest part of the shadow side.

On the light side, we have midtones and highlights, marked in orange and turquoise, which help to illustrate the location of the light source as well as begin the transition toward the terminator. On the shadow side, we have a cast shadow, the edges of which originate from the terminator, as well as some reflected light, which bounces from the ground plane in the cast shadow up onto the form itself. Finally, we have the occlusion shadow, marked in yellow, which indicates where the form touches the ground plane.

Now that we know how to arrange the elements of our shadows and lights, let’s take a look at how to choose our values. The exact values we choose for our image will depend on a number of different factors. We’ll need to consider the type of material and its color, as well as the environment around it. Is it inside or outside? What’s the weather like? What time of day is it? These are all factors that will have an impact on our value structure. For now, let’s take a look at how the environment controls which values we can use.

The easiest way to do this is to find a reference image for the type of lighting and environment you’re aiming for. For this demonstration, let’s use this photo of a flock of sheep in a snow-covered field. Based on the lighting we can tell that it’s daytime, and because the sheep are pretty evenly lit and their cast shadows aren’t very sharp, we know that the lighting is pretty diffused. Another thing to take note of is the trees in the background. Possibly due to fog or the reflection of the snow, the atmospheric perspective is pretty heavy and we can just faintly make out their shapes. We can use this image to generate a value key which we can use in our own work to recreate the lighting conditions of this photo.

This image is split pretty evenly into two halves: the foreground and the background. Let’s start by sampling the darkest and lightest values in these two areas and comparing them to our value scale. I’ve placed them against a 50% grey background so we can better judge their values and lined them up with their corresponding position in the value scale. From this, we can see a couple of interesting things. First, despite this image clearly taking place in a field of snow, there isn’t any pure white present. Second, the darkest and lightest values found in the treeline in the distance are actually fairly close to each other on the value scale. Let’s put these to use and combine it with the shadow anatomy we learned last month.

Using the 2 value keys we sampled, I placed spheres into the foreground and background. Because they adhere to the values defined by the image, they don’t feel out of place. If you look closely, you can see that I have still incorporated the shadow elements that we learned previously. Next month, we’ll discuss how an object’s material and color affect its value. For the time being, try this out for yourself. Find some images with interesting lighting and see if you can add some basic forms using those same values.