How to paint coherent local value ranges ?

6 minutes read —

Among the various light sources that could be set-up, direct sunlight is the one we should refer to when studying values. Contrary to spotlights, direct sunlight hits everywhere with the same intensity ; there is no drop-off. This means we have one less parameter to worry about.

We will refer to a value scale ranging from 0 to 10, with 0 being pitch black and 10 being pure white. Any color can be picked and sorted along that scale. Please refer to my previous post for accurately picking values in Photoshop or you might fall for measurement errors.

Any subject has what is called a local color, or base color. That color is only then altered by lights and shadows. To better understand, think of the local color as the color you would see if you lit your subject with a flat white light coming from everywhere. Or in more practical terms, this is the color you would pick if you painted flat colors.

Please note that any color has its own distinct local value before it is even altered by light. A yellow is noticeably brighter than a blue or a red. A brown is darker than an orange.
As a direct consequence, if you picked local colors of different objects in a scene, you would get values all over the place. There wouldn’t be much to think about ; there would only be random. It’s not that much of a stretch to conclude that local values just aren’t that important for an accurate rendition of lighting.

Yet we are able from values to perceive volumes. The reason this occurs is because planes of an object that are facing the light source then bounce that light back to our eyes. Planes of an object that aren’t facing the light source aren’t catching any light and thus remain in darkness. In fact, they would remain pitch black if we were on the moon. On earth though, the water in the air reflects some amount of light and acts as a secondary light source emitting in all directions. Even though such reflected lights are weaker than direct lights, they prevent pitch black from occurring. We could get lost in details here, but what I’m coming at in simple terms is that any object has a lightest value, and a darkest value.

Again, the lightest value would appear on the planes facing the light-source directly and the darkest values would appear on the planes that aren’t facing the light-source. There is a clear separation between the lit and unlit areas, that we lazily refer to as “the separator”. This difference between light and dark, is everything. Understanding values is not about absolute numbers, or how dark or light a specific color is. It is much more about how much darker or lighter that color is relative to the color next to it. It’s all relative.

The bigger the distance between the lightest and darkest value ; the harsher and hotter the light. Bigger value ranges are typically seen midday. Under weak lighting such as a cast day, the value
A distance of 5 between the lightest and darkest values of a given object is typical.

Now ; what is really interesting to notice, is that all objects that fall under a same sunlight, regardless of their local color, present the same distance between their lightest and darkest values on the value-scale. To demonstrate, let’s paint a couple of volumes next to each other and light them. Their local colors and values could hardly be more different. However, because they are under the same light, you can count on one thing to be true ; they will all present an equal distance between their lightest and darkest values. If I have a local blue sitting at 6 and going down to 1, then my yellow sitting at 9 will go down to 4 in its unlit area. As you would have understood by now, the important information is the value range that this lighting dictates. All sort of local values can be used, as long as the range between light and shadows is cohesive for all colors used in the scene. This is grammar. This is what ties a painting together and create a sense of light.

You might wonder though, what would happen in that 5 units differential scenario should I add a new ball with a local value of 3 ? Simple arithmetic tells us that the darkest value should then be minus 2, and surely we do not know how to paint a minus 2 value. Do not worry though, simply paint the area black in this case, and then add-in your bounce lights from there. What happened is that we simply didn’t have enough of a scale to be able to render all the information. This also happens the other way ; sometimes a lit object should get so bright as to appear in values above 10. In that case, the lightest values would simply cap at 10 and you would observe a flattening of the information above that mark. This is what we call respectively underexposure and overexposure. It can be used to great effect in painting as it can occasionally put some tasty emphasis on shapes and silhouettes in key areas.

By this point we’ve got ourselves a nice little rule, but it is still largely insufficient to paint a realistic painting. I can think of two additional clauses we should add.

The first one is that materials will have an influence on this value range I keep talking about. Indeed, the smoother the surface of a material is, the more light it is going to reflect and therefore an equally intense light source would be able to produce brighter values. As a consequence, reflective material such as metals usually present a much wider range than matte objects between their lightest and darkest values. Inversely, painting value ranges that are more compact can be used to signify materials that are particularly matte relative to other objects, such as skin.

The second caveat is atmospheric perspective. The air between your eyes and the objects you are painting is not empty. It is full of water and particle and they reflect light back to you. It is useful to think that for every unit of distance you are adding a semi-transparent sheet of colored paper between you and the object. What this does to values ; it squishes it towards the value of the sheet. Because this sheet is usually quite light, the local value tend to go up, and then the value range tend to reduce the more distance you travel. This means even under and even light that should create a 5 units differential between light and shadow, you will see distant object displaying a difference of only 2 units or even less.

I’ll make sure to discuss those caveats more extensively in later posts.