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## Description

This is 17th tutorial in my "Nsio Explains" series. I have frequently been asked for a shading tutorial, but for a long time I thought it's unnecessary. I didn't want to make a tutorial about something that's definitely covered in many other tutorials already in much greater detail. However, now I thought making this shading tutorial to explain why I find it's probably unnecessary to pay too much attention on this field.

Understanding 3D
I have few perspective tutorials in my series already, yet I keep returning to this point. As you may already know, I've based my artistic understanding on perspective and 3D. The first reason for doing that is that I wanted to be able to draw pretty much anything without relying on references. To do that I need to be able to draw objects that look three dimensional in all aspects.

My take on shading is mostly just a byproduct of extensive studies on perspective and 3D. Shading , in all simplicity, is just about adding shadow (or light depending on how you look at it) on 3D forms. All I need to do is to apply my understanding in a slightly different way, which ultimately is the same thing that I've been doing all the time.

That said, if you have problems with shading, then you most likely aren't familiar with perspective and 3D either. The thing is that your shading won't look convincing if you can't see direction in space. A common mistake is adding some shadows near edges without understanding how the light would really fall on the surface. Take a look at the example drawings: on the left, her arm casts a shadow on her shirt, making it look like her arm was touching the shirt. Or look how the skirt casts shadows on her legs, or how her legs are shaded. It looks just so blatantly flat that it's boring to look at.

Now the example on the right is exactly the same drawing but with some thought put on 3D. Can you feel the space between her arm and shirt? Can you see how her legs are in different orientation and thus the other leg is almost completely in shadows? This is where you should aim for, reproducing aspects that are so obvious it's almost ashaming.

When you understand 3D, shading skill in its basic form comes almost on its own, if we exclude the actual drawing techniques. Of course you need to practice shading, but it doesn't have to be your main goal.

1. The direction and nature of light source(s)
2. The orientation of the surfaces related to it (them)

There are obviously more advanced things when it comes to physics of light, but this tutorial focuses on just these two aspects.

Types of light sources

Let's start with the light that illuminates your objects. You are probably familiar with rays of light. In all simplicity, there are two types of light sources
1. Direct light (coming from a light source) and
2. Indirect light (light that derives from the light source but is coming from different direction)

Direct light is rather straightforward. Typically it's a point source which emits light in an arc or in all directions. Think a light bulb or a flashlight respectively. With point sources it's important to understand that the location of the light source has a big impact on the shadows. If the light source is very close, the shadows are huge and the further away you take it, the smaller the shadows will become.

When you go far enough, the rays of light that hit the object are nearly parallel. At this point you can simplify the light source as a planar source, which is like a plane that emits light in just one direction. This is typically a simplification of very large light sources or sources that are very far away. For example, the sun is a point source, but here on the Earth it behaves like a planar source. I typically treat the primary light source in my drawings as a planar source for the sake of simplicity.

Indirect light is special type of light which derive from the primary light source, but is reflected on other surfaces. When the light bounces from a surface, some of the wavelengths are absorbed and the color of the light changes. That's why very brightly colored surfaces "bleed" their color on other surfaces.

Most common indirect light source is the sky. The particles in sky refract the light so that there is some light even in shadows. Yup, there is light even on shadows. If there wasn't, all shadows would look black (like on moon which has no atmosphere that would refract light). In 3D rendering this is called global illumination. I'm not going into depth with indirect light here though. For now consider it just as a secondary light source.

Direction in 3D space

You see, you can simplify three dimensions into three axes XYZ that point in tree different directions and explain any other direction by using the XYZ coordinate system. As an example I have drawn four vector lines which look exactly the same, but their direction in 3D can be very different. This is the barrier that you need to beat, the conversion from 3D to 2D and back. Depending on the length of the primary vectors, the arrow points in different directions. Look at the black arrows at the bottom. They are projections on XY-plane of the four vector lines.

The four examples with cubes show how these four vector lines would cast shadows if they were indicating the direction of light. And that's pretty much it. It's just about understanding direction in 3D space.

Surface orientation

This is the direct derivative of direction in 3D space. Each point of the surface points in on direction. Depending on how the object is orientated in the space and how the light falls on it, it reflects different amounts of light. That's why a white surface may look gray instead. So even if some areas are under direct light, they reflect different amounts of light in your eyes. And when this light is weak enough or the object is in shadows, indirect light kicks in. Sky light is often pale blue, so shadows can have slightly bluish hue in them.

No matter how complex the shape is, it will follow the same rules. Sometimes the the object will illuminate itself as the light bounces on its own surface. I tend to simplify a lot, so rather than using the full range of values, I use only three (0%=white, 30%=light gray, 100%=black). This offers good impact/effort ratio.

Examples
Here I have drawn Youmu Konpaku from Touhou game as an example. Drawing this pose and viewing angle was really challenging and it turned out surprisingly well. As you can see, shading isn't necessary for attaining 3D look. In fact, your drawings should look three dimensional even without shading. Shadows will only make it look even more interesting.

In the next example I have drawn the direction of the primary light source as a blue arrow. This is my default direction of light in my practices. Note that even though the character basks in direct light, there is still plenty of dark shaded areas (like her left leg being completely in shadows). A good drawing should have a nice balance of light and shade in it.

If you change the direction of light even a little, it will cause major changes to the drawing. For example, now Youmu's face has more shadows.

Positioning the light source behind the character is a good challenge for shading practice. Basically you need to invert your way of thinking to bring up the forms that normally won't be seen in that way.

Light coming from below the character can have some pretty cool effect. In some cases it's for the best to focus just on accentuating the forms without following the light source too strictly. Maintain the balance at all times. It's art, it doesn't have to be right in order to look convincing.

Sometimes it's good not to go overboard with shading. As long as the forms don't look blatantly flat, applying basic shading isn't very demanding. It will make it easier for the viewer to look at the drawing as well.

Remember, the difficult part is understanding the orientation of the surface and direction in 3D space. If you master perspective, you likely don't need to practice this kind of shading at all. On the other hand, shading can be a good way to get into perspective as well, so it works in both direction.

I hope you find this at least remotely useful and interesting.
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