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#### 明暗处理 光线 以及物体

Shading Light and Form - Basics

Hey Welcome to Proko my name is Stan Prokopenko,

a lot of you have been asking for a video on

shading. The first thing you need to understand when starting to shade

is how light affects the appearance of form

and how to properly capture 3 dimensional form

based on the characteristics of the light in the scene.

In some of my previous videos I talked about things like shapes, values and edges.

But how do we know what shapes, values and edges to draw?

What exactly are we looking for?

Well, we’re looking at Light

and how it illuminates the objects in our picture.

Light is the reason we see anything and the

characteristics of light can completely change the appearance of the things it illuminates.

So, I like to analyze the light in the scene and try to

capture it, so the viewer can FEEL the light.

Form looking 3-dimensional is a byproduct of correctly capturing the light on the form.

Ok, so I hope I’ve convinced you that studying light on form is important.

Now let’s take a look at all the elements.

For this I’m gonna need an egg.

For this I’m gonna need an egg.

There are two main zones. Light and shadow.

The edge where the form transitions from light to shadow is the terminator.

It’s located at the tangent between the light source and

the form. In other words, just before the planes start to face away from the light.

There are two types of shadows.

from the light source. A cast shadow is caused by one form blocking the light from hitting

another form. This egg is blocking the light from reaching this part of the table. You

can find this shape by projecting lines from the light source to the termination of the

first form, and continuing those lines to the obstructed form.

Shadows will rarely be completely black.

Light bounces off objects in the environment and is reflected back into the shadows.

This is called reflected light.

In this case the light will bounce off the paper and into the shadowon the egg.

Along the terminator, sometimes you will see a core shadow.

It’s a darker plane that defines the edge of the shadow.

The thickness and softness of the core shadow can vary quite

a bit. It depends on the thickness of the form, how sharp the edge is between the planes

of light and dark, or the angle and position of the reflecting light source.

Sometimes you won’t see the core shadow at all.

Only if there is something on the shadow side, to reflect back enough light

to create a visible difference in value. This

dark piece of paper reflects less light than the white paper.

You can see a drastic difference in the value of the reflected light.

Also, regarding the visibility of a core shadow,

the reflection has to come from the right

angle. If it’s directly behind the shadow side,

it will create a nice core shadow. If

we move the reflection source closer to the angle of the main light source,

it will illuminate the area where the core shadow would have been.

If you don’t see a distinct core shadow, many artists choose to cheat one in because

it can add to the 3-dimensionality of the form.

Reflected light doesn’t just affect form shadows. It also affects cast shadows.

Less light can bounce into this deep crevice where the egg and table meet,

and so that area gets darker as it goes deeper. This is called an Occlusion shadow.

Moving on to the light zone, immediately after the terminator, is the halftone. These are

planes of the form that are partially hit by the direct light.

As the planes get closer and closer to facing the light, they will get lighter.

And the point where the form points directly at the light is called the center light.

The center light shouldn’t get confused with the highlight.

The difference between the two is that the center light is the plane facing the light source,

whereas the highlight is a reflection of the light source.

A reflection will move depending on where the viewer is.

So let’s say this is the egg.

The viewer, or camera is down here, and the light source is over here.

The center light will be here facing the light source. The highlight however

will need to be at the point where the light can bounce off the surface of the egg and

reach the viewer’s eyes. These two angles need to be equal.

If you’ve played billiards, this is very similar.

To test this concept let’s mark the point of the highlight,

and mark another point for the center light.

Now let’s move the camera and see what happens. Ok, you can see here

that the highlight moved to a different spot, following the camera. The center of light

hasn’t changed. It still pointing directly at the light source.

Don’t let the math of all this confuse you.

Highlights, and also cast shadows which we discussed earlier, can be changed

and they can still look believable.

Nobodys going to call you on a highlight being in the wrong spot.

I can take the highlight on this egg, move it to a different spot, and change the shape.

And it still looks believable…

I’ll often change the shape of a cast shadow

to better describe the form it is being cast

onto. For example if I have an object that casts a shadow appearing to go against the

form. The form of this paper towel roll is a cylinder and to show that I would change

the cast shadow from the egg to wrap around the cylinder.

I usually try to describe the form that the shadow is casting on to,

rather than the form casting the shadow.

So, give yourself artistic license. Learn the rules,

and then learn how you can break the rules to improve your drawing…

Just want to let you guys know, I will be releasing a DVD very soon.

It’s gonna have all the video tutorials I’ve done so far,

PLUS a few extras that will be available only on the dvd.

I’m hoping to have it available in the next few weeks.

And as always, if you liked this video,

share it with your friends. They might like it too.

And don’t forget to subscribe to the mailing list on proko.com

to get the latest and greatest tutorials.

See you next week.