シェーディング
シェーディング (British: shading) is technique to give a three-dimensional impression by contrast of the light and shade by three-dimensional computer graphics or illustration. I call it shading by the picture. It is different from 付影処理 (shadowing :shadowing) which adds a shadow to merely solid.
Table of contents
Picture
シェーディング (shading) is technique to describe by being darker on a gloomy part, and using art supplies on a bright part using art supplies lightly when I draw a picture on the newspaper. In シェーディング technique, there is the cross-hatching which describes a flight to commune with a right angle a lot while changing the space, and expresses a shadow. The part that the space of the line is small becomes the part which a shadow has dark. Similarly, the part that the space of the line is large becomes the bright part.
I can describe the picture which is felt as if there is depth in a newspaper by giving シェーディング in consideration of hit of the light to an object.
Computer graphics
With シェーディング in the computer graphics, I change a color in consideration of an angle of the light and the distance from a source of light and point to the processing to get the effect such as the photograph taken on a spot. シェーディング is a part of the rendering processing.
Simple example
シェーディング changes a surface color of the three-dimensional model based on the surface and the angle to cross of rays.
The lower left image is the thing which drew a cuboid, but describes all aspects in the same color. Because the contour of the aspect is created with a different color at the same time, it becomes easy to understand that it is a cuboid. The image of the middle draws the same model, and all aspects are the same expressions likewise. Because I do not create a contour, the border of the aspect is hard to be identified as an aspect, and there is not a three-dimensional impression at all. The right image gives シェーディング and it is more realistic and is easy to distinguish each aspect, too.
 The image of the box. I do not give シェーディング, but am identified as a solid in the abozzo of the aspect. |  It is a thing except the abozzo from the same image |  I made シェーディング on the same image. Because the angles with the source of light are different by an aspect, colors are different in each. |
Source of light
When I give シェーディング by three-dimensional computer graphics, I use following various sources of light.
- I light up all objects in the アンビエントライト (environmental light) - scene equally. Because the whole becomes the equal brightness without establishing the position of the source of light in particular, I do not put シェーディング.
- I guess uniform rays right with parallelism from the ディレクショナルライト (parallelism source of light) - direction that I set. I assumed the very far-off source of light such as the sunbeam, and シェーディング is performed, but the distance decrement to mention later is not generated.
- Light occurs from point light (point light source) - one point that there is, and rays open in all directions from there.
- Light occurs from spotlight - one point that there is, and rays spread into a cone that I set form.
- I set a certain area light (surface illuminant) - plane, and rays spread through the direction that I appointed from there.
- A source of light that only the range of the distance that I set in volume light - space touches.
シェーディング is interpolation based on these sources of light and surface angle of the object. Of course one scene can set plural sources of light and, actually, often produces it like that. The Ren dollar interpolates the composition of the rays from plural sources of light and produces a two-dimensional image according to it.
Distance decrement
When there were two parallel planes theoretically, the illumination of the light from the long-distance source of light such as the sunbeam is equal. The illumination is constant even if one mask is far all the time.
In the lower figure, I show シェーディング when I lighted up two cuboids with a different source of light. As for both cuboids, as for the aspect of the front, it is in the same color with the left image. Some front of the cuboid in front is more spirited with the right image. In addition, a floor becomes bright as a near part. As for the source of light of the right image, rays damp so that the distance from a source of light is far; is set. A more realistic image is provided without calling this "distance decrement" (distance falloff), and increasing sources of light.
 Two boxes which painted pictures in OpenGL Ren dollar. The distance from a viewpoint is different, but paints pictures with an identical color. |
There are several calculation methods of the distance decrement.
- When I assumed the distance with linear (the first) - source of light x, I reduce quantity of the light to arrive there in proportion to x.
- A property of the light in second - real world is near. When the distance from a source of light doubles, the quantity of the light to arrive becomes a quarter.
- When I assumed the distance with the n next - source of light x, I assume quantity of the light to arrive there 1/xn.
- I can use the function except these.
Flat shading and fluent シェーディング
The flat shading (flat shading) is a kind of the writing technique in the three-dimensional computer graphics. I give シェーディング based on the angle with the normal vector of the polygon to constitute an object and the direction of the source of light, and, as for the color, am decided according to strength of the light to light up the polygon (aspect). High-speed rendering is necessary and is used when higher シェーディング technique is not usable. However, シェーディング smooth very fast is possible and comes to rarely use the flat shading for a performance-like reason even if it is a common graphics card in the present days of the 21st century.
The fault of the flat shading is a point becoming visually where small planes form a line when I want to express a smooth curved surface. Such an appearance may be preferable if I want to draw a square-built object. Because a flat shading is easy to look at a shape during solid model production, it is used well. The realistic シェーディング technique that advanced more includes Gouraud shading and フォンシェーディング.
Allied item
This article is taken from the Japanese Wikipedia シェーディング
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