User:RexHandford/Sandbox

Shading is the process in which shadows and highlights are added, in reference to a light source to add the illusion of depth to a medium where such depth is not possible, such as on a 2D plane. Shading can be applied to nearly all variants of visual arts (when application is desirable) on both traditional and digital mediums. Adding shading to art will give an appearance of realism to the piece. Shading can be applied in a large variety of ways, ranging from cross hatching to smudging.

Application of Shading

In order for shading to exist in a piece, there must first exist at least one source of light in the picture. On traditional mediums, or digital ones that require full manual manipulation, the artist (change word?) is required to analyze how the light sources will affect the location of the shadows and highlights of the picture, and the darkness and lightness of those shadows and highlights.

Shading in portraiture, or other subjects which have complex surfaces will always require more effort than applying shading to a more standard object, such as a box or even a sphere. Shading involving subjects such as portraiture and figures might require at least some knowledge of anatomy in order to effectively understand where shading requires application, and the depth of that shading.

Shading on Traditional Mediums

Shading is a process used in drawing for depicting levels of darkness on paper by applying media more densely or with a darker shade for darker areas, and less densely or with a lighter shade for lighter areas. There are various techniques of shading including cross hatching where perpendicular lines of varying closeness are drawn in a grid pattern to shade an area. The closer the lines are together, the darker the area appears, but this effect is also dependent on the pressure being applied. Likewise, the farther apart the lines are, the lighter the area appears.

Smudging is another tactic that can be employed to shade a picture. This method involves adding lines of varying depths to a drawing (in accordance with the location of highlights and shadows) and then taking a material such as a tissue and rubbing the lines together, making the shading smooth. Smudging can be applied over the cross-hatch technique. The term has been recently generalized to mean that shaders are applied.

Light patterns, such as objects having light areas and shaded areas, help when creating the illusion of depth on paper and on computer screens.

Simple tutorials and lessons are available at numerous locations online to help learn the tips and tricks of shading to improve sketches. This is a Sample Tutorial^[1]

References

^ http://www.dueysdrawings.com/shading_tutorial.html

Shading on Digital Mediums

Application of depth with digital mediums can be done with methods very similar to those done on traditional mediums, such as paper. Many digital illustration programs, such as Adobe Photoshop and Corel Painter very closely mimic the properties of brushes and their behavior, and thus shading on a digital medium is comparable to shading traditionally. A graphics tablet is recommended for use with digital mediums, as most manufactures, such as Wacom manufacture pens that allow for pressure detection, so the heaviness and broadness of a stroke vary with the amount of pressure being applied downwards by the user. Such features further emulate a traditional drawing experience.

Most digital painting programs will offer controls over brushes such as Opacity and Flow. With these, the user can has a large amount of leverage over how the brush appears, and how shading is carried out with it.

Computer graphics

In computer graphics, Shading refers to the process of altering a color based on its angle to lights and its distance from lights to create a photorealistic effect. Shading is performed during the rendering process.

Angle to light source

Shading alters the colors of faces in a 3D model based on the angle of the surface to the sun or other light sources.

The very first image below has the faces of the box rendered, but all in the same color. Edge lines have been rendered here as well which makes the image easier to see.

The second image is the same model rendered without edge lines. It is difficult to tell where one face of the box ends and the next begins.

The third image has shading enabled, which makes the image more realistic and makes it easier to see which face is which.

Rendered image of a box. This image has no shading on its faces, but uses edge lines to separate the faces.

This is the same image with the edge lines removed.

Light sources

There are many types of lights:

Ambient Light - An ambient light lights all objects within a scene equally, brightening them without adding shading.
Directional Light - A directional light illuminates all objects equally from a given direction. It's like an area light of infinite size and infinite distance from the scene. There is shading, but cannot be any distance falloff.
Point Light - A point light originates from a single point, and spreads outward in all directions.
Spotlight - A spotlight originates from a single point, and spreads outward in a coned direction.
Area Light - An area light originates from a single plane and illuminates all objects in a given direction beginning from that plane.
Volume Light - A volume light is an enclosed space lighting objects within that space.

Shading is interpolated based on how the angle of these light sources reach the objects within a scene. Of course, these light sources can be and often are combined in a scene. The renderer then interpolates how these lights must be combined, and produces a 2d image to be displayed on the screen accordingly.

Distance falloff

Theoretically, two surfaces which are parallel, are illuminated the same amount from a distant light source, such as the sun. Even though one surface is further away, your eye sees more of it in the same space, so the illumination appears the same.

Notice in the first image that the color on the front faces of the two boxes is exactly the same. It appears that there is a slight difference where the two faces meet, but this is an optical illusion because of the vertical edge below where the two faces meet.

Notice in the second image that the surfaces on the boxes are bright on the front box and darker on the back box. Also the floor goes from light to dark as it gets farther away.

This distance falloff effect produces images which appear more realistic without having to add additional lights to achieve the same effect.

Two boxes rendered with an OpenGL renderer. Note that the colors of the two front faces are the same even though one box is further away.

The same model rendered using ARRIS CAD which implements "Distance Falloff" to make surfaces which are closer to the eye appear brighter.

Distance falloff can be calculated in a number of ways:

None
Linear - For every x units a given point is from the light source, the amount of light received is x units less bright.
Quadratic - This is approximately how light works in real life. A point that is twice as far from the light source as another will receive four times less light.
Factor of n - A point that is x units from a light source will receive 1/xⁿ as much light.
Any number of other mathematical functions may also be used.

Flat vs smooth shading

Flat shading is a lighting technique used in 3D computer graphics. It shades each polygon of an object based on the angle between the polygon's surface normal and the direction of the light source, their respective colors and the intensity of the light source. It was used for high speed rendering where more advanced shading techniques were too computationally expensive. But by the end of the 20th century affordable graphics cards were offering smooth shading that were also very fast, making flat shading for speed reasons unnecessary.

The disadvantage of flat shading is that it gives low-polygon models a faceted look. Sometimes this look can be advantageous though, such as in modeling boxy objects; flat shading is only inappropriate when the object must appear with smoother curves than actually modeled. Artists sometimes use flat shading to look at the polygons of a solid model they are creating. More advanced and realistic lighting and shading techniques include Gouraud shading and Phong shading.