This glossary is displayed as a reference for many of the terms used throughout the posts on this blog.
The definitions of these terms are based on my learning experiences, amongst other resources and may be edited as my understanding develops.
Form (noun)- A bulge, known as a convexity, or dent, known as a concavity, that can be seen on the surface of a three-dimensional structure. More formally known as a three-dimensional structure seen on the surface of an object.
The sphere shown above is a bulge(form) and there are many bulges(forms) on the hand cast.
Forms appear in a variety of sizes, the largest size being known as big forms, the middle size being known as sub-forms that sit on top of the big forms and the smallest size being known as microscopic micro-forms that sit on top of the sub-forms.
Transition (noun)- The path that connects two distinct convexities of form together.
A section of a transition in red.
Transitions are composed of 3 distinct points. The ending of the convexity from one form, the middle of the transition from one form into another and the beginning of the convexity into a new form.Plane (noun)- A flat surface of any size that faces the light in a specific direction.
A plane can be examined down to any size, even tiny microscopic micro-planes.
Block-in (noun)- A preliminary drawing that attempts to describe with line and sometimes value the shapes and structures that one sees on a subject.
Contour (noun)- The outline of the furthest edges of an object that one can see in their sight.
Although the egg continues to turn past the contour edge (outlined in white), the contour defines how much of the form one can see in their sight and thus creates an outline of an object.
Perspective (noun)- The view that one sees objects with from one's position, which causes objects to diminish as they recede from one's eyes.
All sides of the wall diminish in perspective.
Foreshortening (verb)- The diminishment in size of something as it recedes from one's eyes in perspective.
A barely foreshortened cube on the left, and a very foreshortened cube, viewed from above on the right.
Value (noun)- The degree of lightness or darkness of an area. Synonym- (Tone)
A representation of many values progressing from dark to light.
Gradation (noun)- The representation of form turning towards or away from a light source(s) by the use of value to show a progression of dark to light or vice versa depending on the situation.
A singular gradation is isolated on the right of the above image.
Optical (adj.)- Describing observations that are focused on how the values, shapes and gradations that one sees appear without consideration of the reasons for why what one sees appears the way it does.
Determining the specific value for each plane can be so difficult to determine by only evaluating and trying to retain an idea of each plane's orientation to a light source that it is useful to evaluate the lightness or darkness of a value for each plane.
Note, both optical and conceptual evaluations should describe the same aspects about a form, because we see shapes, values and gradations that are determined by the specific three-dimensional structure of a form and how it is oriented towards the light source.
By checking conceptual evaluations with optical evaluations there theoretically should be no difference in the shapes, values and gradations that are realized, just how they are realized.
Conceptual (adj.)- Describing observations that are focused on evaluating the reasons for why what one sees appears the way that is does.
There are many ways of analyzing visual appearances conceptually, including perspective, anatomy and examining a forms orientation to a light source(s).
The values one sees can seem so general and flat at first sight that it is useful to evaluate the position of each plane as it relates to the light source to gain understanding of the specific value that each plane should be represented by.
Note, both optical and conceptual evaluations should describe the same aspects about a form, because we see shapes, values and gradations that are determined by the specific three-dimensional structure of a form and how it is oriented towards the light source.
By checking conceptual evaluations with optical evaluations there theoretically should be no difference in the shapes, values and gradations that are realized, just how they are realized.
Modeling (verb)- The process of representing an illusion of form with value and or color on a two-dimensional surface. Also, the process of representing form with three-dimensional materials such as clay.
Marble (verb)- To evaluate the three-dimensional illusion on one's drawing by imagining rolling over the form(s) in one's drawing by hovering the point of one's pencil over a specific place on a form in one's drawing, looking to the same specific place on an actual form and running one's eye(that is on the actual form) in a single direction from that point at the same pace and direction that the pencil is moving on one's drawing across the same form(s), while one consistently shifts their gaze, while moving in this directional path, from the actual form to their drawing in order to make a tactile determination of whether some of the micro-planes in one's drawing need to turn more or less away from the light.
Picture Plane(noun)- An imaginary plane that can be thought of as located in between one's eye and the subject that one is viewing, on which the viewer sees an image of the subject through as if the picture plane is a thin piece of glass.
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| A person viewing a cube through the picture plane (K). From G.A Storey's, The Theory And Practice of Perspective (1910). |
The picture plane is always parallel to one's eyes and due to the roundness of the human eyeball, which allows one to look up, down and around, the picture plane can be thought of as being as curved as the shape of one's eyes.
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| Three sections of the rounded picture plane are required for the eye to look up and down to view the large blue pole. |
Light Source (noun)- The object that projects light onto its surroundings.
Photons are projected in every direction outwards from the light source.
Photon (noun)- A microscopic particle that describes the quantum of light energy. Photons are essentially microscopic pieces of light. Many photons are projected from light sources in the form of light rays.
A stream of photons projected in a laser beam in many light rays.
Light Ray (noun)- The directional path that photons of light, projected from a light source, travel in. Light rays generally travel in a singular direction from their source of a light source until they are interrupted by a substance of some solidity, which causes the light ray to reflect off of the surface in a new direction.
Microscopic photons travel in light rays.
Millions of light rays are projected from the light source in every direction, only a few light rays are shown in the diagram above.
Diffuse Reflection (noun)- Diffuse reflection occurs when light rays projected from a light source reflect at various angles from its meeting with the surface of form, in many cases due to irregularities in the microscopic surface of a form.
The example above show only a fraction of the portion of light rays emitted from a light source. In diffuse reflection, millions of light rays, composed of photons, are projected from the light source to meet the surface of a form and then reflect at various angles.
While the angles that the light rays from a light source are reflected at are various, the amount of light rays that reflect off of a given area of a form correlates to how much a form is facing towards or away from the light source.
The illustration above shows in a constricted sense, if only 7 light rays were projecting from the light source, more light rays would strike plane A than plane B, because plane A is more facing the angle of the light source. Since plane B is facing more away from the angle of the light source it receives less photons, and therefore less light, to reflect diffusely which causes plane B to appear darker in value.
The diffusely reflected light rays enter the eye at varying levels of brightness to create an image of a form under a light source(s).
Specular Reflection (noun)- Specular reflection is the mirror-like reflection of light on a smooth glossy surface where the angle of incoming light projected in a single direction from the light source, the angle of incidence, is reflected at the same angle into a viewer's eye, the angle of reflection. Therefore, the angle of incidence equals the angle of reflection. Specular reflection is only visible on a form at the halfway point between the angle of incidence and the angle of reflection into a viewer's eye.
A specular reflection shown above. Specular reflections are what make up highlights.
Highlight (noun)- The concentrated area of specular reflection on a form.
The highlight on the sphere is made up of many specular reflections. Since highlights are a mirror-like reflection of the light source, the highlight in the image above is less chromatic than the orange sphere.
Terminator (noun)- The boundary at which light rays from the primary light source can not reach on a form, which therefore defines the area of a form that is in shadow.
Form Shadow (noun)- The shadow area that is on an object which begins at the terminator.
Cast Shadow (noun)- The shadow that is created on a surface by an object that blocks the light from reaching the surface.
The cast shadow on the ground is created by the areas of the cube that block the light from reaching the ground.
Cast shadows adhere to the shape of the forms that they are cast on.
Form Light (noun)- The area of a form that is not in shadow.
High Form Light (noun)- The area on a form that is most facing the light source.
Reflected Light (noun)- Light that reflects within the shadow region of a form due to the orientation of forms facing the shadow region reflecting light into the shadow region on a form.
Synonym- Inter-Diffuse Reflection
On the left, an example of a light ray striking the white sphere and reflecting into the shadow of the black sphere, which consequently makes the areas of the shadow on the black sphere that receive reflected light brighter.
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