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Computer Graphics
*****************
.. For writing style guide, see: :doc:`/about/contribute/style_guides/writing_guide`
If you add new entries, keep the alphabetical sorting!
.. glossary::
Baking
The process of computing and storing the result of a potentially time-consuming calculation
so as to avoid needing to calculate it again.
Bézier
A computer graphics technique for generating and representing curves.
BVH
Bounding Volume Hierarchy
A hierarchical structure of geometric objects.
See also `Bounding Volume Hierarchy <https://en.wikipedia.org/wiki/Bounding_volume_hierarchy>`__ on Wikipedia.
Double Buffer
Technique for drawing and displaying content on the screen.
Blender uses two buffers (images) to draw the interface in.
The content of one buffer is displayed while drawing occurs on the other buffer.
When drawing is complete, the buffers are switched.
Non-uniform Rational Basis Spline
NURBS
A computer graphics technique for generating and representing curves and surfaces.
OpenGL
The graphics system used by Blender (and many other graphics applications)
for drawing 3D graphics, often taking advantage of hardware acceleration.
See also `OpenGL <https://en.wikipedia.org/wiki/OpenGL>`__ on Wikipedia.
Pixel
The smallest unit of information in a 2D raster image,
representing a single color made up of red, green, and blue channels.
If the image has an :term:`alpha channel`, the pixel will contain a corresponding fourth channel.
Voxel
A cubicle 3D equivalent to the square 2D pixel.
The name is a combination of the terms "Volumetric" and ":term:`Pixel <pixel>`".
Used to store smoke and fire data from physics simulations.
Animation
=========
.. glossary::
Animation
Simulation of motion.
Bone
The building block of an :term:`Armature`. Made up of a :term:`Head`, :term:`Tail`
and :term:`Roll Angle` which define a set of local axes and a point of rotation at the :term:`Head`.
F-Curve
A curve that holds the animation values of a specific property.
Head
A subcomponent of a :term:`Bone`. The point of rotation for that :term:`Bone`.
Has X, Y and Z coordinates measured in the :term:`Local Space` of the :term:`Armature` :term:`Object`.
Used in conjunction with the :term:`Tail` to define the :term:`local <Local Space>` Y axis of the :term:`Bone`
in :term:`Pose Mode`. The larger of the two ends when drawn as an :term:`Octahedron`.
Inverse Kinematics
The process of determining the movement of interconnected segments of a body or model.
Using ordinary Kinematics on a hierarchically structured object you can, for example,
move the shoulder of a puppet. The upper and lower arm and hand will automatically follow that movement.
IK will allow you to move the hand and let the lower and upper arm go along with the movement.
Without IK the hand would come off the model and would move independently in space.
Keyframe
A frame in an animated sequence drawn or otherwise constructed directly by the user.
In classical animation, when all frames were drawn by animators,
the senior artist would draw these frames, leaving the "in between" frames to an apprentice.
Now, the animator creates only the first and last frames of a simple sequence (keyframes);
the computer fills in the gap.
Keyframing
Inserting :term:`Keyframes <Keyframe>` to build an animated sequence.
Non-linear Animation
Animation technique that allows the animator to edit motions as a whole,
not just the individual keys. Nonlinear animation allows you to combine,
mix, and blend different motions to create entirely new animations.
Posing
Moving, Rotating and Scaling the :term:`bones <Bone>` of an :term:`armature`
to achieve an aesthetically pleasing pose for a character.
Rig
A system of relationships that determine how something moves. The act of building of such a system.
Tail
A subcomponent of a :term:`Bone`. Has X, Y and Z coordinates measured in the :term:`Local Space`
of the Armature Object. Used in conjunction with the :term:`Head`
to define the :term:`local <Local Space>` Y axis of a :term:`Bone` in :term:`Pose Mode`.
The smaller of the two ends when drawn as an :term:`Octahedron`.
Walk Cycle
In animation, a walk cycle is a character that has just the walking function animated.
Later on in the animation process the character is placed in an environment
and the rest of the functions are animated.
Texturing
=========
.. glossary::
Bump Mapping
Technique for simulating slight variations in surface height using a grayscale "height-map" texture.
Environment Map
A method of calculating reflections.
It involves rendering images at strategic positions and applying them as textures to the mirror.
Now in most cases obsoleted by Raytracing, which though slower is easier to use and more accurate.
Glossy Map
See :term:`Roughness Map`.
Normal mapping
Is similar to :term:`Bump mapping`, but instead of the image being a grayscale heightmap,
the colors define in which direction the normal should be shifted,
the three color channels being mapped to the three directions X, Y and Z.
This allows more detail and control over the effect.
Procedural Texture
Computer generated (generic) textures. Procedural textures can be configured via parameters.
Roughness Map
A gray scale texture that defines how rough or smooth the surface of a material is.
This may also be known as a :term:`Glossy Map`.
Radiosity
A global lighting method.
that calculates patterns of light and shadow for rendering graphics images from three-dimensional models.
One of the many different tools which can simulate diffuse lighting in Blender.
See also
`Radiosity (computer graphics) <https://en.wikipedia.org/wiki/Radiosity_%28computer_graphics%29>`__
on Wikipedia.
Raytracing
Rendering technique that works by tracing the path taken by a ray of light through the scene,
and calculating reflection, refraction, or absorption of the ray whenever it intersects an object in the world.
More accurate than :term:`scanline`, but much slower.
Refraction
The change in direction of a wave due to a change in velocity.
It happens when waves travel from a medium with a given :term:`index of refraction` to a medium with another.
At the boundary between the media, the wave changes direction;
its wavelength increases or decreases but frequency remains constant.
Render
The process of computationally generating a 2D image from 3D geometry.
Texture
Specifies visual patterns on surfaces and simulates physical surface structure.
Texture Space
The bounding box to use when using *Generated* mapping to add a :term:`Texture` to an image.
UV Map
Defines a relation between the surface of a mesh and a 2D texture. In detail,
each face of the mesh is mapped to a corresponding face on the texture.
It is possible and often common practice to map several faces of the mesh to the same
or overlapping areas of the texture.
Rendering
=========
.. glossary::
Ambient Light
The light that comes from the surrounding environment as a whole.
Ambient Occlusion
A ratio of how much :term:`ambient light` a surface point would be likely to receive.
If a surface point is under a foot or table,
it will end up much darker than the top of someone's head or the tabletop.
Bounce
Refers to the reflection or transmission of a light ray upon interaction with a material.
See also :doc:`Light Paths </render/cycles/settings/light_paths>`.
Caustics
Bright concentrations of light focused by specularly reflecting or refracting objects.
Displacement Mapping
Method for distorting vertices based on an image or texture.
Similar to :term:`Bump Mapping`, but instead operates on the mesh's actual geometry.
This relies on the mesh having enough geometry to represent details in the image.
DOF
Depth Of Field
The distance in front of and behind the subject which appears to be in focus.
For any given lens setting, there is only one distance at which a subject is precisely in focus,
but focus falls off gradually on either side of that distance,
so there is a region in which the blurring is tolerable.
This region is greater behind the point of focus than it is in front,
as the angle of the light rays change more rapidly; they approach being parallel with increasing distance.
Diffuse Light
Even, directed light coming off a surface.
For most things, diffuse light is the main lighting we see.
Diffuse light comes from a specific direction or location and creates shading.
Surfaces facing towards the light source will be brighter,
while surfaces facing away from the light source will be darker.
Directional Light
The light that has a specific direction, but no location.
It seems to come from an infinitely far away source, like the sun.
Surfaces facing the light are illuminated more than surfaces facing away, but their location does not matter.
A Directional Light illuminates all objects in the scene, no matter where they are.
Field of View
The area in which objects are visible to the camera. Also see :term:`Focal Length <focal length>`
Focal Length
The distance required by a lens to focus collimated light.
Defines the magnification power of a lens. Also see :term:`Field of View <field of view>`.
Global Illumination
A superset of :term:`radiosity` and ray tracing.
The goal is to compute all possible light interactions in a given scene,
and thus, obtain a truly photo-realistic image.
All combinations of diffuse and specular reflections and transmissions must be accounted for.
Effects such as color bleeding and caustics must be included in a global illumination simulation.
Gouraud Shading
Used to achieve smooth lighting on low-polygon surfaces without the
heavy computational requirements of calculating lighting for each pixel.
The technique was first presented by Henri Gouraud in 1971.
IOR
Index Of Refraction
A property of transparent materials.
When a light ray travels through the same volume it follows a straight path.
However, if it passes from one transparent volume to another, it bends.
The angle by which the ray is bent can be determined by the IOR of the materials of both volumes.
Phong
Local illumination model that can produce a certain degree of realism in three-dimensional
objects by combining three elements: diffuse, specular and ambient for each considered point on a surface.
It has several assumptions -- all lights are points, only surface geometry is considered,
only local modeling of diffuse and specular, specular color is the same as light color,
ambient is a global constant.
Scanline
Rendering technique. Much faster than :term:`raytracing`,
but allows fewer effects, such as reflections, refractions, motion blur and focal blur.
Shading
Process of altering the color of an object/surface in the 3D scene,
based on its angle to lights and its distance from lights to create a photorealistic effect.
Specular light
A light which is reflected precisely, like a mirror.
Also used to refer to highlights on reflective objects.
Subsurface Scattering
Mechanism of light transport in which light penetrates the surface of a translucent object,
is scattered by interacting with the material, and exits the surface at a different point.
All non-metallic materials are translucent to some degree.
In particular, materials such as marble, skin,into account.
and milk are extremely difficult to simulate realistically without taking subsurface scattering
Film & Imagery
==============
.. glossary::
Action Safe
Area of the screen visible on most devices. Place content inside it to ensure it does not get cut off.
Aliasing
Rendering artifacts in the form of jagged lines.
Anti-aliasing
See :term:`oversampling`.
HDRI
High Dynamic Range Image
A set of techniques that allow a far greater dynamic range of exposures than normal digital imaging
techniques. The intention is to accurately represent the wide range of intensity levels found in real scenes,
ranging from direct sunlight to the deepest shadows.
See also `HDRI <https://en.wikipedia.org/wiki/HDRI>`__ on Wikipedia.
Matte
Mask
A grayscale image used to include or exclude parts of an image. A matte is
applied as an :term:`Alpha Channel`, or it is used as a mix factor when
applying :term:`Color Blend Modes`.
MIP
Mipmap
Mipmapping
'MIP' is an acronym of the Latin phrase 'multum in parvo', meaning 'much in little'.
Mipmaps are progressively lower resolution representations of an image,
generally reduced by half squared interpolations using antialiasing.
Mipmapping is the procces used to calculate lower resolutions of the
same image, reducing memory usage to help speed visualization, but increasing
memory usage for calculations and allocation. Mipmapping is also a procces
used to create small antialised samples of an image used for texturing.
The mipmapping calculations are made by CPUs, but modern graphic processors
can be selected for this task and are way faster.
See the Mipmap option present in the :doc:`System Preferences </preferences/system>`.
Motion Blur
The phenomenon that occurs when we perceive a rapidly moving object.
The object appears to be blurred because of our persistence of vision.
Simulating motion blur makes computer animation appear more realistic.
Multi-sampling
See :term:`FSAA`.
Oversampling
Is the technique of minimizing :term:`aliasing`
when representing a high-resolution signal at a lower resolution.
Also called Anti-Aliasing.
Overscan
The term used to describe the situation.
when not all of a televised image is present on a viewing screen.
See also `Overscan <https://en.wikipedia.org/wiki/Overscan>`__ on Wikipedia.
Premultiplied Alpha
See :term:`Alpha Channel`.
Projection
In computer graphics, there are two common camera projections used.
Perspective
A *perspective* view is geometrically constructed by taking a scene in 3D
and placing an observer at point *O*.
The 2D perspective scene is built by placing a plane (e.g. a sheet of paper)
where the 2D scene is to be drawn in front of point *O*,
perpendicular to the viewing direction.
For each point *P* in the 3D scene a *PO* line is drawn,
passing by *O* and *P*. The intersection point *S* between
this *PO* line and the plane is the perspective projection of that point.
By projecting all points *P* of the scene you get a perspective view.
Orthographic
In an *orthographic* projection,
you have a viewing direction but not a viewing point *O*. The line is then drawn
through point *P* so that it is parallel to the viewing direction. The intersection
*S* between the line and the plane is the orthographic projection of the point *P*.
By projecting all points *P* of the scene you get the orthographic view.
Straight Alpha
See :term:`Alpha Channel`.
Timecode
A coded signal on videotape or film giving information about the frame number, time of recording, or exposure.
Title Safe
Area of the screen visible on all devices.
Place text and graphics inside this area to make sure they do not get cut off.
Z-buffer
Raster-based storage of the distance measurement between the camera and the surface points.
Surface points which are in front of the camera have a positive Z value and
points behind have negative values. The Z-Depth map can be visualized as a grayscale image.
Objects
=======
.. glossary::
Child
An :term:`Object` that is affected by its :term:`Parent`.
Constraint
A way of controlling one :term:`object` with data from another.
Crease
Property of an :term:`edge`. Used to define the sharpness of edges in :term:`subdivision surface` meshes.
Curve
A type of object defined in terms of a line interpolated between Control Vertices.
Available types of curves include :term:`Bézier` and :term:`NURBS`.
Cyclic
Often referring to an object being circular. This term is often associated with :term:`Curve`.
Empty
An :term:`Object` without any :term:`Vertices`, :term:`Edges <Edge>` or :term:`Faces <Face>`.
Lattice
A type of object consisting of a non-renderable three-dimensional grid of vertices.
See also :doc:`Lattice Modifier </modeling/modifiers/deform/lattice>`.
Layer
A device for organizing objects. See also :doc:`Layers </editors/3dview/object/properties/relations/layers>`.
Object
Container for a type (Mesh, Curve, Surface, Metaball, Text, Armature,
Lattice, Empty, Camera, Lamp) and basic 3D transform data (:term:`Object Origin`).
Parent
An :term:`Object` that affects its :term:`Child` objects.
Parenting
Creating a :term:`Parent`-:term:`Child` relationship between two :term:`objects <Object>`.
Primitive
A basic object that can be used as a basis for modeling more complicated objects.
Vertex Group
Collection of :term:`vertices <vertex>`.
Vertex groups are useful for limiting operations to specific areas of a mesh.
Weight Painting
Assigning :term:`vertices` to :term:`Vertex Groups <Vertex Group>` with a weight of 0.0 - 1.0.