Glossary of Terms used in Digital Graphics

         



This glossary is a work in progress. New terms are added when a need for a definition is identified as part of the process of writing a new book.

The objective of this glossary is to provide definitions which are easily accessible and could be used by a student of computing or computer science.

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A   B   C   D   E   F   G   H   I   J   K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   Z   Go to bottom

A

There are no terms in this glossary beginning with the letter 'A'.

B

Bit map

This is a type of image composed of a grid of pixels. In the grid, each pixel represents a point of colour. The quality of the image is determined by the resolution; the number of pixels per unit of length and the colour depth; the range of colours that can be represented by each pixel. Bit maps are often used for images that need to show fine shading and subtle hues. A photograph is usually stored as a bit map. A bit map will have a relatively large size on disc in comparison with a vector graphic version of the same image. See also Vector Graphic.

BMP

This refers to a file extension for a bitmap image file. As indicated by the name a file in BMP format contains a bit map; a raster image. BMP files are not compressed.

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C

Cartesian co-ordinates

The use of a pair of numbers to represent the location of a point in a plane. These points are usually represented by the letters X and Y. A horizontal line of points crossing the origin is termed the X axis. A vertical line of points crossing the origin is termed the Y axis. The origin is the point where both X and Y values are zero (0:0). Cartesian co-ordinates are used to represent lines graphs. They are also used to indicate points in a vector graphic. They can also be used to relocate an image by processing and altering the co-ordinates using an algorithm giving the impression of movement; animation. A system of cartesian co-ordinates can also be referred to as a rectangular or orthogonal system. See also origin, X axis, Y axis and Z axis.

CMYK

This stands for Cyan, Magenta, Yellow and blacK. A method for combining colours typically used in hardcopy and traditional printing. A full range of colours can be created using different values for each of these basic components. See also RGB.

Colour depth

This is an indication of the range of colour that can be recorded for each pixel in an image. The colour depth is a factor of the number of bits available for each pixel. The higher the number of pixels per bit, the greater the range of colour variations that can be recorded. For example, 32 bit colour is capable of recording a wider range of colours than 8 bit colour systems.

Crop

To crop an image is to remove an outer section of that image. Cropping is usually done to focus on one area within an image by removing areas which are either unwanted or distracting. Crop tools are standard in most image editors. A crop is usually rectangular.

D

There are no terms in this glossary beginning with the letter 'D'.

E

There are no terms in this glossary beginning with the letter 'E'.

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F

File Extension

A classification for a file stored on a computer which indicates the way it has been stored; the file format. The file extension is indicated by a three or four-letter suffix after the file name. The file extension is used by the operating system to determine how the file should be opened and read, i.e., which application should be used to process the file. Typical file extensions in digital graphics include: jpeg, png, bmp and tiff.

Fill

The colour content of a vector graphic image. Fill colours are usually flat; the same tone across the image. If an image contains a gradient fill, it has probably been converted to a bit map.

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G

GIF

This stands for Graphics Interchange Format. This is a file format which incorporates lossless compression. A GIF is a very common file extension in digital graphics, but it is gradually being supplanted by the PNG file format.

H

There are no terms in this glossary beginning with the letter 'H'.

I

There are no terms in this glossary beginning with the letter 'I'.

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J

JPEG (JPG)

This stands for Joint Photographic Experts Group. A JPEG is a file format which compresses files using lossy methods. This file extension is typically used when storing photographs.

K

There are no terms in this glossary beginning with the letter 'K'.

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L

Layer

In digital images, layers are two-dimensional piece of imagery stacked so that they provide a complete image when viewed from the top of the stack. Layering is used to provide images which are visually richer; three dimensional or where the layers are semi-transparent with a greater range of colour tones than could be achieved using flat fill colours. In animation, moving layers independently can also be used to provide effects. Layers are stacked on the Z axis of an image.

Line

A two-dimensional mark joining two points.

Lossless compression

A method of compressing files in which the size of the files is reduced by replacing areas with the same value with a code. There are various algorithms for achieving this. The advantage of this method is that a reduction in footprint is less likely to result in a loss of data quality.

Lossy Compression

A method of compressing files in which the size of the files is reduced by removing sections of data. The disadvantage of this method is that the quality of the data after compression could be compromised.

M

There are no terms in this glossary beginning with the letter 'M'.

N

There are no terms in this glossary beginning with the letter 'N'.

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O

Origin

The origin is the point where both X and Y values in a cartesian system are zero (0:0). In simple terms, the point at which the X axis and the Y axis cross. The default position for the origin can vary from one editor to another. In spreadsheet graphs the origin is usually in the bottom left, in the Scratch editor it is in the dead centre of the screen. Browsers usually assume top right of a window as origin for the CSS box model. Knowing the location of the origin assumed by a specific piece of software can be important for ensuring that an image is being successfully manipulated by that software tool. See also Cartesian co-ordinates, X axis, Y axis and Z axis.

Orientation

This term refers to way an image is positioned. Orientation is usually either portrait; height greater than width, or landscape; width greater than height.

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P

Pixel

A single point of colour in a digital image. Pixel is often abbreviated as px.

Plane

A flat, two-dimensional surface. In mathematics, a plane is said to stretch to infinity. In digital editing environment, a plane usually stretches to the boundaries of the board or document being edited.

PNG

The file extension for Portable Network Graphics format images. This file format is becoming increasingly popular. PNG files are compressed using the lossless method.

Point

A single point of colour in a print image. Point is often abbreviated as Pt. or pt.

Q

There are no terms in this glossary beginning with the letter 'Q'.

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R

Raster

A raster image is one constructed in the form of a grid of pixels. It is roughly equivalent with a bit map.

RGB

This stands for Red, Green and Blue. A method for combining colours typically used in digital composition. A full range of colours can be created using different values for each of these basic components. See also CMYK.

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S

Sprite

A two-dimensional image used in animations. Sprites are usually vector graphics and resemble traditional cartoon images.

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T

Three dimensional (3d)

An image in three dimensions; height, width and depth. This is often achieved in digital graphics by constructing an image in layers.

TIFF

This stands for Tagged Image File Format. A tiff is an envelope format capable of containing both bit map and vector graphic elements. This is an uncompressed file format. As a consequence, tiff files can be relatively large in terms of the amount of space required to store them. Tiffs are often used as a storage method for images intended for high quality prints.

Two dimensional (2d)

An image with only two dimensions; height and width.

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U

Unit

Units of measurement in digital graphics are usually one of the following: pixel, point, inch, mm, cm.

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V

Vector graphic

A type of image composed of lines between points identified by XY co-ordinates and a fill. Vector graphics have the advantage of being scalable; the dimensions of the image can be changed without any resulting loss of quality. Diagrams, cartoons and logos are usually stored as vector graphics. A vector graphic will have a relatively small size on disc in comparison with a bit map version of the same image. As a consequence of their relatively small size and scalability, vector graphics are often the image type of choice for animations. See also Bit Map.

W

There are no terms in this glossary beginning with the letter 'W'.

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X

XY co-ordinates

See Cartesian co-ordinates.

X axis

A horizontal line of points crossing the origin in a two-dimensional plane is termed the X axis. The X axis is also known as the abscissa in mathematics.

Y

Y axis

A vertical line of points crossing the origin is termed the Y axis. The Y axis is also known as the ordinate in mathematics.

Z

Z axis

An axis which is at right angles to the plane of points described by a set of XY co-ordinates. While an XY system can be used to determine the location of a point in two dimensions a third co-ordinate (on the Z axis) is needed to identify the location of points in three dimensions. In practice, the Z axis often determines the sequence of layers in a still digital image. It also determines the sequence of layers in the CSS box model. (A definition for CSS can be found in the glossary of computing terms.)

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