Glossary

alpha

The transparency of an object (or pixel). If an object with a non-maximal value of Alpha is placed over another object, the second object will be visible under the first. In Inkscape, a value of Alpha of 255 means the object is completely opaque, while a value of 0 means it is fully transparent (not visible).

Animated Portable Network Graphic (APNG)

An open standard for animated bitmap graphics, the animated parallel of the PNG standard and an alternative to MNG. There is support for this format in Firefox 3 and Opera 9.5 but the PNG group has rejected this extension to the standard.

baseline

For text, the line on which most characters (i.e., x) rest. Some characters such as p extend significantly below the baseline. Other characters such as O usually extend a small amount below the baseline so that they optically appear to rest on the baseline. Inkscape can align text to a common baseline. Inkscape also uses the word to describe the point at which vertical text is aligned horizontally. The baseline is indicated by a small square when text is selected.

bitmap graphics

The description of a drawing using pixels (in contrast to vectors). Also refered to as raster graphics.

See Also vector graphics.

bounding box

The smallest rectangular box with sides parallel to the x and y axis that completely encloses an object. Note: In Inkscape, the bounding box is calculated assuming a round stroke Join and Cap style if the stroke is visible and the Visual bounding box option is selected in the Tools section of the Inkscape Preferences dialog. If the Geometric bounding box option is selected, only the nodes are considered in the calculating.

bump map

A bitmap graphics used to define the contour of a surface so that a lighting effect can be applied. The SVG specification uses the Alpha channel for this purpose in several of the Filter primitives. See: Wikipedia entry.

Cascading Style Sheets (CSS)

A way of controlling the layout and style of graphics objects (including text) through the use of external files. This allows the separation of content from presentation. It allows documents to be easily adapted for a variety of rendering methods such as printing and web display.

Computer-Aided Design (CAD)

Use of a computer for techinical design of objects. See: Wikipedia entry.

Cyan Magenta Yellow Key (Black) (CMYK)

A method for describing a color by the amount of cyan, magenta, and yellow needed to generate the color. This subtractive color model (where light is absorbed) is most often used in printing. As a good black is difficult to obtain using a mixture of these colors, a fourth ink, the Key or black, is also used. See: Wikipedia entry.

dots per inch (dpi)

The number of pixels per inch when printing or displaying a digitized image. Inkscape has a default resolution for exporting bitmaps of 90 dpi.

gamma

A correction factor to account for nonlinearity in a display device. More technically, the numerical value of the exponent of the power-law correction.

Gaussian distribution

Also called Normal distribution, a mathematical function that describes a distribution found often in statistics (e.g., the distribution of scores on a test). The relevance for Inkscape comes from the use of the distribution in the Gaussian Blur filter. The key point is that the color of a pixel is determined by the colors of nearby pixels in the source, weighting the nearest pixels more.

ghostscript

An open-source PostScript interpreter. See: Ghostscript Home Page.

Graphics Interchange Format (GIF)

A patented standard for compressing bitmap graphics supported by most web browsers. The open PNG standard is technically superior and should be the format of choice for lossless compressed bitmaps.

Graphics User Interface (GUI)

The interface a computer program presents to the user.

hexadecimal number

A way of representing a number using base 16 rather than the normal base 10. Very commonly used with computers. The base 10 numbers 0–9 are augmented by the letters a through f (which may or may not be capitalized) representing the numbers 10–15. For example, 31 in base 10 is written as 1F in hexadecimal (1 times 16 plus 15 is 31).

hue, saturation, value (HSL)

A method for describing a color using hue, saturation, and lightness. See: Wikipedia entry.

HyperText Markup Language (HTML)

See: Wikipedia entry. The original markup language for web pages. In the process of being superseded by XHTML.

Joint Photographic Experts Group (JPEG)

A standard for lossy compression of bitmap graphics supported by most web browsers. More suitable for photographs than line art.

kerning

The process of adjusting the space between letters in text to improve the appearance of the text. A classic example is that the A and v in Aviary should slightly overlap.

LaTeX

A system for producing high-quality documents commonly used in mathematics and physics documents. LaTeX is built on top of TeX. See: LaTeX home page.

Linear Red Green Blue Color Space (linearRGB)

A color space where the output intensity of a color is linearly proportional to the input value.

See Also Standard Red Green Blue Color Space.

Multipurpose Internet Mail Extensions (MIME)

An Internet standard originally developed for electronic mail that assigns to each type of document content a unique name so that clients (programs) can interpret the data correctly.

Multiple-Image Network Graphic (MNG)

An open standard for animated bitmap graphics, the animated parallel of the PNG standard. Unfortunately, there is little support for this format in web browsers.

name spaces

The use of tags to define a region in a file where certain definitions are applicable. For example, an XML file can contain both SVG and XHTML. Name spaces keep the two from conflicting with each other.

opacity

The property of an object that determines the visibility of an underlying object. Opposite of transparency.

See Also alpha, transparency.

PDF

Portable Document Format. A printing language created by Adobe that supersedes PostScript. See: Adobe PDF site.

pixel

Short for picture element. The smallest part of a digitized image that includes all the color information for a region. Computer screen resolutions are typically described as having some number of pixels per inch. The pixel (px) is the default user unit for SVG. Inkscape has a default resolution for exporting bitmaps of 90 pixels/inch (ppi). SVG viewers typically have a default resolution of either 72 or 90 ppi.

point

A unit derived from the days when printers used letters carved in metal blocks for printing. Various points have been defined. Inkscape uses the computer point, which is 1/72 of an inch or 0.35277 mm.

Portable Network Graphic (PNG)

An open standard for compressing bitmap graphics supported by most web browsers.

PostScript

A printing language created by Adobe. The language can be used to describe a document in a device-independent way. See: Adobe PostScript site.

px

See pixel.

red-green-blue (RGB)

A method for describing a color using the amount of each primary color present. See Wikipedia entry.

red-green-blue-alpha (RGBA)

The addition of Alpha (transparency) as a fourth component to a RGB specified color.

rubber band

The box drawn when click-dragging the mouse with the Select Tool or the Node Tool active. The objects or nodes within the box will be selected. The drag must begin over an area without an object or with the Shift key held down.

Scalable Vector Graphics (SVG)

An XML standard for describing a drawing using vector graphics. See: W3C SVG page.

Standard Red Green Blue Color Space (sRGB)

A very common standard created by HP and Microsoft for defining color use on monitors and printers. See Wikipedia entry. The basic property of this color space is that the output intensity for a color (e.g., red) is (roughly) exponentially dependent on the specified input value. All SVG colors are defined using this standard. In SVG, color interpolation is by default done in the sRGB space except for filters, which is by default done in the linearRGB color space.

See Also Linear Red Green Blue Color Space.

Tag Image File Format (TIFF)

A file format for storing high-quality images such as photographs or line drawings.

tool tip

A short dialog shown while the mouse cursor is above some part of window. A typical use is to describe the function of an icon.

transformation matrix

A 3 × 3 matrix that describes how an object is to be transformed. The upper-left 2 × 2 sub-matrix controls scaling, rotating, and skewing. While the upper-right 1 × 2 sub-matrix controls translations, the bottom row is not modifiable.

An advantage of using transformation matrices is that cumulative transformations can be described by simply multiplying the matrices that describe each individual transformation. Inkscape stores an object's transformation internally as a transformation matrix (which can be seen and modified with the XML Editor).

In non-matrix form, we have the transformation: x' = Ax + Cy + E and y' = Bx + Dy + F where (x', y') is the new coordinate of a point at (x, y).

With the above set of equations, it is easy to see that E is magnitude of a translation in the x direction and F is magnitude of a translation in the y direction. For scaling, A and D are the scale factors for the x and y directions, respectively. For a pure rotation, A = D = sin(theta) and B = −C = cos(theta) where theta is the angle of the desired rotation. For skewing, C and B control skewing parallel to the x and y axes respectively.

A transformation matrix is always defined with respect to some point. The internal representation is with respect to the internal coordinate system origin (upper-left corner of page).

transparency

The property of an object that determines the visibility of an underlying object.

See Also alpha, opacity.

Unicode

A standard for encoding characters for all the world's living languages as well as many historic ones. The character mapping for Unicode can be found at the Unicode organization's web pages.

Universal Resource Locator (URL)

The address of a web page, graphic, etc., on the WWW.

vector graphics

The description of a drawing using vectors (in contrast to bitmaps).

See Also bitmap graphics.

eXperimental Computing Facility (XCF)

The native format for Gimp. The acronym comes from the name of the student group at the University of California, Berkeley, that gave birth to Gimp.

eXtensible HyperText Markup Language (XHTML)

An XML markup language for web pages. See: Wikipedia entry.

XLink

XML Linking Language. A language for creating sophisticated links between documents. Similar to the simpler URL. The SVG specification uses simple Xlinks.

eXtensible Markup Language (XML)

The underlying format for SVG files. See: Wikipedia entry.

z-order

The order in which objects are drawn when they overlap each other. Objects drawn on top are higher up in z-order. Unless explicitly changed, the most recent object created is on top.