Glossary

Alpha

Opacity

Alpha values are real numbers in the closed interval from 0 to 1, where 0 means full transparency, and 1 means full opacity.

Annotation Type

There are many annotation types defined in the PDF reference.

MuPDF supports the following types:

Text, FreeText, Square, Circle, Line, Polygon, PolyLine, Highlight, Underline, Squiggly, StrikeOut, Redact, Stamp, Caret, Ink, Popup, FileAttachment, Redaction

These types are not supported yet:

Sound, Movie, RichMedia, Widget, Screen, PrinterMark, TrapNet, Watermark, 3D, Projection

Associated File

TODO

Blend Mode

Blend modes define how a layer of graphics combines with a backdrop.

Below is an illustration of the visual effect for RGB colors for the blend modes defined for PDF.

For further details refer to the PDF specification’s section on blend modes.

Border Effect

Fancier borders can be drawn with a border effect:

None, Cloudy

Border Style

Annotations have have two border styles:

Solid, Dashed

More fancy borders are defined by the border effect.

CMYK JPEG

The situation with JPEG and CMYK colorspaces is complicated, and depends on many factors such as App markers, the ColorTransform PDF parameter, and whether a JPEG is intended as a standalone or embedded in PDF.

TODO: explain our behavior, and adobe’s behavior, and when impossible situations appear

File specification

In PDF a file specification names a file.

If a file specification only contains a file name or a path, then it represents an external file. Such a file is assumed to be found at the specified location in the file system.

A file specification may also embed the file contents as a stream inside the PDF. In this case the file specification represents an embedded file. For embedded files, further metadata may be stored (e.g. file size, creation and modification date).

For more details read the PDF specification’s section on file specifications.

Icon Name

Some annotations appear as an icon. The available icons differ per annotation type.

Text

Comment, Help, Insert, Key, NewParagraph, Note, Paragraph

FileAttachment

Graph, PaperClip, PushPin, Tag

Sound

Mic, Speaker

Stamp

Approved, AsIs, Confidential, Departmental, Draft, Experimental, Expired, Final, ForComment, ForPublicRelease, NotApproved, NotForPublicRelease, Sold, TopSecret

Knockout and Isolation

In a knockout transparency group each element overwrites the prior elements in the group instead of compositing with them.

In an isolated transparency group the group does not composite with the group’s backdrop, but rather a fully transparent backdrop.

For further details refer to the PDF specification’s sections on isolation and knockout.

Language code

Language codes consists of a primary code, followed zero or more by subcodes each preceded by a hyphen, e.g. “en”, “en-US”, “kr”, “zh-CN”, “zh-TW”.

For further details see the PDF specification’s section on Language Identifiers.

Line Cap Style

PDFs define three different shapes for the ends of unclosed subpaths: butt cap, round cap, and square cap. See below for the visual effect and refer to the PDF specifications section about Line Cap Styles for details.

Line Ending Style

Styles used to draw line endings for certain annotations. Below is an illustration with the name of each style. The example uses black line color, with both none and blue interior color.

Line Join Style

PDFs define three different shapes for the joining of two lines in a subpath: miter join, round join, and bevel join. See below for the visual effects and refer to the PDF specifications section about Line Join Styles for details.

MIME-type

A MIME-type is a string describing the type of data. PDF data has the MIME-type “application/pdf”, while unknown data has the MIME-type “application/octet-stream”. For further details see the specification that the PDF specification references: RFC 2048 - Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types.

Miter Limit

When mitered line joins are used, then lines joining at sharper and sharper angles will produce longer and longer miters. The miter may stick out longer than anticipated. Therefore PDF defines a miter limit value, at which a longer miter join will be changed to a bevel join. See below for the visual effects and refer to the PDF specifications section about Miter Limit for details.

Page Box

The PDF reference defines several boxes to determine different parts of a page. See the chapter on Page Boundaries for more details.

MediaBox

The MediaBox defines the size of the physical medium on which the page is to be printed. It includes items that will be physically trimmed from the final product like crop marks, registration marks, etc.

CropBox

The CropBox defines the visible region of the page to be displayed or printed. This has no real meaning, but is used to clip the page contents when rendering.

BleedBox

The BleedBox defines the region to which the page contents expect to be clipped. This includes any extra bleed area to account for imprecision in the printing process.

TrimBox

The TrimBox defines the intended dimensions of the finished page after trimming.

ArtBox

The ArtBox defines the area where it is considered safe to place graphical elements.

QuadPoint

A QuadPoint in PDF is a non-axis aligned quadrilateral, used to define areas on the page that typically cover text (which may be rotated, or skewed). It is given as an array of 8 numbers (four x, y pairs).

QuadPoints are used with Link and text markup annotations.

The order of the points is a matter of confusion, because the order used in the PDF reference doesn’t match the order that Adobe uses.

This is the order that is typically used:

[ ulx uly urx ury llx lly lrx lry ]

Standard Structure Type

The PDF specification defines how a PDF can specify a logical structure hierarchy of elements, similar to of HTML or XML. Each of the defined structure elements, e.g. Div, BlockQuote, P, H1-H6 etc., are associated with some visual content.

Widget Type

Widgets are a type of annotation. There are a few different subtypes:

Btn

Pushbutton, Check Boxes, Radio Buttons

Tx

Text Fields

Ch

Choice Fields (list box, combo box)

Sig

Signature Field

Winding

Non-zero Winding Number Rule

Even-Odd Rule

These rules in PDF defined what parts of a Path are inside and outside the curve respectively. This is used to determine what parts of a curve should be filled.

See the PDF specification sections on the Non-zero Winding Number Rule and Even-Odd Rule.