Pdf To Epub On Mac
Sofie Kovalcheck
EPUB is an e-book file format that uses the ".epub" file extension. The term is short for electronic publication and is sometimes stylized as ePub. EPUB is supported by many e-readers, and compatible software is available for most smartphones, tablets, and computers. EPUB is a technical standard published by the International Digital Publishing Forum (IDPF). It became an official standard of the IDPF in September 2007, superseding the older Open eBook (OEB) standard.[2]
The Book Industry Study Group endorses EPUB 3 as the format of choice for packaging content and has stated that the global book publishing industry should rally around a single standard.[3] The EPUB format is implemented as an archive file consisting of XHTML files carrying the content, along with images and other supporting files. EPUB is the most widely supported vendor-independent XML-based e-book format; that is, it is supported by almost all hardware readers.[4]
The EPUB 3.0 specification became effective in October 2011, superseded by a minor maintenance update (3.0.1) in June 2014.[7] New major features include support for precise layout or specialized formatting (Fixed Layout Documents), such as for comic books,[8] and MathML support. The current version of EPUB is 3.2, effective May 8, 2019.[9] The (text of) format specification underwent reorganization[10] and clean-up; format supports remotely hosted resources and new font formats (WOFF 2.0 and SFNT)[11] and uses more pure HTML and CSS.[12]
EPUB 2.0 was approved in October 2007, with a maintenance update (2.0.1) intended to clarify and correct errata in the specifications being approved in September 2010.[6] EPUB version 2.0.1 consists of three specifications:
EPUB internally uses XHTML or DTBook (an XML standard provided by the DAISY Consortium) to represent the text and structure of the content document, and a subset of CSS to provide layout and formatting. XML is used to create the document manifest, table of contents, and EPUB metadata. Finally, the files are bundled in a zip file as a packaging format.
An EPUB file uses XHTML 1.1 (or DTBook) to construct the content of a book as of version 2.0.1. This is different from previous versions (OEBPS 1.2 and earlier), which used a subset of XHTML. There are, however, a few restrictions on certain elements. The mimetype for XHTML documents in EPUB is application/xhtml+xml.[15][a]
Styling and layout are performed using a subset of CSS 2.0, referred to as OPS Style Sheets. This specialized syntax requires that reading systems support only a portion of CSS properties and adds a few custom properties. Custom properties include oeb-page-head, oeb-page-foot, and oeb-column-number. Font-embedding can be accomplished using the @font-face property, as well as including the font file in the OPF's manifest (see below). The mimetype for CSS documents in EPUB is text/css.[15][b]
EPUB also requires that PNG, JPEG, GIF, and SVG images be supported using the mimetypes image/png, image/jpeg, image/gif, image/svg+xml. Other media types are allowed, but creators must include alternative renditions using supported types.[15] For a table of all required mimetypes, see Section 1.3.7 of the specification.
Unicode is required, and content producers must use either UTF-8 or UTF-16 encoding.[15] This is to support international and multilingual books. However, reading systems are not required to provide the fonts necessary to display every Unicode character, though they are required to display at least a placeholder for characters that cannot be displayed fully.[15]
The OPF specification's purpose is to "[define] the mechanism by which the various components of an OPS publication are tied together and provides additional structure and semantics to the electronic publication".[16] This is accomplished by two XML files with the extensions .opf and .ncx.
The OPF file, traditionally named content.opf, houses the EPUB book's metadata, file manifest, and linear reading order. This file has a root element package and four child elements: metadata, manifest, spine, and guide. Furthermore, the package node must have the unique-identifier attribute. The .opf file's mimetype is application/oebps-package+xml.[16]
The metadata element contains all the metadata information for a particular EPUB file. Three metadata tags are required (though many more are available): title, language, and identifier. title contains the title of the book, language contains the language of the book's contents in RFC 3066 format or its successors, such as the newer RFC 4646 and identifier contains a unique identifier for the book, such as its ISBN or a URL. The identifier's id attribute should equal the unique-identifier attribute from the package element.[16][c]
The manifest element lists all the files contained in the package. Each file is represented by an item element, and has the attributes id, href, media-type. All XHTML (content documents), stylesheets, images or other media, embedded fonts, and the NCX file should be listed here. Only the .opf file itself, the container.xml, and the mimetype files should not be included.[16]
The spine element lists all the XHTML content documents in their linear reading order. Also, any content document that can be reached through linking or the table of contents must be listed as well. The toc attribute of spine must contain the id of the NCX file listed in the manifest. Each itemref element's idref is set to the id of its respective content document.[16]
The guide element is an optional element for the purpose of identifying fundamental structural components of the book. Each reference element has the attributes type, title, href. Files referenced in href must be listed in the manifest, and are allowed to have an element identifier (e.g. #figures in the example).[16][d]
Of note here is that the values for the docTitle, docAuthor, and meta name="dtb:uid" elements should match their analogs in the OPF file. Also, the meta name="dtb:depth" element is set equal to the depth of the navMap element. navPoint elements can be nested to create a hierarchical table of contents. navLabel's content is the text that appears in the table of contents generated by reading systems that use the .ncx. navPoint's content element points to a content document listed in the manifest and can also include an element identifier (e.g. #section1).[16][18]
A description of certain exceptions to the NCX specification as used in EPUB is in Section 2.4.1 of the specification. The complete specification for NCX can be found in Section 8 of the Specifications for the Digital Talking Book.[18]
An EPUB file is a group of files that conform to the OPS/OPF standards and are wrapped in a ZIP file.[19] The OCF specifies how to organize these files in the ZIP, and defines two additional files that must be included.
The mimetype file must be a text document in ASCII that contains the string application/epub+zip. It must also be uncompressed, unencrypted, and the first file in the ZIP archive. This file provides a more reliable way for applications to identify the mimetype of the file than just the .epub extension.[17]
Also, there must be a folder named META-INF, which contains the required file container.xml. This XML file points to the file defining the contents of the book. This is the OPF file, though additional alternative rootfile elements are allowed.[17]
The EPUB 3.0 Recommended Specification was approved on 11 October 2011. On June 26, 2014, EPUB 3.0.1 was approved as a minor maintenance update to EPUB 3.0. EPUB 3.0 supersedes the previous release 2.0.1.[e]
EPUB 3.2 was announced in 2018,[26] and the final specification was released in 2019.[27] A notable change is the removal of a specialized subset of CSS, enabling the use of non-epub-prefixed properties. The references to HTML and SVG standards are also updated to "newest version available", as opposed to a fixed version in time.[28]
An EPUB file can optionally contain DRM as an additional layer, but it is not required by the specifications.[35] In addition, the specification does not name any particular DRM system to use, so publishers can choose a DRM scheme to their liking. However, future versions of EPUB (specifically OCF) may specify a format for DRM.[17]
The EPUB specification does not enforce or suggest a particular DRM scheme. This could affect the level of support for various DRM systems on devices and the portability of purchased e-books. Consequently, such DRM incompatibility may segment the EPUB format along the lines of DRM systems, undermining the advantages of a single standard format and confusing the consumer.[36][37][38][39][40][41]
EPUB is widely used on software readers such as Google Play Books on Android and Apple Books on iOS and macOS and Amazon Kindle's e-readers, but not by associated apps for other platforms. iBooks also supports the proprietary iBook format, which is based on the EPUB format but depends upon code from the iBooks app to function.[42]
EPUB is a popular format for electronic data interchange because it can be an open format and is based on HTML, as opposed to Amazon's proprietary format for Kindle readers. Popular EPUB producers of public domain and open licensed content include Project Gutenberg, Standard Ebooks, PubMed Central, SciELO and others.
Authors need to be aware that scripting in an EPUB Publication can create security considerations that are different from scripting within a Web browser. For example, typical same-origin policies are not applicable to content that has been downloaded to a user's local system. Therefore, it is strongly encouraged that scripting be limited to container constrained contexts.
An EPUB file is an archive that contains, in effect, a website. It includes HTML files, images, CSS style sheets, and other assets. It also contains metadata. EPUB 3.3 is the latest version. By using HTML5, publications can contain video, audio, and interactivity, just like websites in web browsers.[32]
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