Math & Images
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Requirements and suggested best practices for preparing images as part of NIMAS files have previously been established (NIMAS 1.1: the Technical Standard) and include guidelines pertaining to image size, format, resolution, etc. Math and Science content (i.e., works with equational and symbolic content) is often comprised of two types of images as well as text: 1. images that contain math content or information (such as graphs or illustrations), and 2. images of actual math (such as algorithms, symbols, etc.). Please note that the DAISY organization has approved MathML as an extension to the DAISY Z39.85-2005-2 standard and that the NIMAS will eventually implement MathML when appropriate tools and rendering software becomes available. Suggested recommendations and requirements for all NIMAS file set images include the following:
- Images that are part of a work must be included with that work (content must be complete and therefore must include that content's images)
- Images are to be provided in a folder as part of a NIMAS fileset, and placeholders within relevant XML document(s) are to indicate their location within the original work
- Images have preferred formats: SVG, PNG, or JPG format (in that order of preference)
- Images should be rendered in the same size/proportion as their (print) originals
- Images should be rendered in 300 dpi (dots per inch)
- Images should be named with relative path filenames in XML files (example: <img id="staricon4" src="./images/U10C02/staricon4.jpg" alt="star icon"/>)
- Images should be organized in folders with a hierarchical structure comparable to that of the original work (example: parent folder: images; child folder: U00, U01, U02; grandchild folder: U01C01, U01C02, U02C01, U02C02)—for more information about image organization in NIMAS filesets, see Creating NIMAS Files)
- Images should have file names relevant to their location within their original source, i.e., image names should be based on page number and position (example: p014-001.svg, EQp0213-004.jpg) and spaces should not be used in image file names
- Alt tag (alternative text) placeholders associated with images must be included in NIMAS XML source files; inclusion of alt tag text (i.e.; text equivalents of images) is strongly recommended
- Long description placeholders associated with images must be included if applicable (i.e., if warranted by the nature of the image); inclusion of long description text is recommended
Images and mark-up of math content differs somewhat from mark-up of other kinds of content and from treatment of other kinds of images. The following is taken from Creating NIMAS Files (CAST, Inc., 2006):
"Currently, a standard, problem-free way to treat mathematical content in terms of mark-up has not yet been developed. It has been proposed that, as an interim solution, math equations and other symbolic content be presented as images. When creating math content images, it is crucial to distinguish between content such as in-line equations, that are math content per se, and images, such as graphs, that just so happen to contain math content. The suggested best-practice for accomplishing this distinction is to code true math content with the notation EQ in image filenames to indicate that an image represents math content. Images such as charts and illustrations that contain or are about math should be coded as any other image would be. Examples are as follows:
- Filename of an image of an in-line equation: EQp212-004.jpg
- Filename of a pie chart: p010-002.jpg
- Filename of a symbol presented within text: EQp005-003.jpg
- Filename of an icon used throughout a math textbook: staricon.jpg
- Filename of an equation that recurs throughout a unit: EQdifferential2.jpg
A text description of EQ images must be provided for, either with alt tag placeholders or alt tag text and/or long description text. Coding in-line math content as images temporarily will make it accessible, because text descriptions will be recognized and read by text-to-speech software/readers."
Examples of NIMAS-conformant files with correct presentation of images within a NIMAS fileset can be found at the AIM web site Exemplars page.
Writing alt tag and long description text for Math images requires a careful approach. One important consideration is achieving consistency and extensibility: it is important to write description text that is consistent and it is important that this description text and the rationale behind it be comprehensible to the widest variety of users possible, both end-users of the text itself, such as students; and indirect users of the text, such as developers. A second and equally important consideration is to write description text that end-users will be able to understand and find useful; therefore it is important to consider the audience for the description text (for example, descriptions in a textbook used in grades 3–5 should be written with that grade range in mind).
Text descriptions of mathematical, i.e., equational, content should be written for the intended audience of that content and should be clear and easy to understand. When considering the writing of text descriptions, keep in mind the content audience’s age, capacity, and keep descriptions throughout a single work consistent in style and complexity. Users should be able to rely on the consistency of language used as an aid to access. For example, "one half" should not change to "one over two." Language used should match throughout a work. Works intended for a variety of audiences need careful consideration.
For blind and low-vision users, Mathspeak, created by A. Nemeth, is widely used and accepted because it is effective, easy to learn by both users and creators of descriptions, unambiguous, and comprehensive. It is recommended that Mathspeak be used to create text descriptions of mathematical content if the audience for the content to be described by Mathspeak warrants it—i.e., if end-users would be able to benefit from the use of Mathspeak. Even within the blind/low-vision population of users, for younger audiences and for audiences with little Math experience and knowledge, Mathspeak is not appropriate. In this case, adaptations should be made to Mathspeak or original, natural language descriptions should be written. Examples of text descriptions of Math images are shown below:
|Content||Audience 1: High School||Audience 2: Blind/Low Vision|
|alt tag||long description||alt tag||long description|
|sixty-four over one hundred1||none||B-frac six four over one zero zero E-frac||none|
|two over ninety-three||none||B-frac two over nine three E-frac||none|
|formula for velocity of a wavelength||v equals f multiplied by lambda or wavelength||v space equals space f lambda||none|
|Image of the process for converting units||This image shows the process for converting units in equation form. 150 g multiplied by 1 equals 150 kg multiplied by 1 kg over 1,000 g, equals 0.15 kg.||unit conversion equation||one five zero g dot one space equals space one five zero g dot B-frac one k g over one zero zero zero E-frac space equals space zero point one five k g|
1. Numerals are written out in this example to convey verbal format; "64" and the like can be used in XML documents because screen readers will voice "64" as "sixty-four."