teaching materials for persons
with visual impairment
Reading using the PC
- For persons with visual impairment (PWVI) using a PC, a software known as a "screen reader" is used. The output is in the form of synthesised speech and/or Braille through a refreshable Braille device. The most common screen reading software is "JAWS" which is available in many languages including English and Chinese.
- Essentially, JAWS will read anything on the screen that has a text base. It will not read images-based material, e.g. graphics and photos. File formats containing text components (hence readable by PWVI) include, MS Word (doc), simple text (txt), email (eml), Excel (xls), Power Point (ppt), webpages (htm/html) and text-based (called searchable) PDF (PDF). Of these, the most readable ones are the doc and txt, the doc being preferred for its ease of navigation with the cursor keys.
- If there is a choice, it is infinitely preferable to provide the doc format to students with visual impairment.
Figure caption (or ALT Tags)
- A brief text descriptive caption by an image or figure would be immensely helpful to readers with visual impairment. This would inform them of the existence of an unreadable image.
- Files in such formats as Microsoft Office, plain text and searchable PDF are readable by the Braille devices used by people with visual impairment. PDF files produced by most scanners are not readable by Braille scanners.
We can produce a searchable PDF file simply by clicking "save as" in Microsoft Office.
- Any PDF file containing a pure image has no text base and hence unreadable by PWVI. This is said to be unsearchable. A sighted person just looking at the screen cannot tell the difference as an unsearchable PDF image may appear to contain text although, in actual fact, the apparent text is part of an image. The screen reader JAWS would say "empty document” as it sees no embedded readable text base.
Documents from Scanning
- Most older scanners will scan a document and generate an image (unsearchable) PDF file. This is definitely useless to students with visual impairment. In fact, this is the major source of undesirable (unsearchable/unreadable) PDF files.
Searchable PDF from Scanning
- With newer models of scanners, the user has a choice of either an ordinary (unsearchable) or a good searchable output. The latter is normally obtained under the option called "scan document" rather than "scan picture". Basically the latter (searchable option) has built in an additional text-recognition procedure known as optical character recognition (OCR) which embeds the text base in the PDF file making the latter searchable for PWVI.
Converting from Bad to Good PDF
- For the technically minded, it is possible to convert an image (bad) PDF into searchable (good) PDF format using an OCR software. The software called Omnipage or Omnipage professional would perform this task. This procedure is only used as last resort (e.g. if the original doc file has been lost) as, apart from being time consuming, the accuracy of (OCR) is always limited.
Good Practice Re PDF
- To avoid the trouble mentioned in 6 and 9 above, it is infinitely preferable and more efficient to have a good PDF (searchable) file generated using the direct technique mentioned in 5. This would do away with the extra procedures of printing, scanning and OCR with an inferior output.
Online Electronic Materials
- Most online electronic materials, e.g. electronic journals, online newspapers and library resources are text-based, hence readable for PWVI.
Non ASCII (non-text) Characters
- In MS Word, apart from standard ASCII text characters, most of the symbols entered under the "insert/symbol" menu are readable with a special keystroke.
- It will be absolutely vital that e-mails and websites consistently implement and comply with accessibility requirements not least those for the visually impaired. This normally means screen reader readability (non-image) for all web elements (e.g. properly labelled links, graphical links and buttons) and also all downloadable documents (e.g. searchable/readable PDF files and doc/docx/txt/xls/xlsx text based files).