Extract 'ALT' Text from HTML into a Plain Text File and Insert it Back into HTML Again

(Version 1 & 3 respectively)

What Are They?

They are programs which extract 'ALT' text from an HTML document to a normal plain text file for easy editing and put it back into the HTML document again afterwards.

System Requirements

A Perl interpreter.

How to Use It

To Extract 'ALT' Text

Run 'HtmlImgAltTextExtract.pl'. It takes one parameter: the name (path with respect to current working directory) of the HTML file to extract from.

It will copy the 'ALT' text it finds in that file into a file with the same name as the HTML file but with 'AltText.txt' appended. It will not alter the original HTML file.

Text File Format

It is a very simple format. For each image the entry consists of:

The address of the image as written in the HTML. Followed by a line break.
The 'ALT' text. Followed by two line breaks.

To Insert 'ALT' Text

Run 'HtmlImgAltTextInsert.pl'. It takes two parameters: the names (paths with respect to current working directory) of the HTML file to insert into and the text file containing the 'ALT' texts to be inserted respectively.

Example Uses

As well as making editing the ALT text in an HTML document less cumbersome that editing the HTML source in a text editor or opening up a dialogue box for each image in a WYSIWYG HTML editor, it can be used for:

Copying 'ALT' text between HTML files: If they are in the same directory on the website (so paths to the images will be the same), simply extract the 'ALT' text from the one with it and insert it into the one without. (If two or more 2 sets of 'ALT' text from different pages need to be combined, simply concatenate the text files.)
Duplicating 'ALT' text for duplicated images: If your document has many repeated images such as a fancy bullet or a mathematical symbol done as an image then editing the 'ALT' text of each individually is very tedious and even a search & replace operation is a bit much. Instead simply write it for just one instance of the image, extract it to a text file and insert it back in. The inserter program will automatically apply it to all the identical images.
Checking for missing 'ALT' text: The extractor program clearly marks any images without 'ALT' text with the text "NO_ALT_TEXT" in the text file it produces.
Spellchecking: The extracted 'ALT' text can be put through a normal wordprocessor's spellchecker.

Known Deficiencies

The simple text file format cannot cope with double line breaks in ALT text because that is used as the record separator.
If the same image is accessed by two different paths (e.g. relative & absolute) then it will be counted as two separate images.
If the same image file is found with different ALT texts, only the last found text is used.
If the 'ALT' text contains double quotes then the inserter program simply converts them to single quotes to avoid conflict with the quotes surrounding surrounding the ALT text in the HTML instead of more intelligently escaping them.
It ignores commenting out of HTML sections so it may find spurious images. (I.e. it will put hidden image 'ALT' tags in the text file as well.)

Download

Download HtmlImgAltTextExtract.pl (3 Kb).
Download HtmlImgAltTextInsert.pl (5 Kb).

Other Perl Scripts, Disclaimers Etc.

See my computer programs index page for more simple useful computer programs.

Appendix: What is 'ALT' Text?

'ALT' text is the text alternative for an image in an HTML page.

It is written into the HTML <IMG> element, which specifies an image, by the value of its ALT (short for 'alternative') tag; hence its common name of 'ALT' text. For example <IMG SRC="Halibut1.jpg" ALT="An underwater photograph of a halibut swimming to the left."> would tell the web browser to display the JPEG image of the fish if it could display image or the text description of the fish if not.

Almost all images on web pages should have useful text alternatives because not all web browsers can usefully display images. For example, they might be running over very slow network links (e.g. mobile telephone modems), have small screens or the user might be blind (if you are making commercial web pages then you really need to take this into account as disabled accessibility is probably a legal requirement in addition to a way of increasing your customer base). Text alternatives also improve the chances of people finding your pages in the fist place because current web search engines are virtually all text based, not image based, even when they are being used to search for images.