Principle One: Perceivable – Can the Reader Access the Content at All?

In my previous article, I mentioned that accessibility according to WCAG is based on four principles. Today, it's time to take a closer look at the first of them. This is absolutely fundamental, because if something isn't perceivable, it doesn't matter how technically or logically well-built it is.

Perceivable means that the user is able to perceive the content prepared by the publisher.

And it's not just about blind people.

This is extremely important, because if this condition is not met, the other principles have no chance of working.

What Does “Perceivable” Mean in Practice?

Content is perceivable when:

• it can be perceived through different senses or in different ways,

• it is not "trapped" in a single form of communication,

• does not require the user to have a specific way of seeing, hearing or perceiving colours.

For e-book publishers, this means one thing:

content cannot be solely visual.

The Most Common Problem? Content Hidden Within an Image

This is one of the most common errors in ebooks.

Examples:

• cover with the book title saved as an image, without text information about the title,

• an illustration containing an important quote, definition or command,

• a diagram, table or chart without any description.

For someone using a screen reader, such content simply doesn't exist. The reader only "sees" the image file. It doesn't know what's inside it.

From the publisher's point of view, this is often a surprise, because "everything is visible."

From the point of view of a blind reader, the book suddenly loses parts of its content, and in extreme cases, the entire text becomes meaningless.

 Alt Text – Small Item, Big Difference

Alt text is often treated as a technical chore. Instead, try looking at it differently: as an element of the book's narrative that allows for continuity of content regardless of how a user receives it.

It's not about describing every illustration as a "colourful picture” or a “pretty drawing."

It's about conveying its meaning.

Example:

• if an illustration has a decorative function, it is enough to indicate that it is decorative,

• if it shows a process, dependency, or data, the alt text should explain it.

alternative text is not a mere formality, but an element of the book's content.

Contrast and Readability – Not Only for Visually Impaired People

Perceivability also means:

• appropriate text-to-background contrast,

• not placing text in a photo,

• avoiding light grey text on a white background

• not confining information solely to colour.

A very common example:

“important fragments marked in red”.

If colour is the only medium for conveying information, some users simply won't perceive it. This includes people with colour vision impairments, those using high-contrast modes, those reading on e-readers with a limited colour palette, and those listening to ebooks, for whom content highlighted solely in colour is completely inaccessible. It's worth remembering that visually impaired readers use ebooks in a variety of conditions: on e-ink readers, in high-contrast modes, with enlarged text, and on small screens. An accessible ebook is one that doesn't fall apart when the user changes the viewing mode.

The good news is that improving contrast and readability boosts the comfort of reading for everyone, not just people with disabilities.

Perceivable Multimedia

If an ebook contains:

• audio recordings,

• videos,

• interactive elements,

then to make it perceivable you need to provide:

• video subtitles,

• transcriptions of recordings,

• descriptions of what is happening in the visual material.

This is not an addition "for some", but a way to maintain the full content.

Publishers often fear that this means enormous costs. In practice, a well-prepared text, which is already part of the publishing process, is often sufficient.

Why Is This Principle Crucial for Publishers?

“Perceivable” is a principle that quickly demonstrates that accessibility isn't an ideology or a perk. It's simply a condition for participating in reading culture, because perceivability is the moment when a reader either engages with content or is excluded from it from the outset.

If the content is not perceivable, the screen reader will not read it, so the user will not be able to use it, and in this case, even the best editing and proofreading will be irrelevant.

Accessibility doesn't start with the code - it starts with editorial decisions.

In the next article, we will look at the second accessibility principle – operable, i.e. whether the e-book can be used comfortably at all.

Bibliography:

 https://smartware.pl/zasady-dostepnosci-cyfrowej/

https://getknow.pl/kompletny-przewodnik-po-wytycznych-wcag-2-1-dla-dostepnosci-cyfrowej/

https://studioskladam.pl/kompendium-wcag-ebook/

https://www.krakweb.pl/struktura-i-zasady-wcag-kluczowe-filary-dostepnosci-cyfrowej

https://developer.mozilla.org/en-US/docs/Web/Accessibility/Guides/Understanding_WCAG/Perceivable

https://www.boia.org/blog/what-is-perceivability-in-web-accessibility-wcag-principles-explained

https://doc.bplogix.com/content/implementersreference/accessibility_principle_perceivable.html