Page 78 - GIGW2

CH 06 Design

6.6.2 Size of image files should be minimised

The size of image files should be reduced as much as possible to minimise the
download time of web pages. A variety of techniques can improve the download
time of pages:

• Scaling of images should be avoided as they tend to distort when scaled.
Instead, a correct size should be prepared in image processing software.
• A thumbnail (a smaller version) for a large image and link to the full-size copy
should be provided where appropriate.

6.6.3 Images and other non text content MUST be made Accessible

• A meaningful explanatory text equivalent MUST be specified for images
and other non text content e.g. by using the ALT attribute. The ALT
text for an image is displayed before the image is fully downloaded. It
is the main source of image information for users of text-only browsers,
users of browsers with graphics turned off, and users who are sight
impaired. The description should summarise the content or purpose of the
image. For example, to use the description ‘Picture’ to explain a graphic
does not serve any purpose. The following situations are exceptions:

(i) If the non text content is a control or accepts input e.g. a submit button
then it must have a name describing the purpose of the control.

(ii) If the non text content is time based media (audio/video) then the
text equivalent provides a descriptive identification of the same.

(iii) If non-text content is a test or exercise that would be
invalid if presented in text, then text alternatives at least
provide descriptive identification of the non-text content.

(iv) If non-text content is primarily intended to create a
specific sensory experience, then text alternatives at least
provide descriptive identification of the non-text content.

(v) CAPTCHA: If the purpose of non-text content is to confirm that content
is being accessed by a person rather than a computer, then text alternatives
that identify and describe the purpose of the non-text content are provided,
and alternative forms of CAPTCHA using output modes for different types of
sensory perception are provided to accommodate different disabilities.

(vi) If non-text content is pure decoration, is used only for visual formatting,

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