This exception is intended to separate pictures that have text in them from images of text that are done to replace text in order to get a particular look.
In this provision there is an exception that reads "that are part of a picture that contains significant other visual content,". Corporate visual guidelines beyond logo and logotype are not included in the exception. Stylized text, such as in corporate logos, should be treated in terms of its function on the page, which may or may not warrant including the content in the text alternative. Nor is text that for some reason is designed to be invisible to all viewers. Incidental text, such as in photographs that happen to include a street sign, are not included. This requirement applies to situations in which images of text were intended to be understood as text. The previously-mentioned contrast requirements for text also apply to images of text (text that has been rendered into pixels and then stored in an image format) as stated in Success Criterion 1.4.3. For example, for a 72 PPI image, an author would need to use approximately 19 pt and 24 pt font sizes in order to successfully present images of large-scale text to a user. When creating images of large-scale text, authors should ensure that the text in the resulting image is roughly equivalent to 1.2 and 1.5 em or to 120% or 150% of the default size for body text. 72 PPI or 96 PPI), specifying point sizes for fonts from within an image editing application can be unreliable when it comes to presenting text at a specific size. The ratio between sizes in points and CSS pixels is 1pt = 1.333px, therefore 14pt and 18pt are equivalent to approximately 18.5px and 24px.īecause different image editing applications default to different pixel densities ( e.g. Point sizes are based on the CSS pt size as defined in CSS3 Values. When evaluating this success criterion, the font size in points should be obtained from the user agent or calculated on font metrics in the way that user agents do. Since there are so many different fonts, the general measures are used and a note regarding fancy or thin fonts is included. "18 point" and "bold" can both have different meanings in different fonts but, except for very thin or unusual fonts, they should be sufficient. (See The American Printing House for the Blind Guidelines for Large Printing and The Library of Congress Guidelines for Large Print under Resources). 18 point text or 14 point bold text is judged to be large enough to require a lower contrast ratio. This allows authors to use a wider range of color choices for large text, which is helpful for design of pages, particularly titles. The contrast requirement for larger text is therefore lower. Text that is larger and has wider character strokes is easier to read at lower contrast. For example, if random words are used to create a background and the words could be rearranged or substituted without changing meaning, then it would be decorative and would not need to meet this criterion. Text that is decorative and conveys no information is excluded. Therefore, in the recommendation, the contrast is calculated in such a way that color is not a key factor so that people who have a color vision deficit will also have adequate contrast between the text and the background. Color deficiencies can affect luminance contrast somewhat. For people without color deficiencies, hue and saturation have minimal or no effect on legibility as assessed by reading performance (Knoblauch et al., 1991). The intent of this Success Criterion is to provide enough contrast between text and its background so that it can be read by people with moderately low vision (who do not use contrast-enhancing assistive technology).
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