Post on 02-Jan-2016
description
The Importance of Color Accessibility
Greg Kraus, North Carolina State University
Wayne Dick, California State University, Long Beach
Agenda
• Concepts• Visual Impairment Simulator• WCAG 2• Beyond WCAG 2• Contrast Testing Tools
Two questions we ask with color accessibility
1. Given moderate visual acuity loss, can a person read this content without the aid of assistive technologies?
2. If a person needs an assistive technology, does our content prevent them from modifying the content to meet their needs?
Planning for color and visual deficiencies
• There are a wide range of color deficiencies and visual impairments
• How do we plan for them all?
Visual Impairment Simulator
• NoCoffee• Chrome Extension
NoCoffee Interface
NoCoffee: Base Page
NoCoffee: Protanopia
NoCoffee: Light Blur
NoCoffee: Heavy Blur
NoCoffee: Macular Degeneration
Standards: Taking the guessing out of conformance
• WCAG 2– Color is not the sole means of conveying
information– Provide sufficient contrast based on the size of the
text and the conformance level desired
WCAG 2 (1.4.1): Use of Color
• Examples of violations– “Required fields are in red”– “Complete the blue section first”
WCAG 2 (1.4.3 and 1.4.6): Contrast
• Level AA and Level AAA Conformance• Ratios– 3:1 minimum acceptable contrast for standard text
and vision– 4.5:1 accounts for moderately low visual acuity (vision
loss equivalent to approximately 20/40)• typical visual acuity of people at roughly age 80
– 7:1 accounts for users who typically do not depend on assistive technologies for visual impairments (vision loss equivalent to approximately 20/80)
What Is Covered in WCAG Contrast Requirements?
• Text• Does NOT apply to– Logos– Inactive form elements– Purely decorative text– Incidental text in photos– Other UI elements
WCAG 2 Conformance Levels and Ratios
• Level AA– 18 pt. or 14 pt. bold 3:1– Smaller, 4.5:1
• Level AAA– 18 pt. or 14 pt. bold 4.5:1– Smaller, 7:1
• 18pt (1.5em, 150%)• 14pt (1.2em, 120%)
There is no average person with low vision
• 35+ critical structures in the human visual system• Multiple ways these structures can
break• Visual acuity, field loss and color
perception are the formal metrics of low vision, BUT• They neither detect nor predict the
impact of low vision on life.
Application to Contrast
• Contrast is about differences in brightness• If you want high contrast then the
text is bright and the background is dark or visa versa.• Bright light is painful to many
people with low vision
Application to Color
• Color Blindness– 3 types, accommodations conflict
• Retinitis Pigmentosa– Bright blue can cause damage
What to do: Create flexible content
• Use 3:1 and 4.5:1 contrast ratio as advised.• Drop the illumination on the screen and see
how dark you can get and keep text is readable.• Practice strict separation of presentation from
content• Anticipate users changing your color scheme.• Provide text enlargement with reflow to 300%.
What text resizing have to do with contrast?
• To accommodate a disability with no average person, you must be flexible.• A page that enlarge gracefully has a
high degree of flexibility.• The better you ensure flexibility the
better you enable individual needs for low vision: color, size, spacing, special formatting
Eyedropper Tools
• Colour Contrast Analyser• Desktop application for Windows and OS X• Strengths– Can choose any colors on the screen
• Weaknesses– Anti-aliasing of text– Text over a non-uniform background– Must manually check elements
Colour Contrast Analyser
Text Over Images
Anti-Aliased Text
Automated Tools
• WAVE• Web-based tool• Strengths– Automatically checks all color combinations– Can account for text size
• Weaknesses– Text over images– Text in images– Text over CSS3 gradients
WAVE11
22
33
44
55
Image Analysis
• Color Contrast Analyzer for Chrome• Chrome extension• Strengths– Checks the page as it is rendered
• Weaknesses– Cannot differentiate between text and other user
interface elements
Color Contrast Analyzer
Color Contrast Analyzer: Original Image
Color Contrast Analyzer: Mask
Color Contrast Analyzer: Text Over Images
Color Contrast Analyzer: Text in Images
Testing Color Palettes
• NC State Accessible Color Palette Evaluator• Web-based application• Build a color palette• Compare all of the color combinations to see
which have enough contrast
Sample Accessible Palette Evaluator
• Sample Accessible Palette Evaluator
Color Palette Tweaker
• Tanaguru• Web-based application• Pick two colors and adjust one of them to
make the contrast great enough to meet WCAG