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Tools - Luminosity Contrast Ratio Analyser 1.1

This software has been superceded

A new Contrast Analyser is now available

Italian version: Versione italiana: Contrast Analyser - Versione 2.0

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What is the Luminosity Contrast Ratio Analyser?

It is primarily a tool for checking foreground & background colour combinations to determine if they provide good colour visibility. It also contains functionality to create simulations of certain visual conditions such as colour blindness.

Determining "colour visibility" is based on the Luminosity Contrast Ratio algorithm, suggested by the World Wide Web Consortium (W3C):

Note: It's important to remember that the luminosity contrast ratio is not yet a W3C recommendation; it is suggestion by the WAI WCAG 2.0 working group to help determine whether or not the contrast between two colours can be read by people with colour blindness or other visual impairments.

Luminosity Contrast Ratio

(L1+.05) / (L2+.05) where L is luminosity and is defined as .2126*R + .7152*G + .0722B using linearised R, G, and B values. Linearised R (for example) = (R/FS)^2.2 where FS is full scale value (255 for 8 bit color channels). L1 is the higher value (of text or background) and L2 is the lower value.

The Gamma correction and RGB constants are derived from the Standard Default Color Space for the Internet (sRGB) , and the 0.05 offset is included to compensate for contrast ratios that occur when a value is at or near zero, and for ambient light effects.

The Gamma correction and RGB constants are derived from the Standard Default Color Space for the Internet (sRGB) , and the 0.05 offset is included to compensate for contrast ratios that occur when a value is at or near zero, and for ambient light effects.

Text or diagrams and their background must have a luminosity contrast ratio of at least 5:1 for level 2 conformance to guideline 1.4, and text or diagrams and their background must have a luminosity contrast ratio of at least 10:1 for level 3 conformance to guideline 1.4.

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Uses

The Luminosity Contrast Ratio Analyser (LCRA) is useful to help determine, in particular, the legibility of text on a web page and the legibility of image based representations of text.

Assessing conformance with Checkpoint 2.2 of the Web Content Accessibility Guidelines 1.0

Checkpoint 2.2 of the WCAG 1.0 requires that

"foreground and background colour combinations provide sufficient contrast when viewed by someone having colour deficits, or when viewed on a black and white screen."

Assessing conformance with Guideline 1.4 of WCAG 2 (draft)

Guideline 1.4 of WCAG 2 (draft) states, make it easy to distinguish foreground information from background images or sounds.

The luminosity contrast ratio algorithm will become a recommendation when WCAG 2 becomes a recommendation if it is still listed in the guidelines. The algorithm was developed by Gregg Vanderheiden, Dave Kelso, and Aries Arditi at the Trace R&D Center.

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Using the LCRA

The user interface consists of 5 sections
  1. Colour Choice
  2. Results
  3. Colour Blindness Results
  4. Simulations
    • Select Window (list)
    • Select Image File
    • Simulation Viewer
  5. Options & Help Menus

1. Colour Choice

The Colour Choice controls are divided into 2 sections (foreground & background) each has 4 ways to choose a colour to test.

Interface para escolha da cor

  1. Colour pallet(s) accessed via a select box. Use this to help you test and choose suitable colour combinations.

    Paleta de cores

    The bottom (smaller) colour pallet consists of 10 shades of the currently selected base colour, located top-left, at varying degrees of opacity. The top row emulates opacity over a white background, the bottom over black . The opacity values are 100% opaque, 75%, 50%, 25% and 10% on the top row. The bottom row begins at 85% rather than 100% and continues on as the first.

    This pallet is useful for testing lighter and darker shades of the base colour, which may improve the visibility of the colour combination being tested.

    Note: This feature was inspired by the Color Palette Creator.

  2. Input of a colour value (in Hexadecimal or RGB format) into a text box. Useful if you have access to the Hex or RGB values of colours you want to check.

    Note: The colour value format can be changed via the "options > displayed colour value" menu

    hex value input box RGB input boxes

  3. Sampling of a colour from a web page (or anywhere else on the screen) using a magnifying colour sampler. colour sampler button

    Useful for quickly sampling, checking and obtaining the hex values of colours. Once the colour sampler button is selected a magnified area will appear around the cursor. The colour of the content under the tip of the cursor will appear in the colour pallet select box

    Once a colour is chosen with the colour sampler (left mouse click or 'enter' key) its hex value will appear in the 'hex value' text box and the results section will be updated to reflect the brightness and colour differences for the currently selected colour combination.

    Note: For fine control of the cursor use the arrow keys.

    Example of the magnified area around the cursor that occurs when the colour sampler is activated. The colour under the cursor tip appears in the colour pallet select box

  4. Red/Green/Blue slider controls

    red green and blue colour slider controls

    The slider controls were inspired by the colour contrast check at snook.ca. Thanks to pixeldiva for suggesting their inclusion

2. Results

The results section is divided into pass/fail icon & sample text results and full results: A pass is indicated by a Tick. A fail is indicated by a cross. A text box containing text in the foreground colour tested and a background using the background colour tested

pass/fail icon and sample text

The 'Full Results' displays the the colour values tested, result values for the test and what the pass/fail criteria are and indicates whether the contrast was found to be sufficient/insufficient.

Note: The results can be copied to the clipboard by activating the "copy results" button copy results button

results of the contrast check

3. Colour Blindness Results

Selecting the 'also show contrast results for colour blindness' check box will display summary results for 'normal vision' and 3 types of colour blindness (Protanopia, Deuteranopia, Tritanopia).

example colour blindness results

Note: The method of determining the colour value transformations for the 3 types of colour deficiency is from an algorithm described by Hans Brettel , Francoise Vienot and John Mollon in a paper which appeared in the Journal of the Optical Society of America V14, #10 pp2647.

Acknowledgements to the kind people at Vischeck who allowed us access to the source code of their implementation of the Brettel algorithm.

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4. Options, Simulations & Help Menus

Options

Selecting the 'always on top' menu item will keep the LCRA window on top of all other windows that are open. Selecting 'font' menu item opens a dialog box that allows you to modify the font used for the text labels and content of the LCRA. selecting the 'displayed colour values' allows a choice between Hex and RGB.

Note: selecting some font types or sizes can result in clipping of text content.

Options menu

Simulations

Documentation yet to be written....

Help

Selecting the "help" Menu item Help menu will open the LCRA documentation web page in a browser window.

Note: you will need to be connected to the internet to access the documentation.

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Use via Keyboard

Luminosity Contrast Ratio Analyser Access keys
FunctionKey(s)
move through all controlstab key
open foreground colour pallet(s)F9
open background colour pallets(s)F10
move through colour palletsarrow keys or the tab key
activate foreground colour samplerF11
activate background colour samplerF12
move colour samplerarrow keys
choose colour in sampler or palletEnter
move red, green, blue slider controlsarrow keys
always on topctrl+S
displayed colour value - hexctrl+E
displayed colour value - RGBctrl+R
simulations - select window listctrl+I
helpctrl+H

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Terms of Use Notice:

The Luminosity Contrast Ratio Analyser is Freeware.

By accessing or using the Luminosity Contrast Ratio Analyser, you acknowledge that you have read, understood and agree to be bound by the Luminosity Contrast Ratio Analyser Terms of Use.

THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED WARRANTY. IN PARTICULAR, VISION AUSTRALIA DOES NOT MAKE ANY REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE RELIABILITY, QUALITY, OR MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE. ADDITIONALLY, WAT-C DOES NOT GUARANTEE THAT USE OF THIS SOFTWARE WILL ENSURE THE ACCESSIBILITY OF YOUR WEB CONTENT OR THAT YOUR WEB CONTENT WILL COMPLY WITH ANY SPECIFIC WEB ACCESSIBILITY STANDARD.

This work is licensed under a Creative Commons License Creative Commons Licence.

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Download and Installation Instructions

Please Note: The Luminosity Contrast Ratio Analyser does not contain any adware or spyware.

System Requirements

  • Microsoft Windows - Tested on Windows 2000 & XP

This software has been superceded

A new Contrast Analyser is now available

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