RE: A color tutorial from Tom Jewett

> I think we are trying to help more than just colour blindness with our contrast algorithm.

Yes, absolutely!  I see that I did write “main purpose” below (and that was a mistake), but what I really meant to be emphasizing is the genesis of the formula came from addressing color blindness, where specific difficulties and remediation strategies were well understood.  Then it turns out that paying attention to luminosity contrast ratios helps will all kinds of low vision issues.  Certainly many people do not find the contrast sufficient as the ratio approaches 4.5:1.  But in terms of the algorithm allowing for false positives, and in the absence of clinical trials like the Lighthouse did back in the day, I still think it is useful reassurance to test the edge cases against other maths that we have (e.g, Protanopia, and Deuteranopia).


From: David MacDonald <david100@sympatico.ca>
Sent: Thursday, June 6, 2019 3:13 PM
To: Bruce Bailey <Bailey@Access-Board.gov>
Cc: w3c-waI-gl@w3. org <w3c-wai-gl@w3.org>
Subject: Re: A color tutorial from Tom Jewett

Hi Bruce

I think we are trying to help more than just colour blindness with our contrast algorithm.
https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html<https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.w3.org%2FTR%2FUNDERSTANDING-WCAG20%2Fvisual-audio-contrast-contrast.html&data=02%7C01%7CBailey%40access-board.gov%7C9569755b82db48bc4dce08d6eab300d5%7Cfc6093f5e55e4f93b2cf26d0822201c9%7C0%7C0%7C636954451873620349&sdata=MnAIddWiPmhER2nL7q6%2F8Y2mZhuMNDl8PeZIomPduJw%3D&reserved=0>

I think some people with low vision are disproportionately affected by perceived low contrast.

Having said that, I don't know what would need to be done to the algorithm to improve it, and without, as Gregg said, significant input by knowledgeable researchers, like Lighthouse did back in the day, who are sensitive to the great amount of research put into our current algorithm, with a proposal and a demonstration of the benefits of the improvements, I wouldn't revisit the algorithm.



Cheers,
David MacDonald