Thread Subject: 2.1.A - Contrast Ratio for Display

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From: Takemura, Michael (HP Accessibility)
Date: Thu, Oct 11 2007 6:10 PM

Rob...

The standard uses a method for contrast ratio measurement that is not
common in the industry. We use a direct measurement method such that CR
of 800:1 or 1000:1 is quite common. This proposed 508 standard uses a
calculation based on red, green and blue components in a ratio
determined by the sRGB set point. The max possible CR is 21:1.

We would need to conduct some lab experiments or calculations to see
what 5:1 looks like.

My interpretation of the rule is that the display must be at least 5:1.
Is that the way you read it, or does it need
to be exactly 5:1--that would be a problem.

Michael

Michael Takemura
HP, Director, Accessibility Program
www.hp.com/accessibility
281 518 0739

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