Update three-flashes-or-below-threshold.html #2127
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A first attempt at rewriting flashing assessment criteria
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while you're in that general area, might also be worth updating the links/resources that have relocated. change to and likewise change to I'd note that PEAT as a tool is also fairly useless nowadays in a world of responsive web design, as it effectively can only analyse content at a resolution of 1024x768 and does so by resizing your browser (where it can) to that size. might be worth noting somehow? |
provided changes to address patrick's comments.
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i've done a separate PR for updating the links (as mentioned in #2127 (comment)) #2132 (as that's a more straightforward change that is, likely, non-controversial) |
Your PR for that was merged in, so no need to replicate here. |
| evaluation. The 341 x 256 pixel block represents a 10 degree viewport at a typical | ||
| viewing distance. (The 10 degree field is taken from the original specifications and | ||
| represents the central vision portion of the eye, where people are most susceptible | ||
| to photo stimuli.) | ||
| </p> | ||
| <p>With the proliferation of devices of varying screen sizes (from small hand-helds to large living room displays), as well as the adoption of <a href="https://www.w3.org/TR/WCAG21/#dfn-css-pixels">CSS pixels</a> as a density-independent unit of measurement, the prior assessment criteria seem outdated. However, an image of a consistent size uses up relatively the same percentage of a user's visual field on any device. On a large screen, the image takes up less size, but the large screen takes up a larger part of the visual field. On a mobile screen, the image may take up most or all of the screen; however, the mobile screen itself takes up a smaller portion of the user's visual field. So the same dimension of the flashing content, represented in CSS pixels can still provide a consistent means of assessment. Substituting CSS pixels for the original pixel block means that the assessment becomes 341 x 256 CSS pixels, or a flashing area of 87,296 CSS pixels.</p> |
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the prior assessment criteria seem outdated reads a bit weird, especially since the next sentence clarifies why they're not. maybe the prior assessment criteria *may* seem outdated
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the assessment becomes 341 x 256 CSS pixels reads slightly off. maybe more accurately the threshold for the combined area of flashing becomes ...
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note that this still leaves questions open like #553 (comment) (about that relative luminance, and that however, i do think this closes #585 for me, so i'll add the github incantation to the top comment here |
| @@ -38,12 +38,15 @@ <h2>Intent of Three Flashes or Below Threshold</h2> | |||
| did not allow any flashing (even of a single pixel) within a broad frequency range | |||
| (3 to 50 Hz). This Success Criterion is based on existing specifications in use in | |||
| the UK and by others for television broadcast and has been adapted for computer display | |||
| viewing. The 1024 x 768 screen is used as the reference screen resolution for the | |||
| viewing. In WCAG 2.0, the 1024 x 768 screen was used as the reference screen resolution for the | |||
changes to accommodated feedback from Patrick and AWK
A first attempt at rewriting flashing assessment criteria
x-ref #1132
Closes #585