apca-introduction

commit

13c1be744cbdd4f9079afaa2a2911a477460b63d

parent

6afe5c2670ea4113cc1622828910d5ae5b675fcb

Author

Tobias Bengfort <tobias.bengfort@posteo.de>

Date

2023-09-14 14:32

analysis: better explain impact of exponents

Diffstat

1 files changed, 7 insertions, 7 deletions

diff --git a/analysis.md b/analysis.md

@@ -333,14 +333,14 @@ value in WCAG 2.x to 0.4 we would get results much closer to APCA. And if we
  333   333 were to change the exponents in APCA to 1/3 we would get results much closer to
  334   334 WCAG 2.x.
  335   335 
   -1   336 Our vision adapts to the lighting conditions. In the dark, we are much better
   -1   337 at discerning dark colors. A lower exponent models these darker conditions.
  336   338 The most complete (but also most complex) color appearance model currently
  337    -1 available is [CIECAM02](https://en.wikipedia.org/wiki/CIECAM02). Its definition
  338    -1 of lightness can be approximated as `100 * pow(Y, 0.42 * c * z)`, where `c` and
  339    -1 `z` are parameters that depend on the lighting conditions.  The total exponent
  340    -1 can have values between 0.31 and 0.72.
  341    -1 
  342    -1 Given that model, WCAG 2.x is on the lower (darker) end of possible exponents,
  343    -1 while APCA goes to the other (lighter) extreme.
   -1   339 available is [CIECAM02](https://en.wikipedia.org/wiki/CIECAM02). It uses
   -1   340 exponents between 0.31 and 0.72. Given that model, WCAG 2.x is on the lower
   -1   341 (darker) end of possible exponents, while APCA goes to the other (lighter)
   -1   342 extreme. Choosing the right parameters depends on which lighting conditions we
   -1   343 want to model, and that is ultimately a policy decision.
  344   344 
  345   345 It seems reasonable to use a lower exponent for light-on-dark color pairs.
  346   346 First, because the background color itself is often a significant part of the