apca-introduction

commit

3abe9e6cef2e0f75cfe36dff19fb0184a244cd13

parent

7d4009352edc1ce52bbb93eabb2403cc7f3f4522

Author

Tobias Bengfort <tobias.bengfort@posteo.de>

Date

2022-08-19 16:11

relate exponents to CIECAM02

Diffstat

1 files changed, 10 insertions, 2 deletions

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

@@ -90,8 +90,7 @@ perceived measure `J` can be expressed as `J = a * log(Y) + b`. This is called
   90    90 the Weber-Fechner law.
   91    91 
   92    92 In 1961 Stevens published a different model that was found to more accurately
   93    -1 predict human vision. It has the form `J = a * pow(Y, alpha) + b`. The exponent
   94    -1 `alpha` has a value of approximately 1/3.[^1]
   -1    93 predict human vision. It has the form `J = a * pow(Y, alpha) + b`.[^1]
   95    94 
   96    95 ### WCAG 2.x
   97    96 
@@ -335,6 +334,15 @@ value in WCAG 2.x to 0.4 we would get results much closer to APCA. And if we
  335   334 were to change the exponents in APCA to 1/3 we would get results much closer to
  336   335 WCAG 2.x.
  337   336 
   -1   337 The most complete (but also most complex) color appearance model currently
   -1   338 available is [CIECAM02](https://en.wikipedia.org/wiki/CIECAM02). Its definition
   -1   339 of lightness can be approximated as `100 * pow(Y, 0.42 * c * z)`, where `c` and
   -1   340 `z` are parameters that depend on the lighting conditions.  The total exponent
   -1   341 can have values between 0.31 and 0.72.
   -1   342 
   -1   343 Given that model, WCAG 2.x is on the lower (darker) end of possible exponents,
   -1   344 while APCA goes to the other (lighter) extreme.
   -1   345 
  338   346 ## Spatial frequency
  339   347 
  340   348 Smaller text is generally harder to read than bigger text. In a more general