apca-introduction

commit

ba30c425ab709c9bb382b970b204ed3c9a547b35

parent

a766058ea9e559c64a38512d64e4778287037f06

Author

Tobias Bengfort <tobias.bengfort@posteo.de>

Date

2022-08-07 11:06

add some sources

Diffstat

1 files changed, 7 insertions, 3 deletions

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

@@ -91,7 +91,7 @@ the Weber-Fechner law.
   91    91 
   92    92 In 1961 Stevens published a different model that was found to more accurately
   93    93 predict human vision. It has the form `L = a * pow(Y, alpha) + b`. The exponent
   94    -1 `alpha` has a value of approximately 1/3.
   -1    94 `alpha` has a value of approximately 1/3.[^1]
   95    95 
   96    96 ### WCAG 2.x
   97    97 
@@ -135,7 +135,7 @@ a much bigger response than the same amount of blue light.
  135   135 Next, 0.05 is added to both values to account for ambient light that is
  136   136 reflected on the screen (flare). Since we are in the domain of physical light,
  137   137 we can just add these values. 0.05 mean that we assume that the flare amounts
  138    -1 to 5% of the white of the screen.
   -1   138 to 5% of the white of the screen.[^2]
  139   139 
  140   140 Then the Weber contrast is calculated. Note that `(Y1 - Y2) / Y2` is the same
  141   141 as `Y1 / Y2 - 1`. The shift by 1 is removed because it has no impact on the
@@ -351,7 +351,7 @@ color contrast is needed.
  351   351 There is one caveat though: The spatial frequency only defines the contrast
  352   352 threshold under which a pattern is not perceivable at all. Above that it has
  353   353 barely any effect. So we the best way to use it is to define a minimum required
  354    -1 color contrast based on spatial frequency.
   -1   354 color contrast based on spatial frequency.[^3]
  355   355 
  356   356 Interestingly, a lower spatial frequency is not always easier to read though.
  357   357 [Studies have shown] that the optimal spatial frequency is at about 5-7 cycles
@@ -561,3 +561,7 @@ figuring out what questions need to be answered.
  561   561 [does attempt to model spatial frequency]: https://git.apcacontrast.com/WEBTOOLS/APCA/
  562   562 [1.4.11]: https://www.w3.org/TR/WCAG21/#non-text-contrast
  563   563 [lack of publicly available evidence]: https://github.com/w3c/silver/issues/574
   -1   564 
   -1   565 [^1]: [Monaci, Gianluca & Menegaz, Gloria & Susstrunk, S. & Knoblauch, Kenneth. (2022). Color Contrast Detection in Spatial Chromatic Noise.](https://www.researchgate.net/publication/37435854_Color_Contrast_Detection_in_Spatial_Chromatic_Noise)
   -1   566 [^2]: [Hwang AD, Peli E. (2016). New Contrast Metric for Realistic Display Performance Measure.](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5489230/)
   -1   567 [^3]: [Georgeson, M. A., & Sullivan, G. D. (1975). Contrast constancy: deblurring in human vision by spatial frequency channels.](https://pubmed.ncbi.nlm.nih.gov/1206570/)