apca-introduction

commit

aad047023ae4b47bb3f091a8a8ffdb4974f93deb

parent

5a2f7c7b387de65a01851fb47286d19ab915636f

Author

Tobias Bengfort <tobias.bengfort@posteo.de>

Date

2022-08-19 17:28

mention APCA flare value

Diffstat

3 files changed, 5 insertions, 4 deletions

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

@@ -188,7 +188,8 @@ The conversion from sRGB to luminance uses similar coefficients, but the
  188   188 non-linear part is very different. The author of APCA provides some motivation
  189   189 for these changes in the article [Regarding APCA Exponents]. The main argument
  190   190 seems to be that this is supposed to more closely model real-world computer
  191    -1 screens. This document also explains that this step incorporates flare.
   -1   191 screens. This step also incorporates a flare of `Math.pow(0.022, 1.414) ~=
   -1   192 0.0045`.
  192   193 
  193   194 Next, the contrast is calculated based on the Stevens model. Interestingly,
  194   195 APCA uses four different exponents for light foreground (0.62), dark foreground
@@ -326,7 +327,7 @@ I plotted curves for both the Weber-Fechner model (log) and the Stevens model
  326   327 -   The log curve with a flare of 0.05 (WCAG 2) is closer to the pow curve with
  327   328     an exponent of 1/3 and a flare of 0.0025
  328   329 -   The log curve with a flare of 0.4 is closer to the pow curves with
  329    -1     exponents 0.56 and 0.68 (similar to APCA)
   -1   330     exponents 0.56 and 0.68 and a flare of 0.0045 (similar to APCA)
  330   331 
  331   332 This shows that a big part of the different results between WCAG 2.x and APCA
  332   333 are caused by a different choice in parameters. If we were to change the flare

diff --git a/plots/lightness_comparison.png b/plots/lightness_comparison.png

diff --git a/plots/lightness_comparison.py b/plots/lightness_comparison.py

@@ -24,8 +24,8 @@ if __name__ == '__main__':
   24    24 	weber(0.05)
   25    25 	weber(0.4)
   26    26 	stevens(0.0025, 0.333)
   27    -1 	stevens(0, 0.56)
   28    -1 	stevens(0, 0.68)
   -1    27 	stevens(0.0045, 0.56)
   -1    28 	stevens(0.0045, 0.68)
   29    29 
   30    30 	plt.legend(legend)
   31    31 	plt.savefig('lightness_comparison.png')