apca-introduction

commit

3cb0bc7270de561799d6588384b5955d6f289087

parent

5ba42ff5d2aeeec02a2d4c98ddd0626e092c718a

Author

Tobias Bengfort <tobias.bengfort@posteo.de>

Date

2022-07-20 07:16

compare APCA to itself with inverted fg/bg

Diffstat

2 files changed, 23 insertions, 1 deletions

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

@@ -419,6 +419,23 @@ the APCA thresholds. As expected, most color pairs fall into the same category
  419   419 with both formulas. For example, only 1.7 % pass the modified WCAG 2.x with a
  420   420 contrast above 3.8, but fail APCA with a contrast below 45.
  421   421 
   -1   422 |        |  < 15 | 15-30 | 30-45 | 45-60 | 60-75 | 75-90 |  > 90 | total |
   -1   423 | ------:| -----:| -----:| -----:| -----:| -----:| -----:| -----:| -----:|
   -1   424 |   < 15 |  33.6 |   1.3 |   0.0 |   0.0 |   0.0 |   0.0 |   0.0 |  34.9 |
   -1   425 |  15-30 |   1.3 |  23.1 |   1.3 |   0.0 |   0.0 |   0.0 |   0.0 |  25.7 |
   -1   426 |  30-45 |   0.0 |   1.4 |  16.5 |   1.1 |   0.0 |   0.0 |   0.0 |  18.9 |
   -1   427 |  45-60 |   0.0 |   0.0 |   1.2 |  10.4 |   0.7 |   0.0 |   0.0 |  12.3 |
   -1   428 |  60-75 |   0.0 |   0.0 |   0.0 |   0.8 |   5.2 |   0.3 |   0.0 |   6.2 |
   -1   429 |  75-90 |   0.0 |   0.0 |   0.0 |   0.0 |   0.3 |   1.5 |   0.0 |   1.8 |
   -1   430 |   > 90 |   0.0 |   0.0 |   0.0 |   0.0 |   0.0 |   0.0 |   0.1 |   0.1 |
   -1   431 |  total |  34.9 |  25.8 |  18.9 |  12.3 |   6.2 |   1.8 |   0.1 |       |
   -1   432 
   -1   433 The third table compares APCA to itself, but with foreground and background
   -1   434 switched. WCAG 2.x does not make a difference between foreground and
   -1   435 background, so this comparison would be pointless there. APCA on the other hand
   -1   436 uses different exponents for foreground and background. This table shows that
   -1   437 this does have a small but still significant impact on the results.
   -1   438 
  422   439 ## Conclusion
  423   440 
  424   441 In this analysis I took a deeper look at the Accessible Perceptual Contrast

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

@@ -76,13 +76,18 @@ if __name__ == '__main__':
   76    76 	apca_yfg = apca_y(fg)
   77    77 	apca_ybg = apca_y(bg)
   78    78 	apca = apca_contrast(apca_yfg, apca_ybg)
   -1    79 	apcai = apca_contrast(apca_ybg, apca_yfg)
   79    80 
   80    81 	wcag_yfg = wcag_y(fg)
   81    82 	wcag_ybg = wcag_y(bg)
   82    83 	wcag = wcag_contrast(wcag_yfg, wcag_ybg)
   83    84 	wcag4 = wcag_contrast(wcag_yfg, wcag_ybg, 0.4)
   84    85 
   85    -1 	for _wcag, wcag_levels in [(wcag, WCAG_LEVELS), (wcag4, WCAG4_LEVELS)]:
   -1    86 	for _wcag, wcag_levels in [
   -1    87 		(wcag, WCAG_LEVELS),
   -1    88 		(wcag4, WCAG4_LEVELS),
   -1    89 		(apcai, APCA_LEVELS),
   -1    90 	]:
   86    91 		rows = []
   87    92 		for wcag_lower, wcag_upper in iter_levels(wcag_levels):
   88    93 			rows.append([])