A program to check WCAG contrast rules for foreground/background colors.
I've had this in my home toolbox for years, but recently needed this on another machine, so I'm making it available so I can find it again.
At its simplest, you can pass a FOREGROUND and a BACKGROUND color, in hex notation, and it'll output information about the contrast for the two:
$ ./contrast ff0000 111112
fg ff0000 hsl(0°, 100%, 50%)
on 111112 hsl(240°, 2%, 6%)
= EXAMPLE
= 4.720:1 contrast
✔PASS AA large
✘FAIL AAA large
✘FAIL AA text
✘FAIL AAA textThe "EXAMPLE" text is suitably ANSI colored, using \e[38;2;R;G;Bm for the
foreground color, and \e[48;2;R;G;Bm for the background color.
If given the -l option (which must come after the FOREGROUND and BACKGROUND
values), it outputs all the information in one line:
$ ./contrast ff0000 111112 -l
fg ff0000 hsl(0°, 100%, 50%) on 111112 hsl(240°, 2%, 6%) = EXAMPLE = 4.720:1 contrast ✔PASS AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA textThis makes it easy/possible to use it for gauging which colors of a whole palette can be used with each other without failing any WCAG specification, i.e.:
$ export PALETTE='ff0000 eeeeee 000000 111111'
$ for fg in $PALETTE; do for bg in $PALETTE; do ./contrast "$fg" "$bg" -l ; done ; done
fg ff0000 hsl(0°, 100%, 50%) on ff0000 hsl(0°, 100%, 50%) = EXAMPLE = 1.000:1 contrast ✘FAIL AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA text
fg ff0000 hsl(0°, 100%, 50%) on eeeeee hsl(0°, 0%, 93%) = EXAMPLE = 3.446:1 contrast ✔PASS AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA text
fg ff0000 hsl(0°, 100%, 50%) on 000000 hsl(0°, 0%, 0%) = EXAMPLE = 5.252:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✘FAIL AAA text
fg ff0000 hsl(0°, 100%, 50%) on 111111 hsl(0°, 0%, 6%) = EXAMPLE = 4.723:1 contrast ✔PASS AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA text
fg eeeeee hsl(0°, 0%, 93%) on ff0000 hsl(0°, 100%, 50%) = EXAMPLE = 3.446:1 contrast ✔PASS AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA text
fg eeeeee hsl(0°, 0%, 93%) on eeeeee hsl(0°, 0%, 93%) = EXAMPLE = 1.000:1 contrast ✘FAIL AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA text
fg eeeeee hsl(0°, 0%, 93%) on 000000 hsl(0°, 0%, 0%) = EXAMPLE = 18.100:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✔PASS AAA text
fg eeeeee hsl(0°, 0%, 93%) on 111111 hsl(0°, 0%, 6%) = EXAMPLE = 16.275:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✔PASS AAA text
fg 000000 hsl(0°, 0%, 0%) on ff0000 hsl(0°, 100%, 50%) = EXAMPLE = 5.252:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✘FAIL AAA text
fg 000000 hsl(0°, 0%, 0%) on eeeeee hsl(0°, 0%, 93%) = EXAMPLE = 18.100:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✔PASS AAA text
fg 000000 hsl(0°, 0%, 0%) on 000000 hsl(0°, 0%, 0%) = EXAMPLE = 1.000:1 contrast ✘FAIL AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA text
fg 000000 hsl(0°, 0%, 0%) on 111111 hsl(0°, 0%, 6%) = EXAMPLE = 1.112:1 contrast ✘FAIL AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA text
fg 111111 hsl(0°, 0%, 6%) on ff0000 hsl(0°, 100%, 50%) = EXAMPLE = 4.723:1 contrast ✔PASS AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA text
fg 111111 hsl(0°, 0%, 6%) on eeeeee hsl(0°, 0%, 93%) = EXAMPLE = 16.275:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✔PASS AAA text
fg 111111 hsl(0°, 0%, 6%) on 000000 hsl(0°, 0%, 0%) = EXAMPLE = 1.112:1 contrast ✘FAIL AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA text
fg 111111 hsl(0°, 0%, 6%) on 111111 hsl(0°, 0%, 6%) = EXAMPLE = 1.000:1 contrast ✘FAIL AA large ✘FAIL AAA large ✘FAIL AA text ✘FAIL AAA textThis is particularly much easier to use with a | grep -v FAIL at the end, to
show only combinations of foreground/background which don't fail WCAG, i.e.:
$ for fg in $PALETTE; do for bg in $PALETTE; do ./contrast "$fg" "$bg" -l ; done ; done | grep -v FAIL
fg eeeeee hsl(0°, 0%, 93%) on 000000 hsl(0°, 0%, 0%) = EXAMPLE = 18.100:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✔PASS AAA text
fg eeeeee hsl(0°, 0%, 93%) on 111111 hsl(0°, 0%, 6%) = EXAMPLE = 16.275:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✔PASS AAA text
fg 000000 hsl(0°, 0%, 0%) on eeeeee hsl(0°, 0%, 93%) = EXAMPLE = 18.100:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✔PASS AAA text
fg 111111 hsl(0°, 0%, 6%) on eeeeee hsl(0°, 0%, 93%) = EXAMPLE = 16.275:1 contrast ✔PASS AA large ✔PASS AAA large ✔PASS AA text ✔PASS AAA textCopyright 2023 Marco Fontani MFONTANI@cpan.org
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