first commit

auto_contrast.js

@@ -0,0 +1,34 @@
+import {calcAPCA} from './apca-w3.js';
+import { formatHex, converter} from './culori.mjs';
+import {nearestNamedColors} from './color-picker.js';
+
+export function find_contrast(col_a, col_b, target_contrast=90, num_close_colours=1, temp=0.1) {
+  const [bname] = nearestNamedColors(col_b,1);
+  let tcol_b = col_b;
+  function score(c) {
+    return Math.abs(c - target_contrast);
+  }
+  for(let j=0;j<30;j++) {
+    const possibles = [];
+    for(let i =0; i<50; i++) {
+      const {l, a, b} = tcol_b;
+      const [nl, na, nb] = [l,a,b].map(x=>x+(Math.random()*2-1)*temp);
+      const ncol = {mode: 'oklab', l: nl, a: na, b: nb};
+      const names = nearestNamedColors(culori.oklab(formatHex(ncol)),num_close_colours);
+      if(!names.some(name => name==bname)) {
+        continue;
+      }
+      const contrast = Math.abs(calcAPCA(formatHex(col_a), formatHex(ncol)));
+      possibles.push({ncol, contrast});
+    }
+    if(possibles.length==0) {
+      continue;
+    }
+    const [best] = possibles.sort((a,b) => {const ca = score(a.contrast); const cb = score(b.contrast); return ca<cb ? -1 : 1});
+    tcol_b = best.ncol;
+    temp *= 0.9; 
+  }
+  const [{name}] = nearestNamedColors(tcol_b,1);
+  return tcol_b;
+}
+