How for entered color calculate background color?

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In my @vue/cli 4.1.1 app user enter color and I have to output color value with entered color and I wonder how can I calculate and set background color to be sure that entered color value is good visible. I mean if user entered white color(or near) background must be dark?

Thanks

rgb javascript
2 Answers

You can determine the entered color to be light or dark on the basis of its luminance.

Here you can find a formula it's calculated on.

So, you can, for example, define the function isLight like this

function isLight(color) {
  // Converting hex color to rgb
  const [red, green, blue] = hexToRgb(color);

  // Determine luminance
  const luminance = (0.299 * red + 0.587 * green + 0.114 * blue)/255;

  // Returning true if color is light
  return luminance > 0.5;
}

// function for converting hex colors to rgb array format
function hexToRgb(hex) {
  const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
  return result ? [
    parseInt(result[1], 16),
    parseInt(result[2], 16),
    parseInt(result[3], 16)
  ] : null;
}

By using this function you can determine if the user color is light or dark and thus set the appropriate background

user_48964930

You can give an invert color - 255-color for each of rgb

function bg(r, g, b) {return [255-r, 255-g, 255-b]}

if you get it in hex format, you can convert it to rgb, then get the invert. like so:

function invert(hex){
  hex = parseInt(hex.substring(1), 16);
  var r = hex >> 16;
  hex -= r << 16;
  var g = hex >> 8;
  hex -= g << 8;
  var b = hex;
  return `rgb(${255-r},${255-g},${255-b})`;
}
var color1 = "#eeff00";
var color2 = "#22faef";
var color3 = "#f1f1f1";
document.querySelector('#a').style = `color:${color1};background-color:${invert(color1)}`;
document.querySelector('#b').style = `color:${color2};background-color:${invert(color2)}`;
document.querySelector('#c').style = `color:${color3};background-color:${invert(color3)}`;
div {
padding: 10px;
}
<div id="a">Hello world!</div>
<div id="b">Hello world!</div>
<div id="c">Hello world!</div>

user_85087770
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