Change text color based on brightness of the covered background area?

Question

I am looking for a plugin or technique that changes a text's color or switches between predefined images/icons depending on the average brightness of the covered pixels of its parent's background-image or -color.

If the covered area of it's background is rather dark, make the text white or switch the icons.

Additionally, it'd be great if the script would notice if the parent has no defined background-color or -image and then continue to search for the nearest (from parent element to its parent element..).

What do you think, know about this idea? Is there something similar out there already? Examples?

Solution 1

Interesting resources for this:

• W3C - Ensure that foreground and background color combinations provide sufficient contrast
• Calculating the Perceived Brightness of a Color

Here's the W3C algorithm (with JSFiddle demo too):

const rgb = [255, 0, 0];

// Randomly change to showcase updates
setInterval(setContrast, 1000);

function setContrast() {
  // Randomly update colours
  rgb[0] = Math.round(Math.random() * 255);
  rgb[1] = Math.round(Math.random() * 255);
  rgb[2] = Math.round(Math.random() * 255);

  // http://www.w3.org/TR/AERT#color-contrast
  const brightness = Math.round(((parseInt(rgb[0]) * 299) +
                      (parseInt(rgb[1]) * 587) +
                      (parseInt(rgb[2]) * 114)) / 1000);
  const textColour = (brightness > 125) ? 'black' : 'white';
  const backgroundColour = 'rgb(' + rgb[0] + ',' + rgb[1] + ',' + rgb[2] + ')';
  $('#bg').css('color', textColour); 
  $('#bg').css('background-color', backgroundColour);
}

#bg {
  width: 200px;
  height: 50px;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<div id="bg">Text Example</div>

Solution 2

This article on 24 ways about Calculating Color Contrast might be of interest to you. Ignore the first set of functions because they're wrong, but the YIQ formula will help you determine whether or not to use a light or dark foreground color.

Once you obtain the element's (or ancestor's) background color, you can use this function from the article to determine a suitable foreground color:

function getContrastYIQ(hexcolor){
    hexcolor = hexcolor.replace("#", "");
    var r = parseInt(hexcolor.substr(0,2),16);
    var g = parseInt(hexcolor.substr(2,2),16);
    var b = parseInt(hexcolor.substr(4,2),16);
    var yiq = ((r*299)+(g*587)+(b*114))/1000;
    return (yiq >= 128) ? 'black' : 'white';
}

Solution 3

mix-blend-mode does the trick:

header {
  overflow: hidden;
  height: 100vh;
  background: url(https://www.w3schools.com/html/pic_mountain.jpg) 50%/cover;
}

h2 {
  color: white;
  font: 900 35vmin/50vh arial;
  text-align: center;
  mix-blend-mode: difference;
  filter: drop-shadow(0.05em 0.05em orange);
}

<header>
  <h2 contentEditable role='textbox' aria-multiline='true' >Edit me here</h2>
</header>

Addition (March 2018): Following, a nice tutorial explaining all different types of modes/implementations: https://css-tricks.com/css-techniques-and-effects-for-knockout-text/

Solution 4

Interesting question. My immediate thought was to invert the color of the background as the text. This involves simply parsing the background and inverting its RGB value.

Something like this: http://jsfiddle.net/2VTnZ/2/

var rgb = $('#test').css('backgroundColor');
var colors = rgb.match(/^rgb\((\d+),\s*(\d+),\s*(\d+)\)$/);
var brightness = 1;

var r = colors[1];
var g = colors[2];
var b = colors[3];

var ir = Math.floor((255-r)*brightness);
var ig = Math.floor((255-g)*brightness);
var ib = Math.floor((255-b)*brightness);

$('#test').css('color', 'rgb('+ir+','+ig+','+ib+')');

Solution 5

I've found the BackgroundCheck script to be very useful.

It detects the overal brightness of the background (be it a background image or a color), and applies a class to the assigned text-element (background--light or background--dark), dependent on the brightness of the background.

It can be applied to still and moving elements.

(Source)

View more solutions

Comments

[jackwanders]

You'd probably want to desaturate your 'inverted' color by averaging the inverted R,G,B values and setting them equal to each other. However, this solution is getting its base color from a string, and not from the CSS property of the element. To be reliable, the solution would have to dynamically obtain background colors, which usually returns rgb() or rgba() values, but could differ according to browser.

[jeremyharris]

Yes. For ease of parsing, I just used a hex value. I updated the fiddle to include grabbing the element's color from the CSS. I updated the fiddle and included a sort of brightness control (I don't know anything about color math so it's probably not truly brightness).

[James Cazzetta]

Thanks, this is really helpful.. This depends on the set background-color.. But do you know how to get the average color of an image by running through each pixel (like in a loop)?

[James Cazzetta]

@jeremyharris This is a very helpful piece of code, but to extend the possibilities, do you know how to get the average color of an image by running through each pixel (like in a loop)? So, instead of grabbing the background-color via CSS we could gain the background-images average color.

[jeremyharris]

How about this? stackoverflow.com/questions/2541481/…

[Nathan MacInnes]

What if the background colour is #808080!?

[jeremyharris]

@NathanMacInnes it'll still invert it, it just so happens that inverting something right in the middle of the spectrum will result in itself. This code just inverts the color, which comes with its limitations.

[reggie]

What if the text does not have a background color, but its parent element?

[Centril]

In es6 you can do this with: const getContrastYIQ = hc => { const [r, g, b] = [0, 2, 4].map( p => parseInt( hc.substr( p, 2 ), 16 ) ); return ((r * 299) + (g * 587) + (b * 114)) / 1000 >= 128; }

[Jørgen Skår Fischer]

Does this work for background-colors? I've fast-read the script, and cant see it utilizing background-color to check for brightness. Only images.

[cptstarling]

Hello Jørgen, I think the colourBrightness script may serve your purpose: github.com/jamiebrittain/colourBrightness.js

[Hanna]

I took this function and expanded it a bit so that you could return two custom colors, rather than always black and white. Note that if the colors are two close together you may still get contrast issues, but this is a good alternative to returning absolute colors jsfiddle.net/1905occv/1

[Petroff]

@reggie it's your job to do correct selector to select color and is not related to the question.

[Luke Robertson]

Can be shorted to the following, providing you pass it a object :::: const setContrast = rgb => (rgb.r * 299 + rgb.g * 587 + rgb.b * 114) / 1000 > 125 ? 'black' : 'white'

[Arturo]

this one is coo, I would just adjust the yiq to >= 160, worked better for me.

[B''H Bi'ezras -- Boruch Hashem]

do u rly need jquery just for changing the css?

[Alex Ball]

@bluejayke no, there are other ways ;-)