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Lena Söderberg full colorLena Söderberg desaturated with CSS

Convert Images To Black And White With CSS

css / filters

Estimated reading time: 2 minutes, 37 seconds

Filters allow us to visually process an image in the browser without needing to go through or use cycle-intensive, script-heavy methods in or PHP. are broadly supported in the most recent versions of Firefox, Safari and Chrome, and we can gain support in older versions and alternative browsers – even IE –  by using a combination of techniques.

In this article we’ll convert an image to black & white with pure CSS using the classic test image of Lena Söderberg. In other articles in this series I discuss how to achieve sepia toning, blurring, and other visual effects.

The CSS3 greyscale filter

Desaturating a color image couldn’t be simpler with CSS3. We’ll apply the filter as a class, as you’d typically desire several images to be affected by the code at the same time:

img.desaturate { filter: grayscale(100%); }

Naturally, all current browsers implement CSS3 filters via vendor prefixes, so our first job is to insert that code, writing in CSS that does not yet exist in order to future-proof our work:

img.desaturate { -webkit-filter: grayscale(100%);
-moz-filter: grayscale(100%);
filter: grayscale(100%);
}

Applying the class to the image is easy:

<img src="lena-söderberg.png" alt="Lena Söderberg" style="width: 512px; height: 512px;" class="desaturate">

Add An SVG Filter Effect

The CSS shown to this point works only in Chrome 18+, with support in other browsers expected to arrive soon. To gain the same effect in Firefox 4+, we need to use an filter, which I’ll create as a separate document named desaturate.svg. The code for that file will be:

<svg version="1.1" xmlns="http://www.w3.org/2000/svg">
<filter id="greyscale">
<feColorMatrix type="matrix" values="0.3333 0.3333 0.3333 0 0
 0.3333 0.3333 0.3333 0 0
 0.3333 0.3333 0.3333 0 0
 0  0  0  1 0" />
 </filter>
 </svg>

If the SVG code looks slightly daunting – and the matrix math behind it is somewhat complex – don’t worry. This is one piece of code that I’d actually encourage you to copy and paste as a generic “recipe”. I’ll explain matrix transformations in a future article.

With the SVG file saved beside our page and test image, we will extend the CSS to become:

img.desaturate{
-webkit-filter: grayscale(100%); -moz-filter: grayscale(100%);
filter: grayscale(100%);
filter: url(desaturate.svg#greyscale);
}

Add Support for IE

So far our code covers future browsers, recent versions of Chrome and Firefox 4+. To include IE 6 – 9, we'll apply Microsoft’s simple but proprietary use of filter:

img.desaturate{
-webkit-filter: grayscale(100%); -moz-filter: grayscale(100%);
filter: gray; filter: grayscale(100%);
filter: url(desaturate.svg#greyscale);
}

If you want to add in support for older versions of Webkit:

img.desaturate{
-webkit-filter: grayscale(1); -webkit-filter: grayscale(100%); -moz-filter: grayscale(100%);
filter: gray; filter: grayscale(100%);
filter: url(desaturate.svg#greyscale);
}

The CSS we've written here allows us to visually convert an image to black and white on the fly in our browser, with no need to save new versions in PhotoShop. Using CSS also makes the image much easier to modify: for example, you’ll see that lowering the percentage used in our declaration from 100% to 50% causes a visual blend of the desaturation effect with the original color image.

Update

A slightly easier approach inlines the SVG into the CSS directly, removing the need for any SVG code in the <body>:

img.desaturate{
-webkit-filter: grayscale(100%);
filter: grayscale(100%);
filter: gray;
filter: url("data:image/svg+xml;utf8,<svg version='1.1' xmlns='http://www.w3.org/2000/svg' height='0'><filter id='greyscale'><feColorMatrix type='matrix' values='0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0' /></filter></svg>#greyscale");
}
Play with this code on CodePen
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