Lena Söderberg full colorLena Söderberg desaturated with CSS

The CSS greyscale filter

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

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

Chrome and Safari still implement CSS filters with vendor prefixes, so we need to add a declaration for those:

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

The CSS greyscale filter

Desaturating a color image couldn’t be simpler with CSS. 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%);
}

(Note the spelling of “grayscale”; the alternative spelling will not work)

Some browsers implement CSS filters via vendor prefixes, so our first job is to insert the final unprefixed code, preceded by another declaration to fulfill the needs of Webkit-based browsers:

img.desaturate { 
	-webkit-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 in Chrome 18+, Safari 6 and higher on both mobile and desktop platforms, Firefox 35+, Opera 15+, and the latest browser versions for Android and Blackberry; IE support is in development.

To gain the same effect in earlier versions of Firefox, 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 HTML page and test image, the CSS is extended to become:

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

Add Support for IE

To cover IE 6 – 9, we'll apply Microsoft’s simple but proprietary use of filter:

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

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

img.desaturate{
	-webkit-filter: grayscale(1);
	-webkit-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.

A slightly easier approach for older versions of Firefox 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");
}