Apply a Filter to a Background Image

You can apply a filter to an entire element quite easily with the filter property. But what if you want to apply a filter just to the background of an element? It’s weirdly tricky.

There are CSS properties that specific to backgrounds, like background-blend-mode — but blending and filters are not the same thing. It sorta seems to be the reason we have backdrop-filter, but not quite. That does filtering as the background interacts with what is behind the element.

There is no background-filter, unfortunately. What are we to do?

Use a pseudo-element instead of a background

If you put the contents of the element in an inside wrapper, you can set that on top of a pseudo-element that is simply pretending to be a background.

.module { position: relative;
}
.module::before { content: ""; position: absolute; top: 0; left: 0; width: 100%; height: 100%; background-image: url(graphic-to-be-filtered.jpg); filter: grayscale(100%);
}
.module-inside { /* This will make it stack on top of the ::before */ position: relative;
}

See the Pen Apply Filter to Psuedo Element by Chris Coyier (@chriscoyier) on CodePen.

See how the “background” gets filtered with grayscale there? We called the grayscale filter there and applied it only to the pseudo-element, leaving the rest of the content inside unfiltered.

It depends on what kind of filtering you want… you might be able to fake it with blend modes

I ran into this issue as I was specifically trying to grayscale the background image of an element. Since, as we’ve covered, there is no specific property just for that, I thought about background-blend-mode, particularly how there are blending options for things like saturation and color. If I could set pure black over the top of the graphic, then I could blend them — like I can with multiple backgrounds — and essentially fake a grayscale effect.

Note that you can’t use a solid color by itself when working with multiple backgrounds (that would be a background-color not background-image), so we have to fake that as well with a no-transition linear-gradient.

.module { background-image: linear-gradient(black, black), url(image-to-be-fake-filters.jpg); background-size: cover; background-blend-mode: saturation;
}

See the Pen Apply Fake Filter with Blend Mode by Chris Coyier (@chriscoyier) on CodePen.

Dan Wilson’s explorations

Dan got way into this and made an exploratory Pen in which there are three layers:

  1. Top layer: a vignette from a radial-gradient
  2. Middle layer: solid color
  3. Bottom layer: image graphic

You can adjust the colors used on the top two layers and apply different blend modes to each one. That was another thing I learned! Just like you can comma-separate to make multiple backgrounds (and likewise with background-size, background-position and such to apply those values to specific backgrounds) you can also comma-separate background-blend-mode to apply different blending effects to each layer.

See the Pen Multiple Backgrounds, Multiple Blend Modes by Dan Wilson (@danwilson) on CodePen.

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Netlify

(This is a sponsored post.)

It’s always fun to watch developers discover Netlify for the first time. It’s so easy. One way to do it is to just literally drag and drop a folder onto them and it will be online. Even better, connect a Git repo to a Netlify site and tell it what branch you want to watch, then any commits to that branch will automatically go live, even running your site’s build as it does it. I heard one developer say, “It’s like someone actually designed hosting and deployment.”

That lends itself nicely to static sites, but don’t think that static sites are only for certain types of sites or limiting in some way. That’s what the JAMstack is all about! Wanna learn more about that? Come to JAMstack_conf!

Netlify does a ton to help you power your JAMstack site as well. They’ll process your forms. They’ll help you with authentication. They’ll do your A/B testing. They’ll even run your cloud functions. Pretty incredible, really.

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