The `filter()` function

[thebabydino]

Description

This allows us to apply a filter to an image before it's used as a background-image or border-image.

It has been in Safari for almost a decade now, but no other browser has followed. Basic test.

• Chrome 🪲 541698
• Firefox 🪲 1191043

Even in Safari, it doesn't work for CSS gradients - 🪲 250303.

Sometimes we only want to apply a filter on an element's background-image or border-image-source, but not to the entire element.

For example, we may want to make a background-image semitransparent. With filter(), this is as simple as:

.my-elem {
    background: filter(url(balloon.jpg), opacity(.5)) 50%/ cover
}

Live demo (Safari only).

Otherwise, we have to create an absolutely positioned pseudo-element that covers its entire parent, move it behind any text content we may have. Finally we need to make the pseudo-element semitransparent. More code, plus we're using up a pseudo-element that we might need for something else.

.my-elem {
    position: relative
}

.my-elem::before {
    position: absolute;
    inset: 0;
    z-index: -1;
    background: url(balloon.jpg) 50%/ cover;
    opacity: .5;
    content: ''
}

Similarly, we may want to selectively desaturate a background-image. That is, considering our background-image is one with red roses we want an effect like that of the grayscale filter on everything but the red of the rose petals. Again, this is one line of CSS with filter() (live demo, Safari only), but we need to resort to a pseudo otherwise.

Things get a bit more complicated when we want that pseudo to have a filtered image background layer which then gets blended with another background layer of the same pseudo and finally, the whole pseudo itself has a filter applied. This is the case if, starting from a random image, we want to turn it into its grayscale halftone dots version.

Live demo, Safari only. Without filter(), we'd need an extra element to achieve the same result.

Another situation is when we only want to a apply a filter to the border-image-source. For example, let's say we want the spaced out (with a padding area gap) border of an image to be a gradient that seems extracted out of the image palette. img elements can't have ::before/ ::after pseudos, so a no filter() solution would involve a wrapper. With filter(), we can do this by applying a large blur on the border-image-source and then an alpha correction. Live demo, Safari only.

Specification

Filter Effects Module Level 1

Additional Signals

No response