Filtering in CSS is a useful method for modifying the rendering of an HTML element and its children. This could include applying effects such as blurring, adjusting brightness, or converting the image to grayscale. You use the filter property in your CSS to apply filters to your elements.
Follow this general syntax to filter in CSS:
```
selector {
filter: function(value);
}
```
The function can be any of these filter functions:
`blur()`: Applies a blur effect to the element. You define the strength of the blurring in pixels within the parentheses.
`brightness()`: Changes the brightness of the element. You define the level of brightness within the parentheses, where 0 is completely dark and 1 is the original color.
`contrast()`: Changes the contrast of the element. Like brightness, values range between 0 and 1.
`saturate()`: Saturates the element. A value of 0 is completely unsaturated, while a value of 1 represents the original color.
`grayscale()`: Converts the element to grayscale. A value of 0 represents the original color, and a value of 1 represents complete grayscale.
`hue-rotate()`: Applies a hue rotation on the image. The value inside the parentheses represents degrees.
`invert()`: Inverts the colors of the element. A value of 0 is the original color, and a value of 1 is completely inverted.
`opacity()`: Changes the opacity of the element. A value of 0 is completely transparent, and a value of 1 is the original color.
`sepia()`: Converts the element to sepia. A value of 0 is the original color, and a value of 1 is complete sepia.
`drop-shadow()`: Applies a drop shadow effect to the image. The function accepts the h-shadow, v-shadow, blur, spread, and color properties in this order.
You can combine multiple filter functions, separated by spaces.
Example:
```
img {
filter: grayscale(0.5) brightness(0.5);
}
```
In the above example, the image will be converted to 50% grayscale and 50% of its original brightness.
