Merge commit '9b0050e9aabe4be65c78ccf292a348f309d50ccd' as 'docs'

```
git subtree add --prefix=docs/ https://github.com/gohugoio/hugoDocs.git master --squash
```

Closes #11925

docs/content/en/functions/images/UnsharpMask.md

@@ -0,0 +1,40 @@
+---
+title: images.UnsharpMask
+description: Returns an image filter that sharpens an image.
+categories: []
+keywords: []
+action:
+  aliases: []
+  related:
+    - functions/images/Filter
+    - methods/resource/Filter
+  returnType: images.filter
+  signatures: [images.UnsharpMask SIGMA AMOUNT THRESHOLD]
+toc: true
+---
+
+The sigma parameter is used in a gaussian function and affects the radius of effect. Sigma must be positive. The sharpen radius is approximately 3 times the sigma value.
+
+The amount parameter controls how much darker and how much lighter the edge borders become. Typically between 0.5 and 1.5.
+
+The threshold parameter controls the minimum brightness change that will be sharpened. Typically between 0 and 0.05.
+
+## Usage
+
+Create the filter:
+
+```go-html-template
+{{ $filter := images.UnsharpMask 10 0.4 0.03 }}
+```
+
+{{% include "functions/images/_common/apply-image-filter.md" %}}
+
+## Example
+
+{{< img
+  src="images/examples/zion-national-park.jpg"
+  alt="Zion National Park"
+  filter="UnsharpMask"
+  filterArgs="10,0.4,0.03"
+  example=true
+>}}