Gaussian Blur – SVG Filters – C# Code

SVG Filters

Aspose.SVG for .NET lets you open or create, edit an SVG document and make changes to its content. You can modify the document, including applying the many available filters to get the desired result. The Aspose.Svg.Filters namespace contains classes and interfaces related to filter effects in SVG specification. The SVGFEGaussianBlurElement class corresponds to a <feGaussianBlur> element to implement the Gaussian Blur effect.

In SVG, a filter defines by <filter> element, which sets within a <defs> element. It is never rendered itself and is conceptually described as the element that includes its children – filter primitives. The <filter> element has a set of attributes. Required attributes for filter primitive are x, y, width, height, and id. They set the area of the picture to which the filter will be applied. And the attribute id gives a unique identifier to an SVG element and identifies an element within an SVG document.

In this article, you will learn how to write SVG code to create a Gaussian Blur filter and consider detailed C# examples of using the SVGFEGaussianBlurElement class to apply the Gaussian Blur effect to SVG elements and bitmaps.

Gaussian Blur – SVG Code

Gaussian blur SVG filter is a type of filter that applies a blur effect to the content of an SVG element using a Gaussian distribution. This is one of the most used filters in SVG to create soft, smooth, and visually appealing effects. The <feGaussianBlur> filter creates a soft blur effect. The StdDeviation attribute specifies the number that characterizes the standard deviation for the blur operation. If two numbers are provided, the first number represents a standard deviation value along the x-axis of the coordinate system, and the second one – on the y-axis. Each filter requires a source image to process. Otherwise, the filter will have nothing to render and so not work. The input data of the filter primitive is specified in the in attribute. The default is in="SourceGraphic".

Here’s an example of applying a Gaussian blur SVG filter with various values of stdDeviation attribute to an SVG rectangle element:

<svg height="150" width="750" xmlns="http://www.w3.org/2000/svg">
    <defs>
        <filter id="f1" x="-20" y="-20" height="100" width="100">
            <feGaussianBlur in="SourceGraphic" stdDeviation="10" />
        </filter>
        <filter id="f2" x="-20" y="-20" height="100" width="100">
            <feGaussianBlur in="SourceGraphic" stdDeviation="10, 0" />
        </filter>
        <filter id="f3" x="-20" y="-20" height="100" width="100">
            <feGaussianBlur in="SourceGraphic" stdDeviation="0,10" />
        </filter>
		<filter id="f4" x="-20" y="-20" height="100" width="100">
            <feGaussianBlur in="SourceGraphic" stdDeviation="20" />
        </filter>
		<filter id="f5" x="-20" y="-20" height="100" width="100">
            <feGaussianBlur in="SourceGraphic" stdDeviation="5" />
        </filter>
    </defs>
    <g fill="#ffa500">
        <rect x="40" y="40" width="60" height="60" />
        <rect x="40" y="40" width="60" height="60" transform="translate(120)" filter="url(#f1)" />
        <rect x="40" y="40" width="60" height="60" transform="translate(240)" filter="url(#f2)" />
        <rect x="40" y="40" width="60" height="60" transform="translate(360)" filter="url(#f3)" />
		<rect x="40" y="40" width="60" height="60" transform="translate(480)" filter="url(#f4)" />
		<rect x="40" y="40" width="60" height="60" transform="translate(600)" filter="url(#f5)" />
    </g>
</svg>

As you see, the stdDeviation value controls the spread of the Gaussian distribution. A larger stdDeviation value results in more blur, while a smaller value creates a softer effect.

Note: The blur, added around a shape, often makes the output picture larger than the source one. We need to use negative numbers for x and y to avoid clipping the graphics added by the filter. In the example above, we use x="-20" and y="-20".

Gaussian Blur – C# code

In the previous SVG code example, we discussed in detail how to create a Gaussian blur filter, and now we know what elements and attributes to use. Let’s create the C# code to implement such a filter using Aspose.SVG for .NET API.

According to SVG syntax, the <filter> element should be located in a <defs> element, and the <feGaussianBlur> filter primitive is only inside the <filter> element. Therefore, to program SVG filters, you must create and nest the required elements correctly.

1. If you create an SVG document from scratch, use the SVGDocument() constructor to create an empty SVG document.
2. The RootElement property of the SVGDocument class points to the document’s root <svg> element.
3. Create a <rect> element, set the required attributes, and add it to the <svg> element.
   • Use the CreateElementNS(namespaceURI, qualifiedName) method of the SVGDocument class to create an instance of the SVGRectElement.
   • One option for setting the values of the attribute is to use the SetAttribute(name, value) method. Another way is to take SVG DOM dot-accessor methods using properties of the SVGAnimatedLength type, the static data for which can be set or read through the construction: element.X.BaseVal.Value.
   • Use the AppendChild() method to add the <rect> element to the <svg> element.
4. Similarly, create a <defs> element and add it to the <svg> element.
5. To create a <filter> element, use the same algorithm: Use the CreateElementNS() method to create an instance of the SVGFilterElement. Remember to set x, y, height, width, and id attributes using SetAttribute() method and add the <filter> to the <defs> element.
6. Create a <feGaussianBlur> element and set in and stdDeviation attributes. Then add it to the <filter> element.
   • Use the CreateElementNS() method to create an instance of the SVGFEGaussianBlurElement class.
   • To set the In1 attribute, use the property of the SVGAnimatedLength type, the static data for which can be set or read through the construction feGaussianBlurElement.In1.BaseVal = "SourceGraphic".
   • Use the StdDeviationX and StdDeviationY properties of the SVGFEGaussianBlurElement class to set the setDerivation attribute.
   • Call the AppendChild() method to add the <feGaussianBlur> to the <filter> element.
7. Call the Save() method to save the document to a local file specified by path.

using Aspose.Svg;
using System.IO;
using Aspose.Svg.Filters;
...

    // Set SVG Namespace Url
    string SvgNamespace = "http://www.w3.org/2000/svg";

    using (var document = new SVGDocument())
    {
        var svgElement = document.RootElement;

        // Create a <rect> element and set the "fill" and "filter" attributes
        var rectElement = (SVGRectElement)document.CreateElementNS(SvgNamespace, "rect");
        rectElement.X.BaseVal.Value = 40;
        rectElement.Y.BaseVal.Value = 40;
        rectElement.Width.BaseVal.Value = 60;
        rectElement.Height.BaseVal.Value = 60;
        rectElement.SetAttribute("fill", "#ffa500");
        rectElement.SetAttribute("filter", "url(#F1)");
        svgElement.AppendChild(rectElement);

        // Create a <defs> element and add it to the <svg> element
        var defsElement = (SVGDefsElement)document.CreateElementNS(SvgNamespace, "defs");
        svgElement.AppendChild(defsElement);

        // Create a <filter> element and add it to the <defs> element
        var filterElement = (SVGFilterElement)document.CreateElementNS(SvgNamespace, "filter");
        filterElement.SetAttribute("x", "-20px");
        filterElement.SetAttribute("y", "-20px");
        filterElement.SetAttribute("height", "100px");
        filterElement.SetAttribute("width", "100px");
        filterElement.Id = "F1";
        defsElement.AppendChild(filterElement);

        // Create a <feGaussianBlur> element and add it to the <filter> element
        var feGaussianBlurElement = (SVGFEGaussianBlurElement)document.CreateElementNS(SvgNamespace, "feGaussianBlur");
        feGaussianBlurElement.In1.BaseVal = "SourceGraphic";
        feGaussianBlurElement.StdDeviationX.BaseVal = 10;
        feGaussianBlurElement.StdDeviationY.BaseVal = 10;
        filterElement.AppendChild(feGaussianBlurElement);

        // Save the document
        document.Save(Path.Combine(OutputDir, "gaussian-blur.svg"));
    }

If you render the result file, you will see a blurred orange rectangle exactly like the one in the previous figure, second in order with stdDeviation=“10”.

Blur Background Image

To use the Gaussian blur SVG filter for background blur, you can apply the filter to an SVG element that acts as a background behind the main content. It may be, for example, any bitmap. The blur filter allows you to create a visually appealing background blur effect while keeping the foreground content sharp and in focus.

To achieve background image blur with SVG, follow these few steps. They are similar to the steps described in the previous C# example:

1. Create an instance of the SVGDocument class.
2. The RootElement property of the SVGDocument class points to the document’s root <svg> element.
3. You can use the CreateElementNS(namespaceURI, QualifiedName) method of the SVGDocument class to create instances of the SVGImageElement, SVGDefsElement, SVGFilterElement, and SVGFEGaussianBlurElement classes.
   For example, as you plan to use a bitmap as a background, create an instance of the SvgImageElement class and set attributes specifying its source, position, and size. To add an imageElement to svgElement, you can use the AppendChild() method. Using a filter attribute of imageElement referring to the url name of filterElement (in id attribute) allows applying the SVG filter effect to the image.
4. Add all necessary attributes to the created elements and properly nest them.
5. After you make a blur filter and set a filterElement.Id for <filter> element, it can be applied to the image.
6. Call the Save() method to save the document with the blur background image to a local file specified by path.

Here is an example that illustrates blur background image implementation:

using Aspose.Svg;
using System.IO;
using Aspose.Svg.Filters;
...

    // Set SVG Namespace Url
    string SvgNamespace = "http://www.w3.org/2000/svg";

    using (var document = new SVGDocument())
    {
        var svgElement = document.RootElement;

        // Create an <image> element and add to the <svg> element
        var imageElement = (SVGImageElement)document.CreateElementNS(SvgNamespace, "image");
        imageElement.Href.BaseVal = "http://docs.aspose.com/svg/images/api/seaside.jpg";
        imageElement.Height.BaseVal.Value = 480;
        imageElement.Width.BaseVal.Value = 640;
        imageElement.X.BaseVal.Value = 20;
        imageElement.Y.BaseVal.Value = 20;
        imageElement.SetAttribute("filter", "url(#F1)");
        svgElement.AppendChild(imageElement);

        // Create a <defs> element and add to the <svg> element
        var defsElement = (SVGDefsElement)document.CreateElementNS(SvgNamespace, "defs");
        svgElement.AppendChild(defsElement);

        // Create a <filter> element and add to the <defs> element
        var filterElement = (SVGFilterElement)document.CreateElementNS(SvgNamespace, "filter");
        filterElement.Id = "F1";
        defsElement.AppendChild(filterElement);

        // Create a <feGaussianBlur> element and add to the <filter> element
        var feGaussianBlurElement = (SVGFEGaussianBlurElement)document.CreateElementNS(SvgNamespace, "feGaussianBlur");
        feGaussianBlurElement.In1.BaseVal = "SourceGraphic";
        feGaussianBlurElement.StdDeviationX.BaseVal = 5;
        feGaussianBlurElement.StdDeviationY.BaseVal = 5;
        filterElement.AppendChild(feGaussianBlurElement);

        // Save the document
        document.Save(Path.Combine(OutputDir, "blur-background-image.svg"));
    }

See also

• You can download the complete examples and data files from GitHub.
• About downloading from GitHub and running examples, you find out from the How to Run the Examples section.
• For more information about filter primitives, see the W3C Filter Effects Module page and the SVG Filters and Gradients article.
• Aspose.SVG offers free SVG Web Applications for converting SVG or image files, merging SVGs, image vectorizing, SVG sprite generating, SVG to Base64 data encoding, and more. These online applications work on any operating system with a web browser and don’t require additional software installation. It’s a fast and easy way to efficiently and effectively solve your SVG-related tasks!