Add and apply a GaussianBlur effect on a image

winComposition-BlurEffect.cs

// Install win2D (nuget package)

// ParallaxImage is an Image Control in my Page.xaml
// ParallaxCanvas is a Canvas Control on my Page.xaml
// ParallaxCanvas contains ParallaxImage, so ParallaxCanvas is the parent of ParallaxImage

Visual _backgroundVisual = ElementCompositionPreview.GetElementVisual(ParallaxImage);
Compositor _backgroundCompositor = _backgroundVisual.Compositor;

GaussianBlurEffect blurEffect = new GaussianBlurEffect() {
    Name = "Blur",
    BlurAmount = 90.0f, // You can place your blur amount here.
    BorderMode = EffectBorderMode.Hard,
    Optimization = EffectOptimization.Balanced,
    Source = new CompositionEffectSourceParameter("Backdrop")
};

var effectFactory = _backgroundCompositor.CreateEffectFactory(blurEffect, new[] { "Blur.BlurAmount" });
var effectBrush = effectFactory.CreateBrush();

var destinationBrush = _backgroundCompositor.CreateBackdropBrush();
effectBrush.SetSourceParameter("Backdrop", destinationBrush);

var blurSprite = _backgroundCompositor.CreateSpriteVisual();
blurSprite.Size = new Vector2((float)ParallaxCanvas.ActualWidth, (float)ParallaxCanvas.ActualHeight);
blurSprite.Brush = effectBrush;
ElementCompositionPreview.SetElementChildVisual(ParallaxCanvas, blurSprite);