The Laplacian filter is used for detection of edges in an image. It highlights areas in which intensity changes rapidly producing a picture of all the edges in an image.

 

   

Settings
 
Name Default Description
Radius 0.8 pixels

This value determines the size of the edges that are detected.

This value represents the standard deviation of the Laplacian of Gaussian function.

 

   

Workings
 

The Laplacian filter is a standard Laplacian of Gaussian convolution. This is a second derivative function designed to measure changes in intensity without being overly sensitive to noise. The function produces a peak at the start of the change in intensity and then at the end of the change.

Because the Laplacian of Gaussian produces a fairly wide convolution for a small radius this filter can become quite computationally expensive as radius is increased.

 

   

Example
 

The following examples show the effect of a Laplacian filter applied with a number of different settings.

[C#]
void function() {
  using (Doc doc = new Doc()) {
    AddImagePage(doc, img3); // original image
    doc.Rendering.Save("EffectLaplacian.jpg");
    using (ImageLayer layer = AddImagePage(doc, img3)) {
      using (EffectOperation effect = new EffectOperation("Laplacian")) {
        effect.Parameters["Radius"].Value = 0.8;
        effect.Apply(layer.PixMap);
      }
    }
    doc.Rendering.Save("EffectLaplacian08.jpg");
    using (ImageLayer layer = AddImagePage(doc, img3)) {
      using (EffectOperation effect = new EffectOperation("Laplacian")) {
        effect.Parameters["Radius"].Value = 1.6;
        effect.Apply(layer.PixMap);
      }
    }
    doc.Rendering.Save("EffectLaplacian16.jpg");
    using (ImageLayer layer = AddImagePage(doc, img3)) {
      using (EffectOperation effect = new EffectOperation("Laplacian")) {
        effect.Parameters["Radius"].Value = 3.2;
        effect.Apply(layer.PixMap);
      }
    }
    doc.Rendering.Save("EffectLaplacian32.jpg");
  }
}

[Visual Basic]
Sub ...
  Using doc As New Doc()
    AddImagePage(doc, img3)
    ' original image
    doc.Rendering.Save("EffectLaplacian.jpg")
    Using layer As ImageLayer = AddImagePage(doc, img3)
      Using effect As New EffectOperation("Laplacian")
        effect.Parameters("Radius").Value = 0.8
        effect.Apply(layer.PixMap)
      End Using
    End Using
    doc.Rendering.Save("EffectLaplacian08.jpg")
    Using layer As ImageLayer = AddImagePage(doc, img3)
      Using effect As New EffectOperation("Laplacian")
        effect.Parameters("Radius").Value = 1.6
        effect.Apply(layer.PixMap)
      End Using
    End Using
    doc.Rendering.Save("EffectLaplacian16.jpg")
    Using layer As ImageLayer = AddImagePage(doc, img3)
      Using effect As New EffectOperation("Laplacian")
        effect.Parameters("Radius").Value = 3.2
        effect.Apply(layer.PixMap)
      End Using
    End Using
    doc.Rendering.Save("EffectLaplacian32.jpg")
  End Using
End Sub

   
   


Original Image before Laplacian Filter

 

 


Laplacian Radius 0.8 Pixels

 

 


Laplacian Radius 1.6 Pixels

 

 


Laplacian Radius 3.2 Pixels