The Unsharp Mask filter is a simple method of sharpening a photo. Areas of complexity and fine detail within the image become crisp and better defined. An Unsharp Mask takes longer to perform than a simple Sharpen but gives more control and produces a more natural appearance.

 

   

Settings
 
Name Default Description
Radius 1.5 pixels

Determines the scale of fine detail that will be enhanced. Low values enhance only very fine detail while high values enhance larger levels of detail.

Amount 60 % The level of enhancement to be applied to the fine detail. Values greater than 100% will super-enhance any complex areas.
Threshold 0 If there is little fine detail then you can choose not to enhance it by setting a threshold. Any detail less than the threshold will not be enhanced.

 

   

Workings
 

An Unsharp Mask is essentially a Blur in reverse. A Gaussian Blur is applied to a copy of the original image to produce an image with no fine detail. The blurred image is subtracted from the original to extract the fine detail. This fine detail is then added to the original image to highlight complex areas.

The radius parameter determines the radius of the Gaussian Blur in pixels and lets you choose the level of scale of detail that should be enhanced. The difference between color levels on the blurred and original image is determined at each point on the image. If the difference is greater than the Threshold parameter then the Amount percentage of the difference is added back to the original image.

 

   

Example
 

The following example shows the basic effect of Unsharp Mask on a blurred photo and how the parameters can change the effect produced. Note that because JPEG compression has been used to compress these images some of the fine detail applied by the effect is not visible.

[C#]
void function() {
  using (Doc doc = new Doc()) {
    AddImagePage(doc, img5); // original image
    doc.Rendering.Save("EffectUnsharpMask1a.jpg");
    using (ImageLayer layer = AddImagePage(doc, img5)) {
      using (EffectOperation effect = new EffectOperation("Unsharp Mask")) {
        effect.Apply(layer.PixMap);
      }
    }
    doc.Rendering.Save("EffectUnsharpMask1b.jpg");
    AddImagePage(doc, img3); // original image
    doc.Rendering.Save("EffectUnsharpMask2a.jpg");
    using (ImageLayer layer = AddImagePage(doc, img3)) {
      using (EffectOperation effect = new EffectOperation("Unsharp Mask")) {
        effect.Apply(layer.PixMap);
      }
    }
    doc.Rendering.Save("EffectUnsharpMask2b.jpg");
    AddImagePage(doc, img6); // original image
    doc.Rendering.Save("EffectUnsharpMask3a.jpg");
    using (ImageLayer layer = AddImagePage(doc, img6)) {
      using (EffectOperation effect = new EffectOperation("Unsharp Mask")) {
        effect.Apply(layer.PixMap);
      }
    }
    doc.Rendering.Save("EffectSharpen3b.jpg");
    using (ImageLayer layer = AddImagePage(doc, img3)) {
      using (EffectOperation effect = new EffectOperation("Unsharp Mask")) {
        effect.Parameters["Amount"].Value = 140;
        effect.Apply(layer.PixMap);
      }
    }
    doc.Rendering.Save("EffectUnsharpMaskSetting1.jpg");
    using (ImageLayer layer = AddImagePage(doc, img3)) {
      using (EffectOperation effect = new EffectOperation("Unsharp Mask")) {
        effect.Parameters["Amount"].Value = 140;
        effect.Parameters["Radius"].Value = 6;
        effect.Apply(layer.PixMap);
      }
    }
    doc.Rendering.Save("EffectUnsharpMaskSetting2.jpg");
    using (ImageLayer layer = AddImagePage(doc, img3)) {
      using (EffectOperation effect = new EffectOperation("Unsharp Mask")) {
        effect.Parameters["Amount"].Value = 140;
        effect.Parameters["Radius"].Value = 6;
        effect.Parameters["Threshold"].Value = 40;
        effect.Apply(layer.PixMap);
      }
    }
    doc.Rendering.Save("EffectUnsharpMaskSetting3.jpg");
  }
}

[Visual Basic]
Sub ...
  Using doc As New Doc()
    AddImagePage(doc, img5)
    ' original image
    doc.Rendering.Save("EffectUnsharpMask1a.jpg")
    Using layer As ImageLayer = AddImagePage(doc, img5)
      Using effect As New EffectOperation("Unsharp Mask")
        effect.Apply(layer.PixMap)
      End Using
    End Using
    doc.Rendering.Save("EffectUnsharpMask1b.jpg")
    AddImagePage(doc, img3)
    ' original image
    doc.Rendering.Save("EffectUnsharpMask2a.jpg")
    Using layer As ImageLayer = AddImagePage(doc, img3)
      Using effect As New EffectOperation("Unsharp Mask")
        effect.Apply(layer.PixMap)
      End Using
    End Using
    doc.Rendering.Save("EffectUnsharpMask2b.jpg")
    AddImagePage(doc, img6)
    ' original image
    doc.Rendering.Save("EffectUnsharpMask3a.jpg")
    Using layer As ImageLayer = AddImagePage(doc, img6)
      Using effect As New EffectOperation("Unsharp Mask")
        effect.Apply(layer.PixMap)
      End Using
    End Using
    doc.Rendering.Save("EffectSharpen3b.jpg")
    Using layer As ImageLayer = AddImagePage(doc, img3)
      Using effect As New EffectOperation("Unsharp Mask")
        effect.Parameters("Amount").Value = 140
        effect.Apply(layer.PixMap)
      End Using
    End Using
    doc.Rendering.Save("EffectUnsharpMaskSetting1.jpg")
    Using layer As ImageLayer = AddImagePage(doc, img3)
      Using effect As New EffectOperation("Unsharp Mask")
        effect.Parameters("Amount").Value = 140
        effect.Parameters("Radius").Value = 6
        effect.Apply(layer.PixMap)
      End Using
    End Using
    doc.Rendering.Save("EffectUnsharpMaskSetting2.jpg")
    Using layer As ImageLayer = AddImagePage(doc, img3)
      Using effect As New EffectOperation("Unsharp Mask")
        effect.Parameters("Amount").Value = 140
        effect.Parameters("Radius").Value = 6
        effect.Parameters("Threshold").Value = 40
        effect.Apply(layer.PixMap)
      End Using
    End Using
    doc.Rendering.Save("EffectUnsharpMaskSetting3.jpg")
  End Using
End Sub


   


Original Image

 

 


Unsharp Mask Default Settings

 

 


Original Image

 

 


Unsharp Mask Default Settings

 

 


Original Image

 

 


Unsharp Mask Default Settings

 

 

 

The following examples show how the parameters can change the effect produced.

 

 


Unsharp Mask Default Settings

 

 


Unsharp Mask Amount =140

 

 


Unsharp Mask Amount =140 Radius = 6

 

 


Unsharp Mask Amount =140 Radius = 6 Threshold = 40