Unsharp Mask Effect

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.

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.

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