| DefaultHalftone Property | ||||||||||
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Notes
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Specifies the default halftone type and options. The default halftone remains in effect until an embedded
halftone screen is encountered. The Type can be:
If the type is Spot then an angle in degrees, frequency and spot function can also be specified. These should be separated by commas with no extraneous spaces. The spot functions available are:
If the type is Threshold you should specify a value - for example "'threshold=60". This is used when calculating the value of a black and white pixel. If the grey level l is greater than the threshold the pixel will be black otherwise it will be white. For full details of how Halftones work you should see the Adobe
PDF Specification available from the Adobe web site.
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Example
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The following example shows the effect that this parameter has on PDF rendering.
using var doc = new Doc();
using var image = new XImage();
image.SetFile(Server.MapPath("../mypics/Shuttle.jpg"));
doc.Rect.String = image.Selection.String;
doc.AddImage(image);
// Save rendered image as black and white picture using Line spot function
doc.Rendering.UseEmbeddedHalftone = false;
doc.Rendering.DotsPerInch = 50;
doc.Rendering.ColorSpace = XRendering.ColorSpaceType.Gray;
doc.Rendering.BitsPerChannel = 1;
doc.Rendering.DefaultHalftone = "Spot,30,100,Line";
doc.Rendering.Save(Server.MapPath("RenderingHalftoneLine.png"));
// Save rendered image as black and white picture using Diamond spot function
doc.Rendering.DefaultHalftone = "Spot,0,100,Diamond";
doc.Rendering.Save(Server.MapPath("RenderingHalftoneDiamond.png"));
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