Overprint is a way of combining colors when dealing with subtractive color spaces such as CMYK or DeviceN.

Normally, when one color is painted over another, it replaces the underlying color. So a black over a cyan becomes yellow. If Overprint is set, then the top color may be placed over the top of the base color. So black over cyan becomes a mixture of both black and cyan inks. This can be useful for printing purposes.

In ABCpdf, overprint is only applied when the Overprint property is set to true, the output ColorSpace is CMYK, the IccOutput is "device", the PDF graphics state indicates that overprint mode should be applied (see the Adobe PDF Specification for details) and no transparency has been detected.

The following example shows the effect that this parameter has on PDF rendering.

Set theDoc = Server.CreateObject("ABCpdf11.Doc")
' Open document with overprint
theDoc.Read "C:\WSG\Projects\ABCpdf\TestSuite\mypics\Overprint.pdf"
' Render the document (we need to go to CMYK for overprint)
theDoc.Rendering.ColorSpace = "CMYK"
theDoc.Rendering.Overprint = True
theDoc.Rendering.IccRgb = "device"
theDoc.Rendering.IccGray = "device"
theDoc.Rendering.IccCmyk = "device"
theDoc.Rendering.IccOutput = "device"
' Put image back into another PDF and render the document as RGB
' (so that we can see the effect of the overprint in RGB)
Set theRgb = Server.CreateObject("ABCpdf11.Doc")
theRgb.AddImageData theDoc.Rendering.GetData(".tif"), 1
theDoc.Clear
theRgb.Rendering.DotsPerInch = 36
theRgb.Rendering.ColorSpace = "RGB"
theRgb.Rendering.Save "C:\WSG\Projects\ABCpdf\TestSuite\TestEx\RenderingOverprint.png"
theRgb.Clear

RenderingOverprint.png