How do I add an Image Mask?

[Ryan]

Question:

I am trying to add an image mask using the following code, but get an exception.

using (PDFDoc doc = new PDFDoc())
using (ElementBuilder bld = new ElementBuilder())
using (ElementWriter writer = new ElementWriter())
{
    Page page = doc.PageCreate();
    writer.Begin(page);
    Image img = Image.Create(doc, "Image.png");
    Image maskImage = Image.Create(doc, "MaskImage.tif");
    img.SetMask(maskImage); // throws the exception!!!
    System.Drawing.Bitmap bmp;
    Element element = bld.CreateImage(img, new Matrix2D(200, 0, 0, 250, 50, 500));
    writer.WritePlacedElement(element);
    writer.End();
    doc.PagePushBack(page);
    doc.Save("out.pdf", SDFDoc.SaveOptions.e_remove_unused);
}

The exception:

 

Unhandled Exception: pdftron.Common.PDFNetException: Exception:
         Message: Bad params
         Conditional expression: !IsImageMask() && image_mask.IsImageMask()
         Filename   : Image.cpp
         Function   : trn::PDF::Image::SetMask
         Linenumber : 864

Answer:

Image.Create creates a "regular" image, which needs two changes to be a Mask.

Image maskImage = Image.Create(doc, "MaskImage109.tif");
Obj obj = maskImage.GetSDFObj();
obj.PutBool("ImageMask", true);
obj.Erase("ColorSpace");

So final code would be

using (PDFDoc doc = new PDFDoc())
using (ElementBuilder bld = new ElementBuilder())
using (ElementWriter writer = new ElementWriter())
{
    Page page = doc.PageCreate();
    writer.Begin(page);
    Image img = Image.Create(doc, "Image.png");
    Image maskImage = Image.Create(doc, "MaskImage.tif");
    Obj obj = maskImage.GetSDFObj();
    obj.PutBool("ImageMask", true);
    obj.Erase("ColorSpace");
    img.SetMask(maskImage);
    System.Drawing.Bitmap bmp;
    Element element = bld.CreateImage(img, new Matrix2D(200, 0, 0, 250, 50, 500));
    writer.WritePlacedElement(element);
    writer.End();
    doc.PagePushBack(page);
    doc.Save("out.pdf", SDFDoc.SaveOptions.e_remove_unused);
}