Image Opacity in PdfSharp.NET - pdf

Question

I'm using PDFSharp.NET library to watermark a list of PDFs file. Everything works fine, the website has a lot of samples.
http://www.pdfsharp.net/wiki/Graphics-sample.ashx
The last thing I need is to add the Company Logo, which is big, in the middle of the PDF Page.
I can use a PNG, so that areas which are set as transparent do not "cover" the PDF page".
The pdf is not generated using PDFSharp, but is an "Image" PDF.
For this reason, what I need, is, in addition to the transparency, which works, be able some how to set the Image Opacity!
The code to place the image is this one:
XGraphics gfx = XGraphics.FromPdfPage(page, XGraphicsPdfPageOptions.Append);
XImage image = XImage.FromFile(mypath);
gfx.DrawImage(image, pwidth/2-image.PixelWidth/2, pheight/2 image.PixelHeight/2);
gfx.Dispose();
Anyone has already faced with that?

Answer 1

I don't know how to alter the opacity of an image while drawing it using PDFsharp (and I'm afraid this can't be done).
So instead I would just open the logo (PNG) with an image processor and set the opacity there.

Answer 2

I was looking in to this aswell now for making a watermark (companyLogo) to place over pdf sheets. The code below lets you change the opacity.
PDFSharp can not change the image opacity. What you can do is change the image you feed to PDF sharp. This has already been answered so I am just sharing my code of doing so.
private void DrawGraphics()
{
XGraphics gfx = XGraphics.FromPdfPage(page, XGraphicsPdfPageOptions.Append);
Image myTransparenImage = SetImageOpacity(Image.FromFile("MyPath"), (float)opacityYouwant); // opacityYouWant has to be a value between 0.0 and 1.0
XImage image = XImage.FromBitmapSource(Convert(myTransparenImage));
gfx.DrawImage(image, pwidth / 2 - image.PixelWidth / 2, pheight / 2 image.PixelHeight / 2);
gfx.Dispose();
}
public Image SetImageOpacity(Image image, float opacity)
{
try
{
//create a Bitmap the size of the image provided
Bitmap bmp = new Bitmap(image.Width, image.Height);
//create a graphics object from the image
using (Graphics gfx = Graphics.FromImage(bmp))
{
//create a color matrix object
ColorMatrix matrix = new ColorMatrix();
//set the opacity
matrix.Matrix33 = opacity;
//create image attributes
ImageAttributes attributes = new ImageAttributes();
//set the color(opacity) of the image
attributes.SetColorMatrix(matrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);
//now draw the image
gfx.DrawImage(image, new Rectangle(0, 0, bmp.Width, bmp.Height), 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, attributes);
}
return bmp;
}
catch (Exception ex)
{
MessageBox.Show(ex.Message);
return null;
}
}
public BitmapImage Convert(Image img)
{
using (var memory = new MemoryStream())
{
img.Save(memory, ImageFormat.Png);
memory.Position = 0;
var bitmapImage = new BitmapImage();
bitmapImage.BeginInit();
bitmapImage.StreamSource = memory;
bitmapImage.CacheOption = BitmapCacheOption.OnLoad;
bitmapImage.EndInit();
return bitmapImage;
}
}