Set Transparency for PDF Image in C#, VB.NET

This section aims at providing developers a detail solution to set transparency for image in PDF file with C#, VB.NET via this PDF api Spire.PDF for .NET.

Spire.PDF for .NET enables you to set transparency for PDF image directly by utilizing one core method: Spire.Pdf.PdfPageBase.Canvas.SetTransparency(float alphaPen, float alphaBrush, PdfBlendMode blendMode); There are three parameters passed in this method. The first parameter is the alpha value for pen operations; while the second parameter is the alpha value for brush operations; and the last parameter is the blend mode. Now, let us see how to set PDF transparency step by step.

Set Transparency Images in PDF File

Step1: Prepare an image file

In my solution, I need create a new PDF file and insert an existing image file to PDF. Finally set transparency for this PDF image. So I prepare an image as below:

Draw Transparency Images

Step2: Download and Install Spire.PDF for .NET

Spire.PDF for .NET is a PDF component that enables developers to generate, read, edit and handle PDF files without Adobe Acrobat. Here you can download Spire.PDF for .NET and install it on system.

Step3: Start a new project and Add references

We can create a project either in Console Application or in Windows Forms Application, either in C# or in VB.NET. Here I use C# Console Application. Since we will use Spire.PDF for .NET, we need add Spire.Pdf.dll as reference. The default path is “..\Spire.PDF\Bin\NET4.0\ Spire.Pdf.dll”

Step 4: Set PDF transparency for PDF image

In this step, first, I initialize a new instance of the class Spire.Pdf.PdfDocument and add a section in the newly created PDF. Then, load the image I have already prepared to the PDF and set the PDF image size. Finally set transparency for this PDF image. When I set transparency, I add a title for the transparency and set position and format for it. After I save the image in PDF by calling this method: PdfPageBase.Canvas.DrawImage(PdfImage image, float x, float y, float width, float height).Then, by using this method: PdfPageBase.Canvas.SetTransparency(float alphaPen, float alphaBrush, PdfBlendMode blendMode); I successfully set transparency for this PDF image. Here we can see the whole code:

[C#]
using Spire.Pdf;
using Spire.Pdf.Graphics;
using System;
using System.Drawing;

namespace SetTransparencyOfImage
{
    class Program
    {
        static void Main(string[] args)
        {
            //Initiate a new instance of PdfDocument 
            PdfDocument doc = new PdfDocument();
            //Add one section to the PDF document
            PdfSection section = doc.Sections.Add();
            //Open Image File
            PdfImage image = PdfImage.FromFile(@"..\016.png");
            //Set the Image size in PDF file
            float imageWidth = image.PhysicalDimension.Width / 2;
            float imageHeight = image.PhysicalDimension.Height / 2;

            //Set PDF granphic transparency 
            foreach (PdfBlendMode mode in Enum.GetValues(typeof(PdfBlendMode)))
            {
                PdfPageBase page = section.Pages.Add();
                float pageWidth = page.Canvas.ClientSize.Width;
                float y = 1;
                //Set transparency image title, title position and format
                y = y + 5;
                PdfBrush brush = new PdfSolidBrush(Color.Firebrick);
                PdfTrueTypeFont font = new PdfTrueTypeFont(new Font("Arial", 16f, FontStyle.Bold));
                PdfStringFormat format = new PdfStringFormat(PdfTextAlignment.Center);
                String text = String.Format("Transparency Blend Mode: {0}", mode);
                page.Canvas.DrawString(text, font, brush, pageWidth / 2, y, format);
                SizeF size = font.MeasureString(text, format);
                y = y + size.Height + 6;
                //write and save the image loaded into PDF
                page.Canvas.DrawImage(image, 0, y, imageWidth, imageHeight);
                page.Canvas.Save();
                //set left and top distance between graphic images
                float d = (page.Canvas.ClientSize.Width - imageWidth) / 5;
                float x = d;
                y = y + d / 2;
                for (int i = 0; i < 5; i++)
                {
                    float alpha = 1.0f / 6 * (5 - i);
                    //set transparency to be alpha
                    page.Canvas.SetTransparency(alpha, alpha, mode);
                    //draw transparency images for the original PDF image
                    page.Canvas.DrawImage(image, x, y, imageWidth, imageHeight);
                    x = x + d;
                    y = y + d / 2;
                }
                page.Canvas.Restore();
            }
            //Save pdf file.
            doc.SaveToFile("Transparency.pdf");
            doc.Close();
            //Launching the Pdf file.
            System.Diagnostics.Process.Start("Transparency.pdf");
        }
    }
}
[VB.NET]
Imports Spire.Pdf
Imports Spire.Pdf.Graphics
Imports System.Drawing

Namespace SetTransparencyOfImage
	Class Program
		Private Shared Sub Main(args As String())
			'Initiate a new instance of PdfDocument 
			Dim doc As New PdfDocument()
			'Add one section to the PDF document
			Dim section As PdfSection = doc.Sections.Add()
			'Open Image File
			Dim image As PdfImage = PdfImage.FromFile("..\016.png")
			'Set the Image size in PDF file
			Dim imageWidth As Single = image.PhysicalDimension.Width / 2
			Dim imageHeight As Single = image.PhysicalDimension.Height / 2

			'Set PDF granphic transparency 
			For Each mode As PdfBlendMode In [Enum].GetValues(GetType(PdfBlendMode))
				Dim page As PdfPageBase = section.Pages.Add()
				Dim pageWidth As Single = page.Canvas.ClientSize.Width
				Dim y As Single = 1
				'Set transparency image title, title position and format
				y = y + 5
				Dim brush As PdfBrush = New PdfSolidBrush(Color.Firebrick)
				Dim font As New PdfTrueTypeFont(New Font("Arial", 16F, FontStyle.Bold))
				Dim format As New PdfStringFormat(PdfTextAlignment.Center)
				Dim text As [String] = [String].Format("Transparency Blend Mode: {0}", mode)
				page.Canvas.DrawString(text, font, brush, pageWidth / 2, y, format)
				Dim size As SizeF = font.MeasureString(text, format)
				y = y + size.Height + 6
				'write and save the image loaded into PDF
				page.Canvas.DrawImage(image, 0, y, imageWidth, imageHeight)
				page.Canvas.Save()
				'set left and top distance between graphic images
				Dim d As Single = (page.Canvas.ClientSize.Width - imageWidth) / 5
				Dim x As Single = d
				y = y + d / 2
				For i As Integer = 0 To 4
					Dim alpha As Single = 1F / 6 * (5 - i)
					'set transparency to be alpha
					page.Canvas.SetTransparency(alpha, alpha, mode)
					'draw transparency images for the original PDF image
					page.Canvas.DrawImage(image, x, y, imageWidth, imageHeight)
					x = x + d
					y = y + d / 2
				Next
				page.Canvas.Restore()
			Next
			'Save pdf file.
			doc.SaveToFile("Transparency.pdf")
			doc.Close()
			'Launching the Pdf file.
			System.Diagnostics.Process.Start("Transparency.pdf")
		End Sub
	End Class
End Namespace

Result Task

After performing above code, we can see the result PDF document as below:

Draw Transparency Images

I have set transparency for PDF image by Spire.PDF for .NET. I sincerely wish it can help you. We e-iceblue team appreciate any kind of queries, comments and advice at E-iceblue Forum. Our professionals are ready to reply you as quick as possible.

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