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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:
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:
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");
}
}
}
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:
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.
Spire.PDF for .NET is a PDF library that meets customers need with fast speed and high efficiency.
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