Combine Images with Transparency - C# .NET 6

This tutorial shows how to merge an image with a transparent area on top of a background image in a C# .NET 6 Console application that uses LEADTOOLS image processing classes.

Required Knowledge

Get familiar with the basic steps of creating a project and loading and saving images, by reviewing the Add References and Set a License and Load and Save Images tutorials, before working on this tutorial.

Create the Project and Add LEADTOOLS References

Start with a copy of the project created in the Add References and Set a License tutorial. If the project is not available, follow the steps in that tutorial to create it.

The references needed depend upon the purpose of the project. References can be added by one or the other of the following two methods (but not both). For this project, the following references are needed:

If using NuGet references, this tutorial requires the following NuGet packages:

• Leadtools.Formats.Raster.Common
• Leadtools.Image.Processing

If local DLL references are used, the following DLLs are needed. The DLLs are located at <INSTALL_DIR>\LEADTOOLS23\Bin\net:

• Leadtools.dll
• Leadtools.Codecs.dll
• Leadtools.ImageProcessing.Effects.dll

For a complete list of which DLL files are required for your application, refer to Files to be Included With Your Application.

Set the License File

The License unlocks the features needed for the project. It must be set before any toolkit function is called. For details, including tutorials for different platforms, refer to Setting a Runtime License.

There are two types of runtime licenses:

• Evaluation license, obtained at the time the evaluation toolkit is downloaded. It allows the toolkit to be evaluated.
• Deployment license. If a Deployment license file and developer key are needed, refer to Obtaining a License.

Add the Code to Create and Load the Two Images to be Combined

With the project created, the references added, and the license set, coding can begin.

Open Program.cs in the Solution Explorer and add the following statements to the using block at the top.

using Leadtools; 
using Leadtools.Codecs; 
using Leadtools.ImageProcessing.Effects; 

Add the following code in the Main method after the call to InitLEAD that will load an image containing transparency as well as create a solid color background image that will be combined with it.

// Add code below to the Main() method after the call to SetLicense() 
// See Note below for where to obtain imagePlusAlpha.png 
string fileWithAlpha = @"FILE PATH TO imagePlusAlpha.png"; 
using RasterCodecs codecs = new(); 
 
CodecsImageInfo info = codecs.GetInformation(fileWithAlpha, false); 
if (info.HasAlpha) 
{ 
   RasterImage backgroundImage = RasterImage.Create(info.Width, info.Height, 24, info.XResolution, RasterColor.FromKnownColor(RasterKnownColor.CornflowerBlue)); 
   RasterImage imageWithAlpha = codecs.Load(fileWithAlpha, 32, CodecsLoadByteOrder.Bgr, 1, 1); 
   RasterImage combinedImage = CombineTransparentImage(imageWithAlpha, backgroundImage); 
   codecs.Save(combinedImage, @"C:\LEADTOOLS23\Resources\Images\combinedImage.jpg", RasterImageFormat.Jpeg411, 24); 
} 

Note

The image with transparency used for this tutorial, imagePlusAlpha.png, can be obtained from the output of the code in the tutorial, Add Transparency to an Image - Console C#, which adds transparency to a sample image.

Add the Code to Combine the Background and Transparent Images

Use the code below to add a new method called CombineTransparentImage that will combine the loaded transparent image with the solid color background image using the FeatherAlphaBlendCommand image processing class.

static RasterImage CombineTransparentImage(RasterImage imageWithAlpha, RasterImage backgroundImage) 
{ 
   RasterImage maskImage = imageWithAlpha.CreateAlphaImage(); 
   RasterImage outputImage = backgroundImage.Clone(); 
   LeadRect rect = new LeadRect(0, 0, outputImage.Width, outputImage.Height); 
   FeatherAlphaBlendCommand blend = new FeatherAlphaBlendCommand(imageWithAlpha, new LeadPoint(0, 0), rect, maskImage); 
   blend.Run(outputImage); 
   return outputImage; 
} 

Handling Streams

To use MemoryStream to load the file, replace the existing code in the Main method with the following:

static void Main(string[] args) 
{ 
   try 
   { 
      InitLEAD(); 
      string fileWithAlpha = @"C:\LEADTOOLS23\Resources\Images\imagePlusAlpha.png"; 
      using (RasterCodecs codecs = new RasterCodecs()) 
 
      // Load using Memory Stream 
      byte[] fileWithAlphaData = File.ReadAllBytes(fileWithAlpha); 
      using (MemoryStream fileWithAlphaStream = new MemoryStream(fileWithAlphaData)) 
 
      CodecsImageInfo info = codecs.GetInformation(fileWithAlphaStream, false); 
      if (info.HasAlpha) 
      { 
         RasterImage backgroundImage = RasterImage.Create(info.Width, info.Height, 24, info.XResolution, RasterColor.FromKnownColor(RasterKnownColor.CornflowerBlue)); 
         RasterImage imageWithAlpha = codecs.Load(fileWithAlphaStream); 
         RasterImage combinedImage = CombineTransparentImage(imageWithAlpha, backgroundImage); 
 
         // Save to Memory Stream 
         MemoryStream outputStream = new MemoryStream(); 
         codecs.Save(combinedImage, outputStream, RasterImageFormat.Jpeg411, 24); 
      } 
   } 
   catch (Exception ex) 
   { 
      Console.WriteLine(ex.ToString()); 
   } 
   Console.WriteLine("Press any key to exit..."); 
   Console.ReadKey(true); 
} 

Run the Project

Run the project by pressing F5, or by selecting Debug -> Start Debugging.

If the steps are followed correctly, the application loads an image containing a transparent alpha channel then combines it with a solid color background image. The result is then saved to a file on disk.

Wrap-up

This tutorial showed how to add the necessary references to combine a transparent image with a solid color background using the FeatherAlphaBlendCommand class.

See Also

• LEADTOOLS FeatherAlphaBlendCommand Documentation
• LEADTOOLS RasterCodecs Documentation
• LEADTOOLS SDK Download