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C# Wrapper to the FreeImage DLL for graphical image format conversion

, 30 Sep 2003
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This article provides a simplified C# wrapper to the FreeImage project for graphical file format conversion.


FreeImage is an extremely useful Open Source project for reading, manipulating and converting a large amount of graphical formats. However at present the library exists as Win32 Dynamic Link Library. As my latest fascination is C#, I decided to create a simple Interop wrapper for it.

Using the code

The code is very straightforward to use, which is a reflection on the FreeImage implementation itself. For my needs I wanted to be able to take a picture file in Portable Bitmap (PBM) format and convert it to a standard Bitmap (BMP). For this I needed 3 methods exposed via the FreeImage DLL, FreeImage_Load, FreeImage_Save and FreeImage_Unload, the signature for which are:

       const char *filename, int flags FI_DEFAULT(0));
   FIBITMAP *dib, const char *filename, int flags FI_DEFAULT(0)); 
DLL_API void DLL_CALLCONV FreeImage_Unload(FIBITMAP* dib);

Now the C# Interop signatures for these are:

public class FreeImage
     public static extern int FreeImage_Load(FIF format,
                    string filename, int flags);

     public static extern void FreeImage_Unload(int handle);

     public static extern bool FreeImage_Save(FIF format,
        int handle, string filename, int flags);

As an example, to convert a graphical image from PBM to BMP, all you need to do is the following (note the enum FIF is not documented here, but can be found in the source code).

namespace Test
    class MainClass
        public static void Main(string[] args)
            int handle = FreeImageAPI.FreeImage.FreeImage_Load(


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

David Boland
Web Developer
United States United States
No Biography provided

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Comments and Discussions

GeneralRe: Unable to find an entry point (FreeImage_CloseMultiBitmap) Pin
DeeJayX13-Mar-06 1:53
memberDeeJayX13-Mar-06 1:53 
GeneralRe: Unable to find an entry point (FreeImage_CloseMultiBitmap) Pin
DeeJayX13-Mar-06 1:53
memberDeeJayX13-Mar-06 1:53 
AnswerRe: Unable to find an entry point (FreeImage_CloseMultiBitmap) Pin
vor0nwe26-Apr-06 6:30
membervor0nwe26-Apr-06 6:30 
GeneralDDS and Freeimage Pin
cococvg27-Apr-05 1:23
membercococvg27-Apr-05 1:23 
GeneralUnable to load DLL (FreeImage.dll). Pin
TechTiger24-Mar-04 15:00
memberTechTiger24-Mar-04 15:00 
GeneralRe: Unable to load DLL (FreeImage.dll). Pin
David Boland25-Mar-04 0:55
memberDavid Boland25-Mar-04 0:55 
GeneralDisplaying in .NET Pin
furkinfedup26-Oct-03 2:37
memberfurkinfedup26-Oct-03 2:37 
GeneralRe: Displaying in .NET Pin
schoeneck10-Nov-03 12:22
memberschoeneck10-Nov-03 12:22 
That's what I thought, too. But I haven't tried yet. Perhaps it is really better to convert the image first and then load. although this may take longer than directly displaying it.

Perhaps David Boland can implement an enhancement to System.Drawing.Image class in the future.

I would be one of the first using it, and helping, of course!

GeneralRe: Displaying in .NET Pin
David Boland10-Nov-03 23:58
memberDavid Boland10-Nov-03 23:58 
GeneralRe: Displaying in .NET Pin
Drolon17-Nov-03 8:15
memberDrolon17-Nov-03 8:15 
GeneralRe: Displaying in .NET Pin
furkinfedup24-Jan-04 0:26
memberfurkinfedup24-Jan-04 0:26 
GeneralRe: Displaying in .NET Pin
persée23-Aug-05 5:41
memberpersée23-Aug-05 5:41 
GeneralMemory or File... Pin
Drew Stainton1-Oct-03 8:46
memberDrew Stainton1-Oct-03 8:46 
GeneralRe: Memory or File... Pin
Anonymous1-Oct-03 23:38
sussAnonymous1-Oct-03 23:38 
QuestionHow to draw FIBITMAP to form. Pin
Skyer1-Oct-03 5:30
memberSkyer1-Oct-03 5:30 
AnswerRe: How to draw FIBITMAP to form. Pin
David Boland1-Oct-03 6:09
memberDavid Boland1-Oct-03 6:09 
GeneralAccessing the image Pin
Ray Hayes1-Oct-03 2:36
memberRay Hayes1-Oct-03 2:36 
GeneralRe: Accessing the image Pin
David Boland1-Oct-03 6:20
memberDavid Boland1-Oct-03 6:20 
GeneralSystem::Drawing::Image Pin
Jonathan de Halleux1-Oct-03 2:36
memberJonathan de Halleux1-Oct-03 2:36 
GeneralRe: System::Drawing::Image Pin
David Boland1-Oct-03 6:15
memberDavid Boland1-Oct-03 6:15 

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