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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.

Introduction

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:

DLL_API FIBITMAP *DLL_CALLCONV FreeImage_Load(FREE_IMAGE_FORMAT fif, 
       const char *filename, int flags FI_DEFAULT(0));
 
DLL_API BOOL DLL_CALLCONV FreeImage_Save(FREE_IMAGE_FORMAT fif, 
   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
    {
         [DllImport("FreeImage.dll")]
         public static extern int FreeImage_Load(FIF format, 
                        string filename, int flags);
         
         [DllImport("FreeImage.dll")]
         public static extern void FreeImage_Unload(int handle);
         
         [DllImport("FreeImage.dll")]
         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(
                FreeImageAPI.FIF.FIF_PBM,
                @"c:\image.pbm", 
                0);
                          
            FreeImageAPI.FreeImage.FreeImage_Save(
                FreeImageAPI.FIF.FIF_BMP,   
                handle, 
                @"c:\image.bmp", 
                0);
 
            FreeImageAPI.FreeImage.FreeImage_Unload(handle);          
        }
    }
}

License

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

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About the Author

David Boland
Web Developer
United States United States
No Biography provided

Comments and Discussions

 
GeneralRe: Unable to find an entry point (FreeImage_CloseMultiBitmap) PinmemberDeeJayX13-Mar-06 1:53 
AnswerRe: Unable to find an entry point (FreeImage_CloseMultiBitmap) Pinmembervor0nwe26-Apr-06 6:30 
GeneralDDS and Freeimage Pinmembercococvg27-Apr-05 1:23 
GeneralUnable to load DLL (FreeImage.dll). PinmemberTechTiger24-Mar-04 15:00 
I'm using C# to try to implement this, but I've got an error message saying "Uable to load DLL (FreeImage.dll).
 
When I was trying to add an reference to the dll. It said "A reference to .... could not be added. This is not a valid assembly or COM component."
 
Any idea?
GeneralRe: Unable to load DLL (FreeImage.dll). PinmemberDavid Boland25-Mar-04 0:55 
GeneralDisplaying in .NET Pinmemberfurkinfedup26-Oct-03 2:37 
GeneralRe: Displaying in .NET Pinmemberschoeneck10-Nov-03 12:22 
GeneralRe: Displaying in .NET PinmemberDavid Boland10-Nov-03 23:58 
GeneralRe: Displaying in .NET PinmemberDrolon17-Nov-03 8:15 
GeneralRe: Displaying in .NET Pinmemberfurkinfedup24-Jan-04 0:26 

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