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Hi,

I am trying to change the color of an existing metafile(.emf) file from my machine and save it as another modified copy. I am able to render the run time metafile on the windows form but haven't been able to save it on my machine.

I have attached my code below and would be grateful if somebody can help.

What I have tried:

[DllImport("gdi32.dll")]
        static extern IntPtr CopyEnhMetaFile(  // Copy EMF to file
         IntPtr hemfSrc,   // Handle to EMF
         String lpszFile // File
       );

        [DllImport("gdi32.dll")]
        static extern int DeleteEnhMetaFile(  // Delete EMF
          IntPtr hemf // Handle to EMF
        );
        [DllImport("gdi32.dll")]
        static extern uint GetEnhMetaFileBits(IntPtr hemf, uint cbBuffer,
        [Out] byte[] lpbBuffer);

        private void PicModified_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            float[][] matrixColTrans =
                {
                        new float[] {0, 0, 0, 0, 0}
                        , new float[] {0, 0, 0, 0, 0}
                        , new float[] {0, 0, 0, 0, 0}
                        , new float[] {0, 204, 0, 1, 0}
                        , new float[] {0, 0, 0, 0, 0}
                    };
            ColorMatrix colorMatrix = new ColorMatrix(matrixColTrans);

            ImageAttributes ia = new ImageAttributes();
            ia.SetColorMatrix(colorMatrix);

            if (txtSelectEMFFilePath.Text.EndsWith(".emf"))
            {
                string destFileName = txtSelectEMFFilePath.Text;
                Metafile mf = new Metafile(destFileName);
                
                g.DrawImage(
                    mf
                    , new Rectangle(0, 0, picModified.Width, picModified.Height)// destination rectangle 
                    , 0, 0 // upper-left corner of source rectangle 
                    , mf.PhysicalDimension.Width // width of source rectangle
                    , mf.PhysicalDimension.Height // height of source rectangle
                    , GraphicsUnit.Pixel
                    , ia
                );
              
                // Save it as a metafile
                IntPtr iptrMetafileHandle = mf.GetHenhmetafile();

                // Export metafile to an image file
                IntPtr iptrMetafileHandleCopy = CopyEnhMetaFile(iptrMetafileHandle, "image.emf");
               
                //Binding Output file
                Image newimg = new Metafile("image.emf");
                imgOut.Image = newimg;
                imgOut.SizeMode = PictureBoxSizeMode.Zoom;

                //// Delete the metafile from memory
                DeleteEnhMetaFile(iptrMetafileHandle);
                DeleteEnhMetaFile(iptrMetafileHandleCopy);

                mf.Dispose();
                //1. End 
            }
        }
Posted
Updated 17-Jul-19 9:16am

1 solution

You need to get a separate encoder for this; as GDI+ cannot save those types of metafiles
Microsoft Docs:
Remarks
If no encoder exists for the file format of the image, the Portable Network Graphics (PNG) encoder is used. When you use the Save method to save a graphic image as a Windows Metafile Format (WMF) or Enhanced Metafile Format (EMF) file, the resulting file is saved as a Portable Network Graphics (PNG) file.
This behavior occurs because the GDI+ component of the .NET Framework does not have an encoder that you can use to save files as .wmf or .emf files.

Image.Save Method (System.Drawing) | Microsoft Docs[^]
 
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Comments
itm.abhishek 19-Jul-19 8:27am    
Hi, I tried Image.Save method but it only produces an image with .emf extension. It does not actually produce a true .emf file. I went through some articles on MSDN and found that CopyEnhMetaFile(iptrMetafileHandle, "image.emf") function actually copies the contents of an .emf file into a new one. But in my case, it's only copying the original file content into a new file and saving it back to the machine. The new file created by CopyEnhMetaFile function doesn't include the color changes done by g.DrawImage function in the above code.

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