Conversion of Enhanced Metafile to Bitmap and viceversa

• Download source files - 6 KB
• Download demo project - 24 KB
• Download sample EMF- 45 KB

Introduction

I have come across loads of libraries which convert images from one format to other, but most of them are confined to conversion between raster formats like BMP, JPG, GIF etc., This article explains a class which encapsulates the functionality of converting a vector file format (EMF) to raster file format (BMP). Once an EMF is converted to BMP raster file format, it can then be converted to any other format using the freely available libraries like CxImage.

Background

I had this problem of converting an EMF to BMP when I was doing my earlier project. I have searched a lot for help but couldn't find any except that many people asking similar question in discussion groups. I thought I should share this solution with others and wrote my first article to Code project. I hope it will be useful to you.

Using the code

Using this code is very simple. Just instantiate the class and call the convert function like this:

    CConvertEMFToBMP conv;
    
    //call the convert function

    BOOL bRet = conv.ConvertEMFToBMP(m_strEMF,m_strBMP,m_chkScale);

ConvertEMFToBMP takes three parameters:

//    m_strEMF - path and file name of EMF file to be converted

//    m_strBMP - path and file name of BMP file 

//    m_chkScale - boolean. If this is false, EMF is converted to 

//            BMP in original size.

//            If this is true, the image is scaled to preset size 

//            in the code (explained below)

Example:

    CConvertEMFToBMP conv;
    
    //call the convert function

    BOOL bRet = conv.ConvertEMFToBMP("D:\temp\Sample.emf",
            "D:\temp\sample.bmp",false);

To Convert a BMP to EMF:

    CConvertEMFToBMP conv;
       //call the convert function

    BOOL bRet = conv.ConvertBMPToEMF(m_strBMP,m_strEMF);

ConvertBMPToEMF takes two paramters:

    m_strBMP - path and file name of BMP file to be converted
    m_strEMF - path and file name of EMF file 

Example:

    CConvertEMFToBMP conv;
    
    //call the convert function

    BOOL bRet = conv.ConvertBMPToEMF("D:\temp\Sample.bmp",
             "D:\temp\sample.emf",false);

How Does it Work?

There is no straight forward technique to convert an EMF to BMP. ConvertEMFToBMP converts an EMF to Bitmap by playing the metafile in the MemoryDC and then getting the DIB bits and storing them in the bitmap format. To get the memory DC, an invisible window is created and destroyed at the end of conversion. alternatively, the source code can be modified to take the hwnd to the ConvertEMFToBMP function. The scale image option scales the image to a fixed size #defined in the source code. This can also be modified so as to scale as per the user passed parameter. I have used only API functions so as to make the code light avoiding the MFC DLLs. The following is the step by step explanation of core logic of conversion.

1. Create a window which is invisible, of any size

       //Create an invisible window
   
       HWND hWnd = CreateWindow("#32770","NULL",~WS_VISIBLE,0,0,
               100,100,NULL,NULL,NULL,0);
   

2. Get the DC of the window

       //Get the DC of the Window
   
       HDC dc = ::GetDC(hWnd);
   

3. Get the handle to the emf file and get the EMF header

       //Get the Handle from the enhanced metafile
   
       hemf = ::GetEnhMetaFile(strFileName);
           
       // Get the header from the enhanced metafile.
   
       ZeroMemory( &emh, sizeof(ENHMETAHEADER) );
       emh.nSize = sizeof(ENHMETAHEADER);
       if( GetEnhMetaFileHeader( hemf, 
                sizeof( ENHMETAHEADER ), &emh ) == 0 )
       {
           DeleteEnhMetaFile( hemf );
           return FALSE;
       }
       
   

4. Get the width and height of the EMF

       //Declare variables for calculation of metafile rect
   
       RECT    rect;
       float    PixelsX, PixelsY, MMX, MMY;
       
       float fAspectRatio;
       long lWidth,lHeight;
       
       // Get the characteristics of the output device.
   
       PixelsX = (float)GetDeviceCaps( dc, HORZRES );
       PixelsY = (float)GetDeviceCaps( dc, VERTRES );
       MMX = (float)GetDeviceCaps( dc, HORZSIZE );
       MMY = (float)GetDeviceCaps( dc, VERTSIZE );
       
       // Calculate the rect in which to draw the metafile based on the
   
       // intended size and the current output device resolution.
   
       // Remember that the intended size is given in 0.01 mm units, so
   
       // convert those to device units on the target device.
   
       rect.top = (int)((float)(emh.rclFrame.top) * 
               PixelsY / (MMY*100.0f));
       rect.left = (int)((float)(emh.rclFrame.left) * 
               PixelsX / (MMX*100.0f));
       rect.right = (int)((float)(emh.rclFrame.right) * 
               PixelsX / (MMX*100.0f));
       rect.bottom = (int)((float)(emh.rclFrame.bottom) * 
               PixelsY / (MMY*100.0f));
   
       //Calculate the Width and Height of the metafile
   
       lWidth = (long)((float)(abs(rect.left - rect.right)));
       lHeight =(long)((float)(abs(rect.top-rect.bottom )));
   

5. If the image needs to be scaled, modify the width and height as per the aspect ratio

       fAspectRatio = (float)lWidth/(float)lHeight;
   
       
       if(bScaleImage) //If miniature option is ON, change 
   
                     //the width and height accordingly
   
       {
           if(fAspectRatio > 1 ) //width is more than height 
   
           {
               //Make width as constant and calculate Height
   
               lWidth = X_MINIATUREFRAME;
               lHeight = (long)((float)Y_MINIATUREFRAME / fAspectRatio);
   
           }
           else //width is less than height(or equal to height)
   
           {
               //Make Height as constant and calculate Width
   
               lHeight = Y_MINIATUREFRAME;
               lWidth = (long)((float)X_MINIATUREFRAME * fAspectRatio);
           }
       }
   

6. Create a Memory DC compatible to WindowDC

       memDC=::CreateCompatibleDC(dc); 
   

7. Create a bitmap compatible to Window DC

       bitmap = ::CreateCompatibleBitmap(dc,lWidth,lHeight);
   

8. Select the bitmap into the Mem DC

       ::SelectObject(memDC,bitmap);
   

9. Paint the background of the DC to White

       SetBackColorToWhite(memDC);
   

10. Now play the enhanced metafile into the memory DC; ignore its return value it may be false even if successful

        PlayEnhMetaFile(memDC,hemf,&rect);    
        DWORD dwRet = GetLastError();
    

11. Create logical palette if device support a palette

        HPALETTE pal;
        if( GetDeviceCaps(dc,RASTERCAPS) & RC_PALETTE )
        {
            UINT nSize = sizeof(LOGPALETTE) + (sizeof(PALETTEENTRY) * 256);
            LOGPALETTE *pLP = (LOGPALETTE *) new BYTE[nSize];
            pLP->palVersion = 0x300;
    
            pLP->palNumEntries = 
                GetSystemPaletteEntries( dc, 0, 255, pLP->palPalEntry );
    
            // Create the palette
    
            pal = ::CreatePalette(pLP );
    
            delete[] pLP;
        }
    

12. Convert the bitmap to a DIB (refer to the download for full source code)

        HANDLE hDIB = DDBToDIB( bitmap, BI_RGB, pal );
    

13. Write DIB to file (refer to the download for full source code)

        WriteDIB((char*)strBMPFile, hDIB );
    

14. Clean up. Destroy the window and return true

        DeleteEnhMetaFile( hemf );
        ::DestroyWindow(hWnd);
    

Bitmap to EMF

I have added a new functionality of converting the BMP to EMF. Following is the step by step process for converting a BMP file to EMF File. This code is based on the comment submitted by Gernot Frisch

1. Load the bitmap from file to get the bitmap handle

       hBmp = (HBITMAP*)::LoadImage(NULL,pszBMPFile,IMAGE_BITMAP,0,0, 
               LR_CREATEDIBSECTION|LR_LOADFROMFILE);

2. Get the BITMAP structure to get the bmp's height and width

       GetObject(hBmp, sizeof(BITMAP), &bm );

3. Create MemDC

       hdcMem =::CreateCompatibleDC(GetDC(NULL));

4. Select the BMP into the DC

       SelectObject(hdcMem, hBmp);

5. Create EMF and get the emf DC

       HDC emfdc = CreateEnhMetaFile(hdcMem, pszEMFFile, NULL, 
             "Created by Pravarakhya");
   

6. Blit from BMF DC to EMF DC

       BitBlt(emfdc,0, 0, bm.bmWidth, bm.bmHeight, hdcMem, 0, 0, SRCCOPY);
   

7. Close the EMF file

       ::CloseEnhMetaFile(emfdc);
   

Points of Interest

Converting a vector format to raster format has a lot of advantages, one of them is that the image can be used over the web when it is converted to JPG or GIF. One more advantage is that the vector images can be scaled down without losing the quality. So any huge EMF can be brought down to a miniature thumbnail image which can be used over web. In our earlier project, we wanted to create a thumbnail of huge Visio Diagrams (of around 4000 sq inches!), when we saved the diagram as 100X100 pixels bitmap, we were losing quality and image was not acceptable. We then found this solution of saving the diagram as EMF and then scaling it down to 100X100 pixels bitmap. This miniature is as good as its bigger one without any loss of quality.

History

• 18 Oct 2003 - Version 1.0 Initial Release
• 24 Oct 2003 - Version 2.0
  • Removed the Window Creation code (Thanks to Paolo Messina)
  • Added the BMP to EMF functionality (Thanks to Gernot Frisch )

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The following code will convert from all formats (including emf) to anything except emf and wmf. Keith Yerian 5:00 25 May '08   Public Shared Sub Convert(ByVal FromSpec As String, ByVal IntoSpec As String) Dim Pic As New PictureBox: Pic.Image = System.Drawing.Image.FromFile(FromSpec,True) Pic.Image.Save(IntoSpec) End Sub Note: 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. Saving the image to the same file it was constructed from is not allowed and throws an exception. Keith Alan Yerian Sign In·View Thread·PermaLink Re: Also - if you wish to resize during the conversion.... Keith Yerian 5:06 25 May '08   Public Shared Sub Convert(ByVal FromSpec As String, ByVal IntoSpec As String, ByVal WidthInPixels As Integer) Dim Pic As New PictureBox: Pic.Image = System.Drawing.Image.FromFile(FromSpec,True) Dim HeightInPixels As Integer = cInt(Pic.Image.Height * WidthInPixels / Pic.Image.Width) Dim TargetBounds As New Rectangle(0,0,WidthInPixels,HeightInPixels) Dim Bitmap As New Bitmap(WidthInPixels,HeightInPixels) Pic.Width = WidthInPixels Pic.Height = HeightInPixels Pic.SizeMode = PictureBoxSizeMode.StretchImage Pic.DrawToBitmap(BitMap, TargetBounds) Bitmap.Save(IntoSpec) End Sub Keith Alan Yerian Sign In·View Thread·PermaLink In lieu of email... Hal Berman 11:09 7 Dec '07   I can't find an email address for you so I can't send you an email to say that I'm using this utility in a commercial application as the source code requests. So, I'll say thank you here and just mention that I'm using the code in an ActiveX control so that I can save an enhanced metafile that's on the clipboard to a bitmap file. Sign In·View Thread·PermaLink ConvertEMFtoBMP fails on Windows XP with mono colored EMF Rico Sinnig 9:08 26 Jun '05   first message was faulty, look to reply message Sign In·View Thread·PermaLink the diagnosis was to fast and wrong Rico Sinnig 9:36 26 Jun '05   sorry, the problem didn't depend on my dualmonitor configuration neverthless I had to change the code, to get a valid "pal" variable: ConvertEMFToBMP.cpp line 356 to 369 // if( GetDeviceCaps(dc,RASTERCAPS) & RC_PALETTE ) // { if body code ... // } it seems to be needed, even if the EMF is mono colored. Sign In·View Thread·PermaLink Re: the diagnosis was to fast and wrong Pravarakhya 10:25 26 Jun '05   Hi, Thank you for informing this to me. Let me check the code and make the changes accordingly. Pravar My Image Processing Article! Rate it!! Sign In·View Thread·PermaLink bitmap = :: CreateCompatibleBitmap(dc,lWidth,lHeight); Ziggy Short 6:55 21 Feb '05   I'm getting a problem with "not enough memory" ERROR_NOT_ENOUGH_MEMORY being returned for CreateCompatibleBitmap. Is there a work around? Can I limit the number of colours? Sign In·View Thread·PermaLink 1.36/5 (6 votes) EMF to WMF conversion Sanjay Saini 8:02 14 Feb '05   I have developed a program for converting EMF to WMF format. But the converted file is not opening up in Centura Team Builder. Working fine with windows. Pls help. Sign In·View Thread·PermaLink 1.33/5 (2 votes) why the picture I converted from bmp is not more legible tongji_2002 1:58 27 Sep '04   I think the emf files is smaller and more legible than bmp files,so I want to convert a bmp file to a emf file.But I did not get a more legible picture with emf format,and the file has a same length with the source file (bmp).Is somebody tell why? Sign In·View Thread·PermaLink Re: why the picture I converted from bmp is not more legible Pravarakhya 12:18 28 Sep '04   1. Emf files can only be as legible as their original bmp files. its the bmp information only that is converted to emf, so the legibility is same. 2. Emf is not a compressed file format, so you should not expect a less file size. If you are looking for a more legible image with less file size you should go for image enhancement and compression algorithms which are actually image processing techiniques instead of looking for format conversion. Hope I have answered your questions. Pravar Pravar My Image Processing Article! Rate it!! Sign In·View Thread·PermaLink Re: why the picture I converted from bmp is not more legible tongji_2002 17:19 28 Sep '04   Thank you very much for your answering my question.Now I know the point. Somebody told me that emf is a more legible format.But now I know it is wrong. But I suspose if I save the data in the screen to a emf file in the beginning as I saved to a bmp file,is it more legible? I will try. Thank you. Sign In·View Thread·PermaLink I confuse why the picture I converted from bmp is not more legible? tongji_2002 1:56 27 Sep '04   I think the emf files is smaller and more legible than bmp files,so I want to convert a bmp file to a emf file.But I did not get a more legible picture with emf format,and the file has a same length with the source file (bmp).Is somebody tell why? Sign In·View Thread·PermaLink Resize a metafile Doron Ben-Ari 9:48 9 Sep '04   If I have a metafile which is bigger then one page, and I want to programmatically resize it to fit into the page.... how do I do this (assuming I know the resulting page size or have some kind of %zoom in mind). Thanks ! Sign In·View Thread·PermaLink 1.00/5 (2 votes) Re: Resize a metafile Pravarakhya 2:38 10 Sep '04   a metafile is a vector image and can be played onto any size that you specify. since a metafile doesnt hold any size information there is no question of resizing a metafile. To answer your question, just use PlayEnhMetafile and specify your page size. Pravar Sign In·View Thread·PermaLink bmp to dxf file Tapas Mondal 20:57 17 Aug '04   Is there any possibility to do this. With Regards, tapas Tapas Mondal contact tapasmondal@lycos.com Sign In·View Thread·PermaLink Re: bmp to dxf file Pravarakhya 7:29 19 Aug '04   I have no idea about dxf file Tapas! Thanks and Regards, Pravarakhya My Image Processing Article! Rate it!! Sign In·View Thread·PermaLink Please Rate my Article Pravarakhya 5:36 4 May '04   If you like it, please rate it Thanks and Regards, Pravarakhya Sign In·View Thread·PermaLink BMP->WMF is it possible ? SP6NIN 3:05 30 Apr '04   Is it possible to add some modification to BMP->EMF code, to get the conversion from BMP to WMF (placeble format)? I would like to have a possibility to create a WMF file in similar manner as EMF file and/or copy the WMF to clipboard. I have no sufficient GDI & C++ knowledge to do it myself. But I was able to adapt the Pravarakhya's idea into my CA-Visual Objects and I was very satisfied that I could transform C++ code into my language. Thank you Pravarakhya for your valuable stuff. Regards, Marek Sign In·View Thread·PermaLink 3.50/5 (2 votes) BMP->EMF Locked EMF, DeleteEnhMetaFile SP6NIN 2:56 30 Apr '04   During some tests I found that after CloseEnhMetaFile(), the created EMF file is locked and can not be deleted. When I created another EMF file, then both file were locked, etc. The files could be unlocked and deleted only when the whole application is closed. I found in WIN SDK the following information: ---------------- When the application no longer needs the enhanced metafile handle, it should release the handle by calling the DeleteEnhMetaFile function. ---------------- So I added DeleteEnhMetaFile() and now the file is not locked and can be deleted soon after creation. I hope this information will be usefull, Regards, Marek Sign In·View Thread·PermaLink 4.00/5 (1 vote) WIN98, BMP->EMF, error 2 in CreateEnhMetaFile SP6NIN 0:41 30 Apr '04   Hello, I tried BMP->EMF converting and it works for W2K and XP. I could not reach success in WIN98, only. I receive null pointer from CreateEnhMetaFile(). The GetLastErorr() gives the error code = 2. It means ERROR_FILE_NOT_FOUND. I've noticed also a GDI memory leak in WIN98, which is caused probably with the above error. I am not an expert in GDI or C++. So, I am unable to resolve it myself. I hope that somebody can help me. Marek Sign In·View Thread·PermaLink Leak resource in win98 anhsl 15:38 17 Mar '04   I have a problem when read EMF file to a image list control. It work good in Win2K/XP, but in Win98, it cause leak resource. It is because the PlayEnhMetaFile funtion but I can not find any replacement Can you help me Thank in advance Do Tuan Anh Sign In·View Thread·PermaLink Showing a bmp in a rectangle Anonymous 0:19 16 Mar '04   Hello, I could create a transparent image from a edit box content and show it in a frame, but it exeeds to out of that frame while edit box content is too large. So i need to controll that bmp only in that frame. How i can show it inside that frame by propotionally change the height and width of that bmp. If you have any idea or refference please maile me ranjithepost@yahoo.co.in Thanks in advance Ranjith Sign In·View Thread·PermaLink Re: Showing a bmp in a rectangle Pravarakhya 5:15 18 Mar '04   You can resize the bitmap with many of the image processing libraries like CxImage. Take care while you resize your bitmaps, since yours is a bitmap containing text, the text could be lost if you resize the image. Thanks and Regards, Pravarakhya Sign In·View Thread·PermaLink Good Article! anud 3:56 27 Oct '03   Really good article! Anurag Sign In·View Thread·PermaLink BMP to EMF - if anyone is interested... Gernot Frisch 21:43 20 Oct '03   bool MakeFromBMP(BITMAP* bmp) { HBITMAP handle; HDC hdcMem; hdcMem =::CreateCompatibleDC(GetDC(NULL)); handle = ::CreateBitmapIndirect(bmp); SelectObject(hdcMem, handle); HDC emfdc = CreateEnhMetaFile(NULL, NULL, NULL, "EMF\0..\0\0"); BitBlt(emfdc, 0, 0, bmp->bmWidth, bmp->bmHeight, hdcMem, 0, 0, SRCCOPY); this->m_Meta = ::CloseEnhMetaFile(emfdc); return true; } Sign In·View Thread·PermaLink 4.63/5 (5 votes)

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