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Conversion of Enhanced Metafile to Bitmap and viceversa

, 23 Oct 2003
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An article on conversion of EMF file to Bitmap file format and BMP to EMF

Sample Image - ConvertEMFToBMP.jpg

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 )

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Pravarakhya
Web Developer
United States United States
Pravarakhya is from Hyderabad,India and has completed 27 revolutions round the sun! His main interests include .net and MFC/VC++/COM programming. He is also interested in various design methodologies and agile methods.

Comments and Discussions

 
QuestionRegarding porting this code to Android Pinmembersunneversets5-Nov-11 1:50 
Generaldevice doesn't support a palette Pinmemberdeb200529-Nov-10 7:11 
GeneralThe following code will convert from all formats (including emf) to anything except emf and wmf. PinmemberKeith Yerian25-May-08 4:00 
GeneralRe: Also - if you wish to resize during the conversion.... PinmemberKeith Yerian25-May-08 4:06 
GeneralIn lieu of email... PinmemberHal Berman7-Dec-07 10:09 
GeneralConvertEMFtoBMP fails on Windows XP with mono colored EMF PinmemberRico Sinnig26-Jun-05 8:08 
Unsure | :~ first message was faulty, look to reply message
Generalthe diagnosis was to fast and wrong PinmemberRico Sinnig26-Jun-05 8:36 
GeneralRe: the diagnosis was to fast and wrong PinmemberPravarakhya26-Jun-05 9:25 
General bitmap = :: CreateCompatibleBitmap(dc,lWidth,lHeight); PinmemberZiggy Short21-Feb-05 5:55 
GeneralEMF to WMF conversion PinmemberSanjay Saini14-Feb-05 7:02 
Generalwhy the picture I converted from bmp is not more legible Pinmembertongji_200227-Sep-04 0:58 
GeneralRe: why the picture I converted from bmp is not more legible PinmemberPravarakhya28-Sep-04 11:18 
GeneralRe: why the picture I converted from bmp is not more legible Pinmembertongji_200228-Sep-04 16:19 
QuestionI confuse why the picture I converted from bmp is not more legible? Pinmembertongji_200227-Sep-04 0:56 
GeneralResize a metafile PinmemberDoron Ben-Ari9-Sep-04 8:48 
GeneralRe: Resize a metafile PinmemberPravarakhya10-Sep-04 1:38 
Generalbmp to dxf file PinmemberTapas Mondal17-Aug-04 19:57 
GeneralRe: bmp to dxf file PinmemberPravarakhya19-Aug-04 6:29 
GeneralPlease Rate my Article PinmemberPravarakhya4-May-04 4:36 
QuestionBMP->WMF is it possible ? PinmemberSP6NIN30-Apr-04 2:05 
GeneralBMP->EMF Locked EMF, DeleteEnhMetaFile PinmemberSP6NIN30-Apr-04 1:56 
GeneralWIN98, BMP->EMF, error 2 in CreateEnhMetaFile PinmemberSP6NIN29-Apr-04 23:41 
GeneralLeak resource in win98 Pinmemberanhsl17-Mar-04 14:38 
GeneralShowing a bmp in a rectangle PinsussAnonymous15-Mar-04 23:19 
GeneralRe: Showing a bmp in a rectangle PinmemberPravarakhya18-Mar-04 4:15 

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