GDI+: Converting a BMP Image to a PNG Image

[José Roca]

 

Converting a BMP Image to a PNG Image

To save an image to a disk file, call the GdipSaveImageToFile function. The following console application loads a BMP image from a disk file, converts the image to the PNG format, and saves the converted image to a new disk file.

C++

Code Select Expand


#include <windows.h>
#include <gdiplus.h>
#include <stdio.h>
using namespace Gdiplus;

INT GetEncoderClsid(const WCHAR* format, CLSID* pClsid);  // helper function

INT main()
{
   // Initialize GDI+.
   GdiplusStartupInput gdiplusStartupInput;
   ULONG_PTR gdiplusToken;
   GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

   CLSID   encoderClsid;
   Status  stat;
   Image*   image = new Image(L"Bird.bmp");

   // Get the CLSID of the PNG encoder.
   GetEncoderClsid(L"image/png", &encoderClsid);

   stat = image->Save(L"Bird.png", &encoderClsid, NULL);

   if(stat == Ok)
      printf("Bird.png was saved successfully\n");
   else
      printf("Failure: stat = %d\n", stat);

   delete image;
   GdiplusShutdown(gdiplusToken);
   return 0;
}


PowerBASIC

The main function relies on the helper function GdiPlusGetEncoderClsid to retrieve the guid of the PNG encoder.

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' ========================================================================================
' Helper function to retrieve the encoder's clsid
' * strMimeType = Mime type (ANSI string)
' ========================================================================================
FUNCTION GdiPlusGetEncoderClsid (BYVAL strMimeType AS STRING) AS STRING

   LOCAL hr AS LONG
   LOCAL pImageCodecInfo AS ImageCodecInfo PTR
   LOCAL numEncoders AS DWORD
   LOCAL nSize AS DWORD
   LOCAL i AS LONG
   LOCAL wstrlen AS LONG
   LOCAL sMimeType AS STRING

   hr = GdipGetImageEncodersSize(numEncoders, nSize)
   REDIM buffer(nSize - 1) AS BYTE
   pImageCodecInfo = VARPTR(buffer(0))
   hr = GdipGetImageEncoders(numEncoders, nSize, BYVAL pImageCodecInfo)
   IF hr = 0 THEN
      FOR i = 1 TO numEncoders
         wstrlen = lstrlenW(BYVAL @pImageCodecInfo.MimeType)
         IF wstrlen THEN sMimeType = ACODE$(PEEK$(@pImageCodecInfo.MimeType, wstrlen * 2))
         IF INSTR(UCASE$(sMimeType), UCASE$(strMimeType)) THEN
            FUNCTION = GUIDTXT$(@pImageCodecInfo.Clsid)
            EXIT FOR
         END IF
         INCR pImageCodecInfo       '// Increments pointer
      NEXT
   END IF

END FUNCTION
' ========================================================================================


Code Select Expand


#COMPILE EXE
#DIM ALL
#INCLUDE "GDIPLUS.INC"
#INCLUDE "GDIPUTILS.INC"

' ========================================================================================
' Main
' ========================================================================================
FUNCTION PBMAIN

   LOCAL hStatus AS LONG
   LOCAL token AS DWORD
   LOCAL StartupInput AS GdiplusStartupInput
   LOCAL EncoderClsid AS GUID
   LOCAL pImage AS DWORD
   LOCAL eps AS EncoderParameters
   LOCAL ep AS EncoderParameter
   LOCAL nWidth AS DWORD
   LOCAL nHeight AS DWORD
   LOCAL transformation AS DWORD
   LOCAL strFileName AS STRING

   ' // Initialize GDI+
   StartupInput.GdiplusVersion = 1
   hStatus = GdiplusStartup(token, StartupInput, BYVAL %NULL)
   IF hStatus THEN
      PRINT "Error initializing GDI+"
      EXIT FUNCTION
   END IF

   strFileName = UCODE$("Shapes.bmp")
   hStatus = GdipLoadImageFromFile(STRPTR(strFileName), pImage)

   ' // Get the CLSID of the PNG encoder.
   EncoderClsid = GUID$(GdiPlusGetEncoderClsid("image/png"))

   ' // Save the image.
   strFileName = UCODE$("Shapes.png")
   hStatus = GdipSaveImageToFile(pImage, STRPTR(strFileName), EncoderClsid, BYVAL %NULL)
   IF hStatus = %StatusOk THEN
      PRINT "Shapes.png saved successfully"
   ELSE
      PRINT "Attempt to save Shapes.png failed"
   END IF

   ' // Cleanup
   IF pImage THEN GdipDisposeImage(pImage)

   ' // Shutdown GDI+
   GdiplusShutdown token

   WAITKEY$

END FUNCTION
' ========================================================================================