Convert 32x32 icon to 16x16

Thursday Jan 17th 2002 by Fabio Falsini
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A solution to convert an icon from 32x32 format to 16x16.

Hi, finally I had the occasion to contribute in CodeGuru site. Well, this is my humble solution to convert an icon from 32x32 format to 16x16. The procedure is very simple, I get the two bitmaps of the icon (the image bitmap and the mask bitmap) and I resize separately each bitmap from 32x32 to 16x16, with these two new bitmaps obtained from the conversion is possible to make a new 16x16 icon generated by the mother 32x32. Theorically the procedure is correct and it works well enough; however, I noticed that the conversion made by Windows obtains the best result compared with this, if anyone have an idea about to improve this algorithm any suggestion will be welcomed.

HICON Convert32x32IconTo16x16(HICON h32x32Icon)
{
  HDC hMainDC, hMemDC1, hMemDC2;
  HICON h16x16Icon;
  BITMAP bmp;
  HBITMAP hOldBmp1, hOldBmp2;
  ICONINFO IconInfo32x32, IconInfo16x16;

  GetIconInfo(h32x32Icon, &IconInfo32x32);

  hMainDC = ::GetDC(m_hWnd);
  hMemDC1 = CreateCompatibleDC(hMainDC);
  hMemDC2 = CreateCompatibleDC(hMainDC);

  GetObject(IconInfo32x32.hbmColor, sizeof(BITMAP), &bmp);

  IconInfo16x16.hbmColor = CreateBitmap( 16, 16, 
                                         bmp.bmPlanes,
                                         bmp.bmBitsPixel,
                                         NULL);

  hOldBmp1 = (HBITMAP) SelectObject( hMemDC1, 
                                     IconInfo32x32.hbmColor);
  hOldBmp2 = (HBITMAP) SelectObject( hMemDC2,
                                     IconInfo16x16.hbmColor);

  StretchBlt(hMemDC2,
       0, 0,
       16, 16,
       hMemDC1,
       0, 0,
       32, 32,
       SRCCOPY
       );

  GetObject(IconInfo32x32.hbmMask, sizeof(BITMAP), &bmp);

  IconInfo16x16.hbmMask = CreateBitmap( 16, 16, 
                                        bmp.bmPlanes, 
                                        bmp.bmBitsPixel,
                                        NULL);

  SelectObject(hMemDC1, IconInfo32x32.hbmMask);
  SelectObject(hMemDC2, IconInfo16x16.hbmMask);

  StretchBlt(hMemDC2,
             0, 0,
             16, 16,
             hMemDC1,
             0, 0,
             32, 32,
             SRCCOPY
       );

  SelectObject(hMemDC1, hOldBmp1);
  SelectObject(hMemDC2, hOldBmp2);

  IconInfo16x16.fIcon = TRUE;
  h16x16Icon = CreateIconIndirect(&IconInfo16x16);

  DeleteObject(IconInfo32x32.hbmColor);
  DeleteObject(IconInfo16x16.hbmColor);
  DeleteObject(IconInfo32x32.hbmMask);
  DeleteObject(IconInfo16x16.hbmMask);
  DeleteDC(hMemDC1);
  DeleteDC(hMemDC2);
  ::ReleaseDC(m_hWnd, hMainDC);

  return h16x16Icon;
}
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