Save HICON as a png

Question

I am using IShellItemImageFactory to extract the icon for a file. I was able successfully extract it and show it in a dialog using SendDlgItemMessage(hDlg,IDC_STATIC2, STM_SETIMAGE, IMAGE_ICON, (LPARAM)hicon);

see the output: click here

The issue is when I am saving this as a file(PNG format) using GDI+ the gradients are not preserving correcting. Find the code below that I am using.

GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
Bitmap *h = new Bitmap(256, 256, PixelFormat32bppARGB);
Graphics* g = Graphics::FromImage(copy);
HDC copyHdc = g->GetHDC();
DrawIconEx(copyHdc, 0, 0, hicon, 256, 256, 0, NULL, DI_NORMAL);
g->ReleaseHDC(copyHdc);;
CLSID   encoderClsid;
GetEncoderClsid(L"image/png", &encoderClsid);
h->Save(L"D:\\mynew.png", &encoderClsid, NULL);
GdiplusShutdown(gdiplusToken);

The output that i got after the extraction of a text file: click here

Can anyone help me in solving this?

Regards, Manoj

look at the gradient of the two images, the second one got some black color. — ManojMarathayil, Nov 30 '09 at 10:38

wimix · Answer 1 · 2014-04-05T19:12:24.133

This topic is rather old but I just had the same problem and spent many hours to find a solution that preserves the transparency in the PNG file.

Since the problem can be easily solved in Java...

    sun.awt.shell.ShellFolder sf = sun.awt.shell.ShellFolder.getShellFolder(file);
    ImageIcon icon = new ImageIcon(sf.getIcon(true));
    FileOutputStream bos = new FileOutputStream("d:\\icons\\icon.png");
    ImageIO.write((BufferedImage)icon.getImage(), "PNG", bos);

... I took a look a the JDK source code. In file "\jdk\src\windows\native\sun\windows\ShellFolder2.cpp" in function "Java_sun_awt_shell_Win32ShellFolder2_getIconBits", I found the valuable hint I needed.

This function retrieves the color bitmap from the HICON and calls GetDIBits to get the image data. It's not nessesary to draw the icon - whereby the transpacency would be lost anyway.

Thank you very much, JDK developers.

This is the code I end up with:

static CLSID g_pngClsid = GUID_NULL;

// http://msdn.microsoft.com/en-us/library/windows/desktop/ms533843(v=vs.85).aspx
extern int GetEncoderClsid(const WCHAR* format, CLSID* pClsid);

static HICON getShellIconByIndex(int shilsize, int iImage)
{
    IImageListPtr spiml;
    SHGetImageList(shilsize, IID_PPV_ARGS(&spiml));

    HICON hico;
    spiml->GetIcon(iImage, ILD_TRANSPARENT, &hico);
    return hico;
}

static HICON getShellIcon(int shilsize, const std::wstring& fname) {
    UINT flags = SHGFI_SYSICONINDEX;
    SHFILEINFO fi = {0};
    HICON hIcon = NULL;

    if (SHGetFileInfo(fname.c_str(), 0, &fi, sizeof(fi), flags) != 0) {
        hIcon = getShellIconByIndex(shilsize, fi.iIcon);
    }

    return hIcon;
}

struct BITMAP_AND_BYTES {
    Gdiplus::Bitmap* bmp;
    int32_t* bytes;
};

static BITMAP_AND_BYTES createAlphaChannelBitmapFromIcon(HICON hIcon) {

    // Get the icon info
    ICONINFO iconInfo = {0};
    GetIconInfo(hIcon, &iconInfo);

    // Get the screen DC
    HDC dc = GetDC(NULL);

    // Get icon size info
    BITMAP bm = {0};
    GetObject( iconInfo.hbmColor, sizeof( BITMAP ), &bm );

    // Set up BITMAPINFO
    BITMAPINFO bmi = {0};
    bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    bmi.bmiHeader.biWidth = bm.bmWidth;
    bmi.bmiHeader.biHeight = -bm.bmHeight;
    bmi.bmiHeader.biPlanes = 1;
    bmi.bmiHeader.biBitCount = 32;
    bmi.bmiHeader.biCompression = BI_RGB;

    // Extract the color bitmap
    int nBits = bm.bmWidth * bm.bmHeight;
    int32_t* colorBits = new int32_t[nBits];
    GetDIBits(dc, iconInfo.hbmColor, 0, bm.bmHeight, colorBits, &bmi, DIB_RGB_COLORS);

    // Check whether the color bitmap has an alpha channel.
        // (On my Windows 7, all file icons I tried have an alpha channel.)
    BOOL hasAlpha = FALSE;
    for (int i = 0; i < nBits; i++) {
        if ((colorBits[i] & 0xff000000) != 0) {
            hasAlpha = TRUE;
            break;
        }
    }

    // If no alpha values available, apply the mask bitmap
    if (!hasAlpha) {
        // Extract the mask bitmap
        int32_t* maskBits = new int32_t[nBits];
        GetDIBits(dc, iconInfo.hbmMask, 0, bm.bmHeight, maskBits, &bmi, DIB_RGB_COLORS);
        // Copy the mask alphas into the color bits
        for (int i = 0; i < nBits; i++) {
            if (maskBits[i] == 0) {
                colorBits[i] |= 0xff000000;
            }
        }
        delete[] maskBits;
    } 

    // Release DC and GDI bitmaps
    ReleaseDC(NULL, dc); 
    ::DeleteObject(iconInfo.hbmColor);
    ::DeleteObject(iconInfo.hbmMask); 

    // Create GDI+ Bitmap
    Gdiplus::Bitmap* bmp = new Gdiplus::Bitmap(bm.bmWidth, bm.bmHeight, bm.bmWidth*4, PixelFormat32bppARGB, (BYTE*)colorBits);
    BITMAP_AND_BYTES ret = {bmp, colorBits};

    return ret;
}

static void saveFileIconAsPng(int shilsize, const std::wstring& fname, const std::wstring& pngFile) {
    HICON hIcon = getShellIcon(shilsize, fname);
    BITMAP_AND_BYTES bbs = createAlphaChannelBitmapFromIcon(hIcon);

    IStream* fstrm = NULL;
    SHCreateStreamOnFile(pngFile.c_str(), STGM_WRITE|STGM_CREATE, &fstrm);
    bbs.bmp->Save(fstrm, &g_pngClsid, NULL);
    fstrm->Release();

    delete bbs.bmp;
    delete[] bbs.bytes;
    DestroyIcon(hIcon);
}

Example invokation:

GdiplusStartup(...);
GetEncoderClsid(L"image/png", &g_pngClsid);

wstring fname = L"d:\\index.html";
wstring pngFile = L"d:\\icons\\index.html.png";
saveFileIconAsPng(SHIL_JUMBO, fname, pngFile);

GdiplusShutdown(...);

score 2 · Accepted Answer · answered Nov 30 '09 at 21:12

I'm missing the 'copy' from your code:

Graphics* g = Graphics::FromImage(copy);

Looking at the images it appears that the device context you're drawing the icon to doesn't have 32-bit colors (alpha channel is missing).

Try creating a DC like this:

HDC hDC = CreateCompatibleDC(NULL);

and then select a 32-bit colored (empty) bitmap into that dc. After that you can draw the icon and save it.

Save HICON as a png

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