How to display PNG / BMP images with alpha channels

Hi,

We are currently trying to display PNG / BMP images with alpha channels using the ff code. Based on the debugging info, fileinfo.Flags has FILEINFO_HAS_ALPHA and hLeadBitmap.Flags.Transparency always returns 0. The resulting image however is that the surrounding area of the image is black. I have attached a couple of files for testing.

RedirectIO(OpenPicFiles, NULL, NULL, NULL, NULL, (L_VOID *)filename) ;

Ret = FileInfo(filename, &fileinfo, sizeof(FILEINFO), 0, NULL);
if( Ret == SUCCESS && fileinfo.Flags & FILEINFO_HAS_ALPHA ){ // check to make sure that it has alpha channels
    . . .
} // if
Ret = InitBitmap(&hLeadBitmap, sizeof(BITMAPHANDLE), fileinfo.Width, fileinfo.Height, fileinfo.BitsPerPixel);
Ret = LoadBitmap(filename, &hLeadBitmap, sizeof(BITMAPHANDLE), hLeadBitmap.BitsPerPixel, hLeadBitmap.Order, NULL, NULL);
// debugging hLeadBitmap.Flags.Transparency, always returns 0

RedirectIO(NULL, NULL, NULL, NULL, NULL, NULL) ;

w_DispModeType = GetDisplayMode() ;
SetDisplayMode(DISPLAYMODE_FIXEDPALETTE|DISPLAYMODE_RESAMPLE|DISPLAYMODE_BICUBIC, DISPLAYMODE_FIXEDPALETTE|DISPLAYMODE_BICUBIC);
hpalPaint = CreatePaintPalette(dc.GetSafeHdc(), &hLeadBitmap);
if (hpalPaint)
{
SelectPalette (dc.GetSafeHdc(), hpalPaint, FALSE);
RealizePalette (dc.GetSafeHdc());
}
PaintDCEffect(dc.GetSafeHdc(), &hLeadBitmapNULL, NULL, &DrawRect, PaintRect, SRCCOPY, 0);
SetDisplayMode(DISPLAYMODE_FIXEDPALETTE|DISPLAYMODE_BICUBIC|w_DispModeType, w_DispModeType) ;

We are currently using LEADTOOLS Raster Imaging Pro version 15.0 toolkit.

We are currently using LEADTOOLS Raster Imaging Pro version 15.0 toolkit.

Can you send me the sample images that you use? If you want to attach files, make sure to put them in a ZIP or RAR file and don't use the Preview feature.
If the ZIP file is larger than 5MB, you can send your LEADTOOLS SDK serial number (do Not post it here) to support@leadtools.com and ask for FTP upload instructions.

However, the following forum post contains useful information about loading images with alpha channel:
http://support.leadtools.com/CS/forums/41815/ShowPost.aspx
 
Thanks,
Maen Badwan
LEADTOOLS Technical Support

I followed the link provided but it is in c#. I tried the online documentation for RasterPaintProperties but cannot find any related topic.

We are currently using VC++ and Raster Imaging Pro v15 toolkit.

I have also attached the image files we want to display and print.

HI,
I made some experiments using FeatherAlphaBlendBitmap() and tested the ff. code.

RedirectIO(OpenPicFiles, NULL, NULL, NULL, NULL, (L_VOID *)filename) ;

Ret = FileInfo(filename, &fileinfo, sizeof(FILEINFO), 0, NULL);
Ret = InitBitmap(&hLeadBitmap, sizeof(BITMAPHANDLE), fileinfo.Width, fileinfo.Height, fileinfo.BitsPerPixel);
Ret = LoadBitmap(filename, &hLeadBitmap, sizeof(BITMAPHANDLE), hLeadBitmap.BitsPerPixel, hLeadBitmap.Order, NULL, NULL);
// debugging hLeadBitmap.Flags.Transparency, always returns 0

RedirectIO(NULL, NULL, NULL, NULL, NULL, NULL) ;

if( Ret == SUCCESS && fileinfo.Flags & FILEINFO_HAS_ALPHA ){ // check to make sure that it has alpha channels
    Ret = GetBitmapAlpha(&hLeadBitmap, &hLeadAlpha, sizeof(BITMAPHANDLE));
    memset( &hLeadBmpPlusAlpha, 0, sizeof( hLeadBmpPlusAlpha ) ) ;
    hLeadBmpPlusAlpha.uStructSize = sizeof( hLeadBmpPlusAlpha ) ;
    Ret = FeatherAlphaBlendBitmap(&hLeadBmpPlusAlpha, 0, 0, hLeadAlpha.Width, hLeadAlpha.Height,&hLeadBitmap, 0, 0, &hLeadAlpha, 0, 0);
} // if


w_DispModeType = GetDisplayMode() ;
SetDisplayMode(DISPLAYMODE_FIXEDPALETTE|DISPLAYMODE_RESAMPLE|DISPLAYMODE_BICUBIC, DISPLAYMODE_FIXEDPALETTE|DISPLAYMODE_BICUBIC);
hpalPaint = CreatePaintPalette(dc.GetSafeHdc(), &hLeadBitmap);
if (hpalPaint)
{
SelectPalette (dc.GetSafeHdc(), hpalPaint, FALSE);
RealizePalette (dc.GetSafeHdc());
}
PaintDCEffect(dc.GetSafeHdc(), &hLeadBitmapNULL, NULL, &DrawRect, PaintRect, SRCCOPY, 0);
SetDisplayMode(DISPLAYMODE_FIXEDPALETTE|DISPLAYMODE_BICUBIC|w_DispModeType, w_DispModeType) ;

The above code however returns ERROR_NO_BITMAP at FeatherAlphaBlendBitmap(). Also, the sample program on your online documentation (http://www.leadtools.com/help/leadtools/v15/main/api/dllsteps/tuttransparency.htm) has no parameter for nXMaskShift and nYMaskShift os I passed 0.

I modified our API v15 LoadSave demo to display images with alpha channels using the L_FeatherAlphaBlendBitmap function. Note that you need to add the attached project to the following folder:
[LEADTOOLS 15 folder]\Examples\API

After this, please check the following code in the attached demo:
+------------+
case IDM_ALPHA:
if(Data.BitmapHandle.Flags.Allocated && (Data.BitmapHandle.BitsPerPixel == 32))
{
BITMAPHANDLE ForegroundBmp = {0}, AlphaBitmap = {0};
nRet = L_CopyBitmap(&ForegroundBmp, &Data.BitmapHandle, sizeof(BITMAPHANDLE));
nRet = L_FillBitmap(&Data.BitmapHandle,RGB(20, 130, 255));
nRet = L_GetBitmapAlpha(&ForegroundBmp, &AlphaBitmap, sizeof(BITMAPHANDLE));
nRet = L_FeatherAlphaBlendBitmap(&Data.BitmapHandle, 0, 0,AlphaBitmap.Width, AlphaBitmap.Height, &ForegroundBmp, 0, 0, &AlphaBitmap,0,0);
L_FreeBitmap(&ForegroundBmp);
L_FreeBitmap(&AlphaBitmap);
::InvalidateRect(hWnd, NULL, TRUE);
}
break;
+------------+

Thanks,
Maen Badwan
LEADTOOLS Technical Support

Based on your latest sample code, I was able to have a successful call of FeatherAlphaBlendBitmap(). The resulting image however is still the same, black on the surroundings.

Is the destination bitmap need to be 24 bit and not 32? According to http://support.leadtools...ums/41815/ShowPost.aspx, "By default, our paint functions do not take the alpha channel into consideration."

How do we create a 24 bit bitmap from 32 bit? Or is there a way to create a 24 bitmap specifying the height, width and bits per pixel and initializing all pixel values to RGB(255,255,255)? A sample with be of great help.

It seems that you didn't run the alpha channel code in the demo. After loading the image using the modified LoadSave demo, you need to click the "Alpha test..." menu to apply the FeatherAlphaBlend function and display the images with alpha cannel.
I am attaching a screenshot that shows how the images appear on my side after applying the L_FeatherAlphaBlendBitmap function.

If you are getting different results, please send your LEADTOOLS Raster Imaging Pro v15 serial number (do Not post it here) to support@leadtools.com and ask about the instructions to download and install the latest LEADTOOLS v15 patches.

Thanks,
Maen Badwan
LEADTOOLS Technical Support