Sven Neumann schreef:
> Hi,
> On Mon, 2008-12-29 at 09:56 +0100, Roel Schroeven wrote:
>> I have some BMP-files that GIMP doesn't load correctly; GIMP shows
>> almost the whole image as transparent instead of the real image data.
>> Only a small region is visible, and even that with partial transparency.
>> The image doesn't contain any transparency though (I don't even think
>> BMP supports transparency).
>> Other image editors and viewers such as Irfanview and Paint.NET open the
>> image correctly.
> I am not so sure about that. The image opened in GIMP has all the
> information and an alpha channel. If you change the alpha channel to be
> all opaque, then you will see the image as shown by other viewers you
> tried. So I would rather assume that the other viewers don't support
> masks in BMP files and just ignore that extra information. As long as
> that is not sorted out, you should not file this as a bug report against
> GIMP. It is quite likely that the bug is elsewhere.

The image is a screenshot that I make using this simple Win32/VCL code:

// Graphics::TBitmap is a Borland VCL wrapper around a Windows bitmap
void CaptureFromDC(HDC hDcSource, TRect Rect, Graphics::TBitmap *Bitmap)
  Bitmap->Width = Rect.Width();
  Bitmap->Height = Rect.Height();
  Bitmap->HandleType = bmDIB;

  if (!BitBlt(Bitmap->Canvas->Handle,
              0, 0,
              Rect.Width(), Rect.Height(),
    throw ECaptureError();

I can easily convert the bitmap to 24 bits, and then the image looks
good in GIMP, which is to be expected since it doesn't contain any alpha
information anymore. And it has the added benefit that the image files
are smaller.

Either way it's no big deal to me. I only wonder exactly where the alpha
values come from, but I guess that's more a question for a win32
programming mailing list.

The saddest aspect of life right now is that science gathers knowledge
faster than society gathers wisdom.
  -- Isaac Asimov

Roel Schroeven

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