System.Drawing.Bitmap alpha -- c#

c# : System.Drawing.Bitmap alpha

instruo
1/20/2005 11:25:02 PM

I'm using the System.Drawing.Bitmap class for loading a 32-bit bmp file which
includes an alpha channel.

The problem is, when it gets loaded (just using the Bitmap(string filename)
constructor), it doesn't bother bringing the alpha along with it. All of the
pixels just show "255" as their alpha value and Bitmap.IsAlphaPixelFormat()
returns false.

I know that the alpha does exist physically and has worked with this exact
image in other contexts. So, does anyone know how I can make Bitmap behave

Erik Molenaar
1/21/2005 11:20:24 AM

..png Bitmaps use the alpha channel

I encountered no problems using them in my projects.

Erik

"instruo" <instruo@discussions.microsoft.com> schrieb im Newsbeitrag
news:90CCB48F-4F1C-4669-BCE5-671AD782BCDF@microsoft.com...
[quoted text, click to view]

Steve McLellan
1/21/2005 11:53:00 AM

Hi,

Try posting this in the framework.drawing NG as Bob Powell is the resident
master on all things in the Drawing namespace.

Steve

[quoted text, click to view]

Mick Doherty
1/21/2005 12:04:58 PM

Basicly, a new Bitmap object is 24BPP which is why you lose the Alpha
content.
Draw the bitmap directly to a controls graphics object and you should have
no problems with Alpha, but when you manipulate the bitmap in a Memory
Bitmap the Alpha is lost. What you must do to overcome this issue, is create
the memory bitmap via a BitmapData object.

Whilst the example at the following link is for a 32bit Icon, it will give
you the solution to your problem.
http://dotnetrix.co.uk/misc.html --> Get Alpha Bitmap from 32 bit Icon.

--
Mick Doherty
http://dotnetrix.co.uk/nothing.html

[quoted text, click to view]

Got something to say? Click here to post a reply to this thread.

Don't see what you're looking for? Try a search.

View other messages about c#

View Other Months
June 2003
July 2003
August 2003
September 2003
October 2003
November 2003
December 2003
January 2004
February 2004
March 2004
April 2004
May 2004
June 2004
July 2004
August 2004
September 2004
October 2004
November 2004
December 2004
January 2005
February 2005
March 2005
April 2005
May 2005
June 2005
July 2005
August 2005
September 2005
October 2005
November 2005
December 2005
January 2006
February 2006
March 2006
April 2006
May 2006
June 2006
July 2006
August 2006
September 2006
October 2006
November 2006
December 2006
January 2007
February 2007
March 2007
April 2007
May 2007
June 2007
July 2007
August 2007
September 2007
October 2007
November 2007
December 2007
January 2008
February 2008
March 2008
April 2008

home · blog · groups

Questions? Comments? Contact the dn