Why the Bitmap.MakeTransparent() changes the PixelFormat ?

[Sharon]

Hello Experts,

I'm creating a bitmap object like this:
Bitmap myImage = new Bitmap(1024, 1024,
System.Drawing.Imaging.PixelFormat.Format24bppRgb) ;

But when I invoking the function myImage .MakeTransparent() (with or without
parameters), the myImage.PixelFormat changes to Format32bppArgb.

Why is that and how can I avoid it but still making the Bitmap transparent ?
----------
Thakns
Sharon

[Bob Powell [MVP]]

The 24bpp pixel format doesn't define transparency (Alpha) and so the system
automatically changes to a format that can express the transparent value.

There is no way to display a 24bpp image with transparency on a per-pixel
basis.

--
Bob Powell [MVP]
Visual C#, System.Drawing

Ramuseco Limited .NET consulting
http://www.ramuseco.com

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http://www.bobpowell.net/tipstricks.htm

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"Sharon" <Sh*****@newsgroups.nospam> wrote in message
news:1A**********************************@microsof t.com...

Hello Experts,

I'm creating a bitmap object like this:
Bitmap myImage = new Bitmap(1024, 1024,
System.Drawing.Imaging.PixelFormat.Format24bppRgb) ;

But when I invoking the function myImage .MakeTransparent() (with or
without
parameters), the myImage.PixelFormat changes to Format32bppArgb.

Why is that and how can I avoid it but still making the Bitmap transparent
?
----------
Thakns
Sharon

[TerryFei]

Hi Sharon,
Generally speaking, 24bit only includes RGB (three colors), not include
alpha value. So it can't produce transparent effect. I think this is the
reason when invoking the function MakeTransparent(), the PixelFormat
changes to Format32bppArgb. Because it will need alpha value(8 bits) to
generate transparent effect.
Best Regards,

Terry Fei [MSFT]
Microsoft Community Support
Get Secure! www.microsoft.com/security

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Hello Experts,

I'm creating a bitmap object like this:
Bitmap myImage = new Bitmap(1024, 1024,
System.Drawing.Imaging.PixelFormat.Format24bppRgb );

But when I invoking the function myImage .MakeTransparent() (with or withoutparameters), the myImage.PixelFormat changes to Format32bppArgb.

Why is that and how can I avoid it but still making the Bitmap transparent ?

----------
Thakns
Sharon