Editing an indexed PixelFormat

[Nathan Sokalski]

I have created declared a Bitmap using the following statement:

Dim bmp As New Bitmap(100, 100, PixelFormat.For mat8bppIndexed)

Because the SetPixel() method is disabled and a Graphics object cannot be
created for indexed PixelFormats, I am not sure how to edit the Bitmap. I am
assuming that there is some class or technique other than the following:

Dim bmpdata As BitmapData = bmp.LockBits(Ne w Rectangle(0, 0, bmp.Width,
bmp.Height), ImageLockMode.R eadOnly, PixelFormat.For mat8bppIndexed)
For y As Integer = 0 To bmp.Height - 1
For x As Integer = 0 To bmp.Width - 1
System.Diagnost ics.Debug.Write Line(System.Run time.InteropSer vices.Marshal.R eadByte(bmpdata .Scan0,
y * bmpdata.Stride + x))
Next
Next
bmp.UnlockBits( bmpdata)

Which is basically just directly changing the data that will be saved when
the Bitmap is saved. However, using the technique shown above can make it
require multiple steps and calculations when drawing shapes such as
ellipses. Is there a more efficient way to edit an indexed Bitmap? Thanks.
--
Nathan Sokalski
njsokalski@hotm ail.com

http://www.nathansokalski.com/

[Michael Phillips, Jr.]

Re: Editing an indexed PixelFormat

Is there a more efficient way to edit an indexed Bitmap?

If you use any of the CLR routines, you are stuck with LockBits.

If you are willing to use P-Invoke, you can avail yourself of the many GDI
routines which provide direct access to the image's memory
and allow the use of fast BitBlt and similar functions that will operate on
all image pixel formats including indexed.

Create your indexed bitmap with CreateDIBSectio n and you will have all of
the fast GDI functions at your disposal.
CreateDIBSectio n returns a pointer to the image's memory that can be
directly accessed without locking and unlocking.

You can still mix and match the managed and unmanaged image API's.
You can still benefit from the System.Drawing namespace methods.


"Nathan Sokalski" <njsokalski@hot mail.comwrote in message
news:uTspDklLIH A.2268@TK2MSFTN GP02.phx.gbl...

>I have created declared a Bitmap using the following statement:
>
Dim bmp As New Bitmap(100, 100, PixelFormat.For mat8bppIndexed)
>
Because the SetPixel() method is disabled and a Graphics object cannot be
created for indexed PixelFormats, I am not sure how to edit the Bitmap. I
am assuming that there is some class or technique other than the
following:
>
Dim bmpdata As BitmapData = bmp.LockBits(Ne w Rectangle(0, 0, bmp.Width,
bmp.Height), ImageLockMode.R eadOnly, PixelFormat.For mat8bppIndexed)
For y As Integer = 0 To bmp.Height - 1
For x As Integer = 0 To bmp.Width - 1
>
System.Diagnost ics.Debug.Write Line(System.Run time.InteropSer vices.Marshal.R eadByte(bmpdata .Scan0,
y * bmpdata.Stride + x))
Next
Next
bmp.UnlockBits( bmpdata)
>
Which is basically just directly changing the data that will be saved when
the Bitmap is saved. However, using the technique shown above can make it
require multiple steps and calculations when drawing shapes such as
ellipses. Is there a more efficient way to edit an indexed Bitmap? Thanks.
--
Nathan Sokalski
njsokalski@hotm ail.com

http://www.nathansokalski.com/

>