Accessing the pixel data in a C# Bitmap class

[Guest]

Hi,

I'm combining the pixels from 2 Bitmap classes, one is an overlay onto the
other. I'm currentlly doing it this way, using C#:

// Copy the overlay data onto the image file.
Color OverlayPixel;
for( int i = 0; i < PngImage.Width; i++)
for( int j = 0; j < PngImage.Height; j++)
{
OverlayPixel = PngOverlay.GetPixel( i, j);
if( OverlayPixel != System.Drawing.Color.Black)
{
PngImage.SetPixel( i, j, OverlayPixel);
}
}

This works, but is horribly slow, and will get even more so when I end up
doing this on larger images.

I believe this would go significantly faster if I worked on the pixel data
directly instead of going through GetPixel & SetPixel methods. Is there a
way to get the pixel data in a Bitmap class into a byte array?

Thanks Bruce

 

[Ercan Turkarslan [MS]]

Hi Bruce,

Unfortunately, you can not access the internal bitmap structure on .NET CF.

However if you create your merged bitmap as an array, you can create a .NET
CF bitmap from that array with the following code.

byte[] bitmapData = new byte[ size ];

// Combine to bitmaps into bitmapData here

MemoryStream memStream = new MemoryStream(bitmapData);

Bitmap bmp = new Bitmap(memStream);

Thanks

Ercan

 

[Guest]

Hi Ercan,

Thanks for the reply,

That looks like a nice way to get an array of bytes into a bitmap. But
before I can do that, I need to get the pixel data out as an array of bytes
so I can effeciently merge them. The two bitmaps come from 2 *.png fies that
I load into two bitmap classes. I was hoping there was a way to extract the
bitmap data in the class into a byte array, because I really don't want to
write my own *.png file reader.

Bruce

 

[Ercan Turkarslan [MS]]

BMP formated files may be easier to work with and you may find more
information on BMP format.The array should be arranged just like a BMP file.

There is another option which requires native programming.
1) You can load bitmaps,
2) Paint them to a device context using BitBlt etc
3) Implement an inherit managed stream class which will p/invoke to some
native functions for retrieving the bitmap.

Sorry this is my last silver bullet for this problem

- Ercan