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Altering a bitmap pixel by pixel using an array

I've been creating bitmaps using setpixel. This is too slow. After searching the net for days, about the only thing I've learned is that the fastest way is to convert a bitmap into a byte array and alter the array instead, then convert the array back into a bitmap.

The easiest way I've found to change a bitmap into an array is:

Dim bmBytes As Byte() = DirectCast(TypeDescriptor.GetConverter(bitmapTemp).ConvertTo(bitmapTemp, GetType(Byte())), Byte())

I figured I would just study the array and learn how to alter it myself, but bmBytes is a different length from one bitmap to another despite the images having the same dimensions and bpp. What's going on here? And they don't even appear long enough, 70,000-90,000 for a 320x240, which is about 1 byte per pixel. How is a pixel assigned a 32bpp color from 1 byte???

So I'm stuck. I should point out that I'm not loading a previous image and then altering, but instead creating bitmaps from scratch based on other values. So, I don't even need to extract an array first, unless I need the header from a new bitmap? I also HAVE to assign colors using RGB values.

This article is the closest I've found regarding my need, but it involves CImage and I can't figure out how to reference the class. I'm using VB.NET4

http://www.codeproject.com/KB/graphics/Fast_Image_Manipulation.aspx

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Nasir Razzaq

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Iketh

ASKER

Ok good, but I also don't know how to modify the array correctly. The article I linked is exactly what I'm looking for, but I need the CImage class, mainly for GetPitch I assume. Do you have a link to do this using the Bitmap class instead?

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Nasir Razzaq

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Iketh

ASKER

The irony of that link is that the "...." in the first block of code is what I need an example of.

Here is what I need in C++, but this doesn't convert to VB:

    for (int i=0; i<bitmapzor.GetWidth();i++)
        for (int j=0; j<bitmapzor.GetHeight();j++)
        {
            //pointer arithmetics to find (i,j) pixel colors:
            R= *(byteptr+pitch*j+3*i);
            G= *(byteptr+pitch*j+3*i+1);
            B= *(byteptr+pitch*j+3*i+2); 

            //allter pixel G color:
            G=(int)((float)G*1.3);
            if (G>255) G=255;
            //write down the new G-Color
            *(byteptr+pitch*j+3*i+1)=G;
        }

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Iketh

ASKER

specifically *(byteptr+pitch*j+3*i)

Nasir Razzaq

>//pointer arithmetics
Pointers are not supported in .NET

Iketh

ASKER

so i'm forced to use setpixel in VB?

Nasir Razzaq

Looks like that unless you can find a Managed C++ library. I googled but could not find any.

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