asked on

Foreach, Or Not Foreach.

I've got this method ..or rather series of methods that cycles through every pixel in an image using unmanaged code. One of which is displayed below ( this particular one, in conjunction with some other methods, checks a page to see if it is blank or has anything on it ).
I'd like to come up with a way to just have a template-like method stored in a .dll file, and then cycle through all the pixels using a Foreach loop on an image. For instance..

foreach(UnmanagedPixel p in iImage)
{
...
}

...Is this even possible? I've got no idea where to even begin to attempt something like this. Here's the sample method.

            public static Boolean ValidatePage(Image imgImage)
            {
                  // Store our blank pixel count
                  double dblBlankPixels = 0.0;
                  // Store our pixel count
                  double dblTotalPixels = 0.0;
                  // Work with a Bitmap copy
                  Bitmap bmImage = (Bitmap)imgImage.Clone();

                  // Lock the bits
                  BitmapData bmData = bmImage.LockBits
                        (new Rectangle(Point.Empty,bmImage.Size),
                        ImageLockMode.ReadOnly,PixelFormat.Format24bppRgb);

                  // Retrieve the Bitmap Stride Width
                  Int32 Stride = bmData.Stride;
                  // Create Unmanaged memory for this code
                  IntPtr Scan0 = bmData.Scan0;

                  unsafe
                  {
                        byte * p = (byte *)(void *)Scan0;

                        Int32 nOffset = Stride - bmImage.Width * 3;
                        Int32 nWidth = bmImage.Width * 3;

                        for(int y = 0; y < bmImage.Height; ++y)
                        {
                              for(int x=0; x < nWidth; ++x )
                              {
                                    if(p[0] >= (byte)(225))
                                    {
                                          dblBlankPixels++;
                                    }
                                    dblTotalPixels++;
                                    ++p;
                              }
                              p += nOffset;
                        }
                  }
                  // Unlock the bitmap
                  bmImage.UnlockBits(bmData);
                  // Destroy it
                  bmImage.Dispose();

                  return ComparePixelData(dblBlankPixels,dblTotalPixels);
            }

AlexFM

Not exactly what you want but possibly may help.
Consider the form with two picture boxes and button. See this code:

Bitmap m_bmp1;
Bitmap m_bmp2;

private void button1_Click(object sender, System.EventArgs e)
{
m_bmp1 = new Bitmap(@"C:\Sample.bmp");
pictureBox1.Image = m_bmp1;

m_bmp2 = new Bitmap(m_bmp1);
ChangeBitmap(m_bmp2);
pictureBox2.Image = m_bmp2;
}

void ChangeBitmap(Bitmap bmImage)
{
// Lock the bits
BitmapData bmData = bmImage.LockBits
(new Rectangle(Point.Empty,bmImage.Size),
ImageLockMode.ReadWrite,PixelFormat.Format24bppRgb);

// Retrieve the Bitmap Stride Width
Int32 Stride = bmData.Stride;
// Create Unmanaged memory for this code
IntPtr Scan0 = bmData.Scan0;

unsafe
{
byte * p = (byte *)(void *)Scan0;

Int32 nOffset = Stride - bmImage.Width * 3;
Int32 nWidth = bmImage.Width * 3;

for(int y = 0; y < bmImage.Height; ++y)
{
for(int x=0; x < nWidth; ++x )
{
p[0] = (byte)(255 - p[0]);
++p;
}
p += nOffset;
}
}
// Unlock the bitmap
bmImage.UnlockBits(bmData);
}

Simple - when button is pressed, two images are shown. Second image is inverted. But this solution is not generic - if I want to make other transformation, I need to write another ChangeBitmap function. The idea is to pass pointer to callback function (delegate) which makes single pixel conversion. See the following code:

Bitmap m_bmp1;
Bitmap m_bmp2;
delegate void ChangePixelDelegate(ref byte pixel);

private void button1_Click(object sender, System.EventArgs e)
{
m_bmp1 = new Bitmap(@"C:\Sample.bmp");
pictureBox1.Image = m_bmp1;

m_bmp2 = new Bitmap(m_bmp1);
ChangeBitmap(m_bmp2, new ChangePixelDelegate(this.ChangePixel));
pictureBox2.Image = m_bmp2;
}

void ChangePixel(ref byte pixel)
{
pixel = (byte)(255 - pixel);
}

void ChangeBitmap(Bitmap bmImage, ChangePixelDelegate callback)
{
// Lock the bits
BitmapData bmData = bmImage.LockBits
(new Rectangle(Point.Empty,bmImage.Size),
ImageLockMode.ReadWrite,PixelFormat.Format24bppRgb);

// Retrieve the Bitmap Stride Width
Int32 Stride = bmData.Stride;
// Create Unmanaged memory for this code
IntPtr Scan0 = bmData.Scan0;

unsafe
{
byte * p = (byte *)(void *)Scan0;

Int32 nOffset = Stride - bmImage.Width * 3;
Int32 nWidth = bmImage.Width * 3;

for(int y = 0; y < bmImage.Height; ++y)
{
for(int x=0; x < nWidth; ++x )
{
callback(ref p[0]);
++p;
}
p += nOffset;
}
}
// Unlock the bitmap
bmImage.UnlockBits(bmData);
}

Now I can write another function (for example, ChangeBrightness):

void ChangeBrightness(ref byte pixel)
{
int n = pixel + 20;
if ( n > 255 )
n = 255;
pixel = (byte)n;
}

and call the same ChangeBitmap function providing another callback:

ChangeBitmap(m_bmp2, new ChangePixelDelegate(this.ChangeBrightness));

This is basic idea, implementation details may be improved.