how to take the RGB value of the selected region of the bitmap image using unsafe coding in .net

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How do I take the RGB value of the selected region of the bitmap image using unsafe coding in .net
I need to change the particular region that I have selected and giving the i and j value of the starting position of the selected image.

The entire code is

//   selection is the rectangle from the mouse selected region from the picturebox....
bitmap bmp2 = new bitmap(picturebox1.image);
bitmapdata data = bmp2.lockbits(selection,ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
unsafe
{
     byte *p = (byte*)(data.scan0);
     offset = data.stride - bmp.width*3;
     for(i=selection.x; i&lt; limitx;i++)
     {
          for(j=selection.y;j&lt;limity;j++)
          {
               position = j*bmp2.width *(3) +i*3+j*offset;//what is line used for i dot know....
               b = p [ position +j];     ///need to take the RGB value
               g = p [position+j+1];
               r = p [ position + j +2];
               p+=3;
          }
          p+=offset;
     }
}
picturebox.image = bmp2.image;   // that should display the selected region in any color....
bmp2.unlockbits(data);
bmp2.dispose();

It's not working properly.

Please help me...

Posted 3-Jan-11 17:01pm

The M A R S

Updated 3-Jan-11 22:56pm

Dalek Dave

v4

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Dalek Dave 4-Jan-11 4:56am

Edited for Grammar, Readability and Code Block.

3 solutions

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Vinayak P Kamath · Answer 1 · 2011-01-03T22:21:00

Solution 3

The code as I see does nothing to the image. Looks like if you save the rgb values that you get in the loop into an array of some structure you get the rgb values for all the pixels, thats all. The above code in itself does not do anything.
If you want to get a rectangular section as a seprate image, the you can lock bits of that rectangle and read the scan0 of that data into a bitmap.

Posted 3-Jan-11 22:21pm

Vinayak P Kamath

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The M A R S 4-Jan-11 5:24am

actually my purpose is to change the color where i selected in the huge image and repaint to another picturebox that should happen very fast so that i prefer unsafe coding as pointer
i just send the selected area as rectangle, the code should found the exact position of that image and process very quickly and returns that selected areas as different color please help me as code format...

Sergey Alexandrovich Kryukov · Answer 2 · 2011-01-03T17:25:00

Solution 1

This code will mess up things in case original bitmap pixel format is not PixelFormat.Format24bppRgb. The format should be checked up in all cases.

Despite of your intent to invert a subset of bits, this code actually invert all bits. Inverting a subset is trivial if it is a rectangle. In this case, the required rectangle should be passed as a first parameter of LockBits.

Actual update of the bitmap data is done by UnlockBits. That's why passing a rectangle of smaller size as a parameter of LockBits is always better is you want to have better performance.

This advice also valid of your subset is not rectangular. In this case, you can calculate bounding rectangle around the bits you're going to modify. If the interception of this bounding rectangle is less then the whole bitmap rectangle, you can have better performance again.

Posted 3-Jan-11 17:25pm

Sergey Alexandrovich Kryukov

Updated 4-Jan-11 7:11am

v3

Comments

Sergey Alexandrovich Kryukov 3-Jan-11 23:28pm

There is no actual question, so I decided just to report problems I can see.

The M A R S 4-Jan-11 0:17am

i tried that too as
the entire code is

// selection is the rectangle from the mouse selected region from the picturebox....
bitmap bmp2 = new bitmap(picturebox1.image);
bitmapdata data = bmp2.lockbits(selection,ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
unsafe
{
byte *p = (byte*)(data.scan0);
offset = data.stride - bmp.width*3;
for(i=selection.x; i< limitx;i++)
{
for(j=selection.y;j

Dalek Dave 4-Jan-11 4:56am

Good Answer.

Sergey Alexandrovich Kryukov 4-Jan-11 13:07pm

@9585228677:

Using a subset of a rectangular shape via passing this rectangle to LockbBts is always better. You see, actual update of bitmap data is done by the method UnlockBits; moving of data takes time, so the less the subset, the better.

Actually, let me put this in the text of my answer... please see updated Answer above.

Sergey Alexandrovich Kryukov 4-Jan-11 13:37pm

From your text I don't understand if you still have a problem.
Maybe you don't see the result of updated bitmap on screen or something?

At them moment of writing, you already received 3 answer and still say "help me", you say what you want but you never told what's exactly going wrong.

Please tell this explicitly, if you need to solve the problem.

Sergey Alexandrovich Kryukov 11-Jan-11 11:48am

It should work. Did it?

Vinayak P Kamath · Answer 3 · 2011-01-04T00:47:00

try
      {
        Bitmap bmp = new Bitmap(250, 50);
        //   selection is the rectangle from the mouse selected region from the picturebox....
        Bitmap bmp2 = new Bitmap(@"C:\Users\vinayakk\Desktop\tenant_notselected.jpg");
        BitmapData data = bmp2.LockBits(new Rectangle(0, 0, 250, 50), ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
        BitmapData dta1 = bmp.LockBits(new Rectangle(0, 0, 250, 50), ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
      
      unsafe
      {
        //byte* p = (byte*)(data.Scan0);
        //var offset = data.Stride - bmp2.Width * 3;
        //for (int i = 10; i < 50; i++)
        //{
        //  for (int j = 10; j < 50; j++)
        //  {
        //    var position = j * bmp2.Width * (3) + i * 3 + j * offset;
        //    //what is line used for i dot know....               
        //    byte b = p[position + j] = (byte)255;
        //    // need to take the RGB value              
        //    byte g = p[position + j + 1] = (byte)255; byte r = p[position + j + 2] = (byte)255; p += 3;
        //  } p += offset;
        //}
      }
      // that should display the selected region in any color....
        dta1.Scan0 = data.Scan0;
        bmp2.UnlockBits(data);
        bmp.UnlockBits(dta1);
        
        bmp.Save("--Your path.jpg--");
      bmp2.Dispose();
      }
      catch (Exception)
      {
        throw;
      }

Change the paths. Your selection is saved. Uncomment the code in the loop the pixel colors are changed.

how to take the RGB value of the selected region of the bitmap image using unsafe coding in .net

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