Not able to successfully use lockbits

Question

Hi i m really new in image processing in C# and the code below basically getpixel from the image I browsed from my computer and will compare the RGB value of the pixel with the right pixel and if its the same value, it will setpixel to cyan color. the problem is with the getpixel, it is really very slow even on a small resolution photos and I'm also looking to add more function to it. I have read about lockbits and was trying it out but was unable to successfully write the code.

namespace Disimage
{
  public partial class Form1 : Form
  {
    public Form1()
    {
        InitializeComponent();
    }

    public Bitmap pic;
    public Bitmap pic2;

    private bool compare_colour_constant(int original, int sample)
    {
        if (original == sample)
            return true;
        else
            return false;             
    }

    public void btn_browse_Click_Click(object sender, EventArgs e)
    {
        try
        {
            OpenFileDialog open = new OpenFileDialog();
            open.Filter = "Image Files(*.jpg; *.jpeg; *.gif; *.bmp)|*.jpg; *.jpeg; *.gif; *.bmp";
            if (open.ShowDialog() == DialogResult.OK)
            {
                pic = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);
                pic2 = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);

                //pictureBox1.Image = new Bitmap(open.FileName);
                pic = new Bitmap(open.FileName);
                pic2 = new Bitmap(open.FileName);
                pictureBox1.Image = pic;
                pictureBox2.Image = pic2;
                pictureBox1.SizeMode = System.Windows.Forms.PictureBoxSizeMode.StretchImage;
                textBox1.Text = open.FileName;
                pictureBox2.SizeMode = System.Windows.Forms.PictureBoxSizeMode.StretchImage;                        
            }
        }
        catch (Exception)
        {
            throw new ApplicationException("Failed loading image");
        }
    }


    public void scan_Click(object sender, EventArgs e)
    {
        try
        {
            //Bitmap pic = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);
            //Bitmap pic2 = new Bitmap(Width, Height, PixelFormat.Format24bppRgb);

            pictureBox1.Image = pic;
            pictureBox2.Image = pic2;
            progressBar1.Minimum = 0;
            progressBar1.Maximum = pic.Width;
            int []RGB = pic.GetPixel();

                for (int w = 1; w < pic.Width - 1; w++)
                {
                    progressBar1.Step = 1;
                    progressBar1.PerformStep();

                    if (progressBar1.Value == progressBar1.Maximum)                  
                        progressBar1.Value = 0;

                    for (int h = 1; h < pic.Height - 1; h++)
                    {
                        int red = pic.GetPixel(w, h).R;
                        int green = pic.GetPixel(w, h).G;
                        int blue = pic.GetPixel(w, h).B;
                        int colour = pic.GetPixel(w, h).R + pic.GetPixel(w, h).G + pic.GetPixel(w, h).B;
                        int colour2 = pic.GetPixel(w + 1, h).R + pic.GetPixel(w + 1, h).G + pic.GetPixel(w + 1, h).B;

                        /*textBox2.Text = red.ToString();
                        textBox3.Text = green.ToString();
                        textBox4.Text = blue.ToString();
                        */

                        int Lred = pic.GetPixel(w - 1, h).R;
                        int Lgreen = pic.GetPixel(w - 1, h).G;
                        int Lblue = pic.GetPixel(w - 1, h).B;

                        int Rred = pic.GetPixel(w + 1, h).R;
                        int Rgreen = pic.GetPixel(w + 1, h).G;
                        int Rblue = pic.GetPixel(w + 1, h).B;

                        if (compare_colour_constant(colour, colour2) == true)
                            pic2.SetPixel(w, h, Color.Cyan);
                    }
                }
        }            
        catch (Exception)
        {
            throw new ApplicationException("Failed loading image");
        }
    }
}

}

Answer 1

Though a little late, I'd be happy to answer your question for other users. The first thing you would need to do is to declare a BitmapData variable, which would hold (obviously) the data from the Bitmap image that has been placed into the memory. To do this:

System.Drawing.Imaging.BitmapData bmpdata = pic.LockBits(new Rectangle(pictureBox1.Location.X, pictureBox1.Location.Y, pictureBox1.Width, pictureBox1.Height),  
System.Drawing.Imaging.ImageLockMode.ReadWrite,  
System.Drawing.Imaging.PixelFormat);

After calling this code, you can proceed to edit the BitmapData to your liking. In this situation you could call for a loop through a byte array of the Data and compare the RGB to the RGB of the pixel immediately to the right's and determine similarity. Example:

unsafe  
{  
    for (int y = 0; y < bmpdata.Height; y++) // Repeats for each row  
    {  
        byte* row = (byte*)bmpdata.Scan0 + (y * bmpdata.Stride); // Array of bytes for the current row of pixels  
        for (int x = 0; x < bmpdata.Width; x++) // Repeats for each pixel on each row  
        {  
            if (row[x * 4] == row[(x + 1) * 4] && row[(x * 4) + 1] == row[((x + 1) * 4) + 1] && row[(x * 4) + 2] == row[((x + 1) * 4) + 2])  
            {  
                row[x *  4] = 255; // Blue value of current pixel  
                row[(x * 4) + 1] = 255; // Green Value of current pixel  
                row[(x * 4) + 2] = 0; // Red value of current pixel  
            }  
        }  
    }  
}  

ATTENTION: Though the above might work (and let me stress might), it would probably be much more reliable to go to Bob Powell's site and read his page on LockBits. Though it may be hard to understand at first, it gets simpler as you go along. His page is much more detailed than I could be in this answer, and he probably has working examples.