Extract RGB channels value and display it

Question

1.80/5 (2 votes)

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VS2012

Hello, I want to get only RGB values from an image present in picture box and show it on my form. Code I have tried gives the whole pixel values( and also takes too much time to calculate pixels ) but I need to show only RGB values. Please help. Thanks in advance.
I am working on Image Processing and using C#.Net, VS 2012. I am not using EMGU CV.

What I have tried:

public void PixelValues()
        {
            newBitmap = (Bitmap)pictureBox1.Image;
            Bitmap pix = (Bitmap)newBitmap.Clone();
            for (int i = 0; i < pix.Width; i++)
            {
                for (int j = 0; j < pix.Height; j++)
                {
                    Color pixel = newBitmap.GetPixel(i, j);
                    int a = pixel.A;//Alpha
                    int r = pixel.R;
                    int g = pixel.G;
                    int b = pixel.B;

                    listBox1.Items.Add("Red: " + r.ToString() + " - " + "Green: " + g.ToString() + " - " + "Blue: " + b.ToString());
                }
            }
        }

Posted 23-Oct-17 20:14pm

Member 13341679

Updated 1-Nov-17 1:11am

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3 solutions

Solution 1

You seem to have two issues 1) function, 2) speed.

1) Edit your question: Does your code already do what you want, only too slow?
If not, what did your code do differently than you wanted it to?

2 a) Wrap your textbox access code in

C#

listBox1.SuspendLayout();
listBox1.Items.AddAllTheInterestingStuff();
listBox1.ResumeLayout();

It saves a lot of time that is otherwise wasted on redrawing the listbox for every single entry.

2 b) Have a look at Fast Pointerless Image Processing in .NET. It shows a way of speeding up access to image data.

Posted 24-Oct-17 0:07am

lukeer

Solution 2

In addition to Solution 1, I would like to draw your attention on a few issues:

1. You don't need the pix variable, or at least not in the piece of code you have shown. Removing the copy could spare a few cycles (but that won't be a drastic improvement either).

2. You don't need the a variable, since you are not interested in the alpha value. Removing it will spare a fair amount of cycles since its assignation is done inside your nested for loops. r, g and b variables are not really mandatory either, unless for debuging purposes; but if you do not want to use them elsewhere than in the string building, you can get rid of them too.

3. String concatenations, especially in long loops, are also quite time consuming since they involve a lot of string copy operations internally. Here I would use a StringBuilder to try to gain some performance.
This way:

C#

using System.Text;

public void PixelValues()
{
   listBox1.SuspendLayout(); // Thanks to lukeer
   newBitmap = (Bitmap)pictureBox1.Image;
   Color pixel;
   StringBuilder sb = new StringBuilder(33); // 33 = max length of the string when all values are three digits long (quick count - could be wrong)
   for (int i = 0; i < pix.Width; i++)
   {
      for (int j = 0; j < pix.Height; j++)
      {
         pixel = newBitmap.GetPixel(i, j);
         sb.AppendFormat("Red: {0} - Green: {1} - Blue: {2}", pixel.R, pixel.G, pixel.B);
         listBox1.Items.Add(sb.ToString());
         sb.Clear();
      }
   }
   listBox1.ResumeLayout(); // Thanks to lukeer
}

You could also use a List<string> instead of adding items to the ListBox one by one, and add the whole lot of them at the end with the AddRange method of the ListBox class, but I'm not sure it would give a significant improvement. That could be tested, though, just to be sure.

Hope this helps. Kindly.

Posted 24-Oct-17 16:47pm

phil.o

Comments

Member 13341679 25-Oct-17 3:02am

@phil.o No changes in output, same as before.

phil.o 25-Oct-17 5:02am

Just out ouf curiosity, what are the width and height of the picture?

Member 13341679 25-Oct-17 5:11am

It's dynamic. One can take any kind of pictures. It's a UI.

phil.o 25-Oct-17 5:15am

I get it. But what for the image you are using during your test?

Member 13341679 25-Oct-17 5:17am

Image processing, applying different filters to enhance the picture clarity.

phil.o 25-Oct-17 6:09am

Sorry, this is not my question. What is the size of the actual image you are using during your test, specifically?

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Member 13341679 · Accepted Answer · 2017-11-01T01:11:00

I found the solution and here is the code. It's giving the exact output I wanted.

private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (opened)
                {
                    newBitmap = (Bitmap)pictureBox1.Image;

                    label1.Text = "X= " + e.X + " ; Y= " + e.Y;//Gives mouse pointer coordinate on the image
                    Color color = newBitmap.GetPixel(e.Location.X, e.Location.Y);
                    label2.Text = string.Format("RGB Values:  {0}, {1}, {2}", color.R, color.G, color.B);//Returns pixel value at mouse position   
                }
        }