How to get the RGB values of each pixel in the windows form with GDI+ ?

Question

Hi all I'm new to GDI+ and C# Recently I try to implement a painer I want to get each pixel's RGB values in the form when I click the mouse. In the MouseDown function I have tried this.GetChildAtPoint(pt).ForeColor.ToArgb(); but Exception Error!! comes up. How should I solve this problem? Thanks... :)

im547.cis93g · Answer

I find a alternative way to achieve my purpose: 1. Create a bitmap Bitmap myBitMap; 2. In OnPaint function use this.BackgroundImage = myBitMap; to load bg-image for the form now we can access the pixels from the Bitmap and the status would display in the form. :)

im547.cis93g · Answer

if I put this.GetChildAtPoint(pt).ForeColor; into OnPaint function protected override void OnPaint(PaintEventArgs e) { Graphics g = e.Graphics ; g.FillRectangle(new SolidBrush(Color.White) ClientRectangle); Pen pn = new Pen( Color.FromArgb(616161) 2 ); for(int i=0;i<pointArray.Count;i++){ Point pt = (Point) pointArray[i]; Color tmp = this.GetChildAtPoint(pt).ForeColor; g.DrawEllipse( pn pt.X pt.Y 4 4); } this.Invalidate(); } =========================================================== or put it into MouseDown function: private void Form1_MouseDown(object sender System.Windows.Forms.MouseEventArgs e) { Point pt = new Point(e.Xe.Y); if (this.GetChildAtPoint(pt).ForeColor.IsEmpty==false) { this.GetChildAtPoint(pt).ForeColor.ToArgb(); } } =========================================================== In these circumstances when I try to paint some point on the Form it would result in System.NullReferenceException the error msgs are as below: =========================================================== System.NullReferenceException: at painter.Form1.OnPaint(PaintEventArgs e) in c:\documents and settings\ovaltine1015\??\painter\painter\form1.cs:line 71 at System.Windows.Forms.Control.PaintWithErrorHandling(PaintEventArgs e Int16 layer Boolean disposeEventArgs) at System.Windows.Forms.Control.WmPaint(Message& m) at System.Windows.Forms.Control.WndProc(Message& m) at System.Windows.Forms.ScrollableControl.WndProc(Message& m) at System.Windows.Forms.ContainerControl.WndProc(Message& m) at System.Windows.Forms.Form.WndProc(Message& m) at System.Windows.Forms.ControlNativeWindow.OnMessage(Message& m) at System.Windows.Forms.ControlNativeWindow.WndProc(Message& m) at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd Int32 msg IntPtr wparam IntPtr lparam) ============================================================ Thank you for your advising. :)

jimteeuwen · Answer

What exactly is the Exception it generates?

dj_toffo · Answer

Hi new to this forum as well basically want the same thing to read the color of the pixel at the mouse position in a picturebox. Im trying to do A clickable map of Europe wish seems like a simple thing but I want it to recognize the land by color so.