How to get pixel color from richtextbox

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on richTextBox(bachground color black and white forground) i wrote letter y
from the richTextBox i want to get the color of the rectangle size 64X64 pixels.
the problem as you may gussed i could not get a bitmap from the richTextBox
see line A

What I have tried:

C#

Color[,] pixelColor = new Color[100, 100];
//objMyBitMap = new Bitmap(640, //480,System.Drawing.Imaging.PixelFormat.Format24bppRgb);

            Bitmap rtb = (Bitmap)richTextBox1.Clone();//<-------  Line A
            for (i = 1; i < 64+1; i++)
            {
                for (j = 1; j < 64+1; j++)
                {
                    //pixelColor[i,j] = objMyBitMap.GetPixel(i, j);
                    pixelColor[i,j] = rtb.GetPixel(i, j);
                }
            }

Posted 5-Feb-16 18:07pm

Engineer khalid

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Sergey Alexandrovich Kryukov 6-Feb-16 1:09am

I wonder why? the idea is correct, except the first line...
Is it System.Windows.Forms.RichTextBox? Always indicate at least one full type name in such questions...
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2016-02-05T19:30:00

You cannot cast a control into Bitmap. You have to do different thing: copy a part of the screen from the bounding rectangle of the control. Most likely, you are using System.Windows.Forms and System.Drawing. If so, you can use System.Drawing.Graphics.CopyFromScreen:
Graphics.CopyFromScreen Method (Int32, Int32, Int32, Int32, Size) (System.Drawing)[^].

To copy part of the screen into a bitmap, first create a bitmap instance of required size and obtain an instance of System.Drawing.Graphics which can be used to draw in this bitmap: Graphics.FromImage Method (Image) (System.Drawing)[^].

Another problem is: GetPixel is prohibitively slow. Instead, you have to use one of the methods System.Drawing.Bitmap.LockBits:
Bitmap.LockBits Method (Rectangle, ImageLockMode, PixelFormat) (System.Drawing)[^].

Few words on the expected result: it's pretty obvious that RTF document, in a way, does not have its own pixel colors. Its rendering depends on the device, current layout of the bounding rectangle, system settings and other detail. If, say, you use just black text of white background, you will get several colors used for, in particular, anti-aliasing and ClearType effect. It makes me feel puzzled about the purpose of your question.

—SA