how to calculate data for more files..in a single attempt..

As I said in my last comment to your prior question, I don't think you should be creating files to be used in Excel. I think you should load the two images into two Bitmap variables and do your comparison within the program.

That said, below is a sample program that does what you requested.

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1. Selects .JPG files from the directory in textBox1.Text
    Example: C:\\Users\\Mike\\Pictures\\Family
2. Uses original filename with .CSV replacing .JPG
3. Displays WaitCursor during operation
4. Counts files created and displays result when done
5. Uses Application.DoEvents() to allow other Windows processes to run occasionally

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Diagnostics;
using System.IO;


namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            int fileCount = 0;
            Cursor.Current = Cursors.WaitCursor;
            IEnumerable<string> files = Directory.EnumerateFiles(textBox1.Text);  // textBox1.Text contains a directory name
            foreach (var sourceFilename in files)
            {
                // Construct new filename substituting .CSV for the file extension
                string newFilename = System.IO.Path.GetDirectoryName(sourceFilename) + "\\" + System.IO.Path.GetFileNameWithoutExtension(sourceFilename) + ".CSV"; // Use filename and append .CSV extension
                string fileExtension = System.IO.Path.GetExtension(sourceFilename).ToLower(); // Get the original file extension
                if (fileExtension == ".jpg")  // Select only jpg files 
                {
                    using (FileStream fs = File.Create(newFilename)) // Create the new CSV file
                    {
                        using (TextWriter w = new StreamWriter(fs))
                        {
                            int i;
                            int j;
                            Bitmap bm = new Bitmap(sourceFilename);
                            for (i = 0; i < bm.Width; i++)
                            {
                                Application.DoEvents();  // Let other Windows processes run
                                for (j = 0; j < bm.Height; j++)
                                {
                                    Application.DoEvents();  // Let other Windows processes run
                                    Color pixelColor = bm.GetPixel(i, j);
                                    w.Write(pixelColor.R + "," + pixelColor.G + "," + pixelColor.B + "\r\n");
                                }
                            }
                            w.Close(); // Close the CSV file
                            fileCount++;
                        }

                    }
                }
                Application.DoEvents(); // Let other Windows processes run
            }
            Cursor.Current = Cursors.Default;
            MessageBox.Show(String.Format("{0} files processed.", fileCount));
        }

    }
}