c# - Set the pixels of image to the values stored in an array of integers

Question

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

            string fileContent = File.ReadAllText("D:\pixels.txt");

            string[] integerStrings = fileContent.Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);

            int[] integers = new int[integerStrings.Length];

            for (int n = 0; n < integerStrings.Length; n++)
            {
                integers[n] = int.Parse(integerStrings[n]);
            }

            Bitmap my = new Bitmap(512, 512);

            for (int i = 0; i < 512; i++)
                for (int j = 0; j < 512; j++)
                    my.SetPixel(i, j, Color.Blue);
            my.Save("D:\my.jpg");

        }
    }
}

Instead of setting all the pixels to Blue as I've done, I want to use the values from the array.

This is how I save the pixels to a text file! They are integers from 0 to 255. Now I'm trying to deal with greyscale images so I don't need the R, G and B separately, that's why it's (R+G+B)/3.

using (Bitmap bitmap = new Bitmap("D:\6.jpg"))
    {
        int width = 512;
        int height = 512;
        TextWriter tw = new StreamWriter("D:\pixels.txt");

        for (int i = 0; i < height; i++)
        {
            for (int j = 0; j < width; j++)
            {
                Color color = bitmap.GetPixel(j, i);
                tw.Write((color.R + color.G + color.B) / 3 + " ");
            }
            //tw.Write(" ");
        }
        tw.Close();
    }

Answer 1

Since you already have grayscale values with 1 byte per color it makes sense to use Format8bppIndexed for new image:

// Create 8 bit per pixel bitmap
var bitmap = new Bitmap(512, 512, PixelFormat.Format8bppIndexed);

// Set grayscale color palette
var colorPalette = bitmap.Palette;
var colorEntries = colorPalette.Entries;

for ( int i = 0; i < 256; i++ )
{
    colorEntries[i] = Color.FromArgb(i, i, i);
}

// Apply changes to color pallete
bitmap.Palette = colorPalette;

// Retrieve bitmap data for efficient writes
var bitmapData = bitmap.LockBits(Rectangle.FromLTRB(0, 0, 512, 512), ImageLockMode.WriteOnly, PixelFormat.Format8bppIndexed);

// Allocate array to store intermediate pixel data
byte[] colorData = new byte[bitmapData.Stride * bitmapData.Height]; // 1 byte per pixel since it is 8bppIndexed format

for (int i = 0; integers.Length; i++)
{
    int line = i / 512;
    int position = i % 512;

    colorData[line * bitmapData.Stride + position] = (byte)integers[i]; // color values from file
}

// Copy computed pixel data to BitmapData
Marshal.Copy(colorData, 0, bitmapData.Scan0, colorData.Length);

bitmap.UnlockBits(bitmapData);

bitmap.Save("D:\test.bmp");