C#でBitmapオブジェクトとbyte配列を変換する。

using System.Drawing.Imaging;

namespace BitmapToBytes;

public partial class Form1 : Form
{
    // Bitmapオブジェクトをbyte配列に変換
    static public byte[] BitmapToBytes(Bitmap src)
    {
        var bmpData = src.LockBits(
            new Rectangle(0, 0, src.Width, src.Height),
            ImageLockMode.ReadOnly,
            src.PixelFormat);
        
        byte[] bytes = new byte[Math.Abs(bmpData.Stride) * src.Height];

        System.Runtime.InteropServices.Marshal.Copy(
            bmpData.Scan0,
            bytes, 0, bytes.Length);
        
        src.UnlockBits(bmpData);

        return bytes;
    }
    // byte配列をにBitmapオブジェクト変換
    static public Bitmap BytesToBitmap(byte[] bytes, int width, int height, PixelFormat format)
    {
        var dst = new Bitmap(width, height, format);

        var bmpData = dst.LockBits(
            new Rectangle(0, 0, dst.Width, dst.Height),
            ImageLockMode.ReadWrite,
            dst.PixelFormat);

        System.Runtime.InteropServices.Marshal.Copy(
            bytes,
            0, bmpData.Scan0,
            bytes.Length);
        dst.UnlockBits(bmpData);

        return dst;
    }
    public Form1()
    {
        InitializeComponent();

        var bmp = new Bitmap(@"H:\202211181317.PNG");

        byte[] bytes = BitmapToBytes(bmp);

        int channel = Bitmap.GetPixelFormatSize(bmp.PixelFormat) / 8;
        int stride = bytes.Length / bmp.Height;
        // int stride = (bmp.Width * (8 * channel) + 31) / 32 * 4;

        // 平均値フィルタ 3x3
        double[,] kernel = new double[,] {
            {1.0/9.0, 1.0/9.0, 1.0/9.0,},
            {1.0/9.0, 1.0/9.0, 1.0/9.0,},
            {1.0/9.0, 1.0/9.0, 1.0/9.0,},
        };
        for (int c = 0; c < channel; c++)
        {
            for (int y = 1; y < (bmp.Height-1); y++)
            {
                for (int x = 1; x < (bmp.Width-1); x++)
                {
                    double avg = 0.0;
                    avg += bytes[(y-1) * stride + (x-1) * channel + c] * kernel[0,0];
                    avg += bytes[(y-1) * stride + (x+0) * channel + c] * kernel[0,1];
                    avg += bytes[(y-1) * stride + (x+1) * channel + c] * kernel[0,2];
                    avg += bytes[(y+0) * stride + (x-1) * channel + c] * kernel[1,0];
                    avg += bytes[(y+0) * stride + (x+0) * channel + c] * kernel[1,1];
                    avg += bytes[(y+0) * stride + (x+1) * channel + c] * kernel[1,2];
                    avg += bytes[(y+1) * stride + (x-1) * channel + c] * kernel[2,0];
                    avg += bytes[(y+1) * stride + (x+0) * channel + c] * kernel[2,1];
                    avg += bytes[(y+1) * stride + (x+1) * channel + c] * kernel[2,2];
                    bytes[y * stride + x * channel + c] = (byte)avg;
                }
            }
        }

        Bitmap bmp2 = BytesToBitmap(bytes, bmp.Width, bmp.Height, bmp.PixelFormat);

        PictureBox picbox = new()
        {
            SizeMode = PictureBoxSizeMode.AutoSize,
            Image = bmp2,
        };
        Panel panel = new()
        {
            AutoScroll = true,
            Dock = DockStyle.Fill,
        };
        panel.Controls.Add(picbox);
        Controls.Add(panel);
    }
}