How can I convert a bitmap to a 2D array of integers and vice versa in C#?

private void forwardFftButton_Click(object sender, EventArgs e)
        {
            Bitmap grayscale = (Bitmap) GrayscaleUtils.ColorToGrayscale(inputImagePictureBox.Image);

            grayscaleImagePictureBox.Image = grayscale;

            int[,] array2D = ImageDataConverter.BitmapToArray2D(grayscale);

            Bitmap grayScaleAgain = ImageDataConverter.Array2DToBitmap(array2D);

            processedImagePictureBox.Image = grayScaleAgain;
        }

using System;
using System.Drawing;
using System.Drawing.Imaging;

public partial class ImageDataConverter
{
	public static int[, ] BitmapToArray2D(Bitmap image)
	{
		int[, ] array2D = null;
		if (image.PixelFormat == PixelFormat.Format8bppIndexed)
		{
			array2D = new int[image.Width, image.Height];
			BitmapData bitmapData = image.LockBits(new Rectangle(0, 0, image.Width, image.Height), ImageLockMode.ReadOnly, PixelFormat.Format8bppIndexed);
			int paddingOffset = bitmapData.Stride - (bitmapData.Width * 1); //1 == 1-byte per pixel
			unsafe
			{
				byte *memoryAddress = (byte *)bitmapData.Scan0;
				for (int i = 0; i < bitmapData.Width; i++)
				{
					for (int j = 0; j < bitmapData.Height; j++)
					{
						byte tempByte = memoryAddress[0];
						array2D[i, j] = (int)tempByte;
						int tempArrayElement = array2D[i, j];
						//1-byte per pixel
						memoryAddress += 1;
					}

					memoryAddress += paddingOffset;
				}
			}

			image.UnlockBits(bitmapData);
		}
		else
		{
			throw new Exception("8 bit/pixel indexed image required.");
		}

		return array2D;
	}

	public static Bitmap Array2DToBitmap(int[, ] image)
	{
		Bitmap output = new Bitmap(image.GetLength(0), image.GetLength(1));
		BitmapData bitmapData = output.LockBits(new Rectangle(0, 0, image.GetLength(0), image.GetLength(1)), ImageLockMode.ReadOnly, PixelFormat.Format32bppArgb);
		int paddingOffset = bitmapData.Stride - (bitmapData.Width * 1); //1 == 1-byte per pixel
		unsafe
		{
			byte *memoryAddress = (byte *)bitmapData.Scan0;
			for (int i = 0; i < bitmapData.Height; i++)
			{
				for (int j = 0; j < bitmapData.Width; j++)
				{
					int tempInt = image[j, i];
					memoryAddress[0] = (byte)tempInt;
					byte tempByte = memoryAddress[0];
					//1-byte per pixel
					memoryAddress += 1;
				}

				memoryAddress += paddingOffset;
			}
		}

		output.UnlockBits(bitmapData);
		return output;
	}
}