How to make a checkerboard pattern for a transparent picture background in C#?

Question

2D

I am writing a thumbnail generator for graphic files (including transparent gif and png). The output is jpeg. If the source file had transparent areas, then black is displayed instead of them by default. It can be filled with a different color or pattern or texture. Everything is clear here:

public static Image Resize(this Image image,
  int maxWidth, int maxHeight, bool notIncrease = true)
{
  int w = image.Width;
  int h = image.Height;
  if (notIncrease && (w <= maxWidth && h <= maxHeight))
    return (Image)image.Clone();
  float ratioX = (float)maxWidth / (float)w;
  float ratioY = (float)maxHeight / (float)h;
  float ratio = Math.Min(ratioX, ratioY);
  int newWidth = (int)(w * ratio);
  int newHeight = (int)(h * ratio);
  Image res = new Bitmap(newWidth, newHeight,
    PixelFormat.Format24bppRgb);
  using (var g = Graphics.FromImage(res))
  {
    g.FillRectangle(Brushes.Gray, 0, 0, newWidth, newHeight);
    g.CompositingQuality =
      CompositingQuality.HighQuality;
    g.InterpolationMode =
      InterpolationMode.HighQualityBicubic;
    g.SmoothingMode =
      SmoothingMode.HighQuality;
    g.DrawImage(image, 0, 0,
      newWidth, newHeight);
  }
  return res;
}

I would like to make everything beautiful and display a transparent background not in gray, but in the form of a "checkerboard", as, for example, in Photoshop. To do this, as I understand it, you can substitute a TextureBrush that will contain the desired ornament.
The question is how to create this TextureBrush so that this operation takes a minimum of machine time. Ideally, get the brush from a constant byte array. How can this be done?
An example of the code "on the forehead" for generating a brush for a checkerboard fill:

var bitmap = new Bitmap(20, 20);
using (var gg = Graphics.FromImage(bitmap))
{
  gg.FillRectangle(Brushes.Gray, 0, 0, 10, 10);
  gg.FillRectangle(Brushes.LightGray, 10, 0, 10, 10);
  gg.FillRectangle(Brushes.LightGray, 0, 10, 10, 10);
  gg.FillRectangle(Brushes.Gray, 10, 10, 10, 10);
}
var brush = new TextureBrush(bitmap);

You need something like this:

var bitmap = new Bitmap(20, 20) = {
  0x99,0x99,0x99,	0xcc,0xcc,0xcc,
  0x99,0x99,0x99,	0xcc,0xcc,0xcc,
  0x99,0x99,0x99,	0xcc,0xcc,0xcc,

  0xcc,0xcc,0xcc,	0x99,0x99,0x99,
  0xcc,0xcc,0xcc,	0x99,0x99,0x99,
  0xcc,0xcc,0xcc,	0x99,0x99,0x99,
};			
var brush = new TextureBrush(bitmap);

Answer 1

because we are talking about performance, then I would immediately prefer filling manually, without using brushes. so to speak, "to avoid misunderstandings." that is, 2 LockBits and a manual line-by-line copy (no need to BLIT or DrawImage) in a loop. well, yes, and the picture for filling over there is created for you above =) it’s quite static for itself)

Answer 2

I guessed about LockBits, but I don’t know how to do it ...