How to mirror an image horizontally?

I am a high school student. I want to mirror an image horizontally. I have figured out the method to mirror it vertically but I have no idea how to start this task.

I copy and pasted the code from the previous method and was looking for something to edit but have had no luck so far.

public void mirrorHorizontal()
  {
      Pixel[][] pixels = this.getPixels2D();
      Pixel leftPixel = null;
      Pixel rightPixel = null;
      int width = pixels[0].length;
      for (int row = 0; row < pixels.length; row++)
      {
         for (int col = 0; col < width / 2; col++)
         {
            leftPixel = pixels[row][col];
            rightPixel = pixels[row][width - 1 - col];
            leftPixel.setColor(rightPixel.getColor());
         }
      }
  }

How can I change this code to mirror the image horizontally?