Converts a sprite (16x16 pixels) into a RotMG-like sprite (with outline and shadow)

SpriteImageProcessor.cs

using System;
using System.Diagnostics;
using SkiaSharp;

namespace AGES.Utils.Runtime.SpriteImageProcessor
{
    public class SpriteImageProcessor
    {
        public SpriteImageProcessor()
        {
            // Load the image
            using var bitmap = SKBitmap.Decode("Resources/input.png");

            // Upscale the image
            var scaledBitmap = bitmap.Resize(new SKImageInfo(bitmap.Width * 4, bitmap.Height * 4), SKFilterQuality.None);

            // Create a new bitmap to add border
            var bitmapWithBorder = new SKBitmap(scaledBitmap.Width + 2, scaledBitmap.Height + 2);

            using var canvas = new SKCanvas(bitmapWithBorder);
            // Draw the image 8 times to create border
            var paint = new SKPaint();
            paint.Color = new SKColor(0, 0, 0);
            for (int dx = -1; dx <= 1; dx++)
            {
                for (int dy = -1; dy <= 1; dy++)
                {
                    if (dx != 0 || dy != 0)
                    {
                        canvas.DrawBitmap(scaledBitmap, dx + 1, dy + 1, paint);
                    }
                }
            }

            // Replace all non transparent pixels with black
            for (int x = 0; x < bitmapWithBorder.Width; x++)
            {
                for (int y = 0; y < bitmapWithBorder.Height; y++)
                {
                    var pixel = bitmapWithBorder.GetPixel(x, y);
                    if (pixel.Alpha != 0)
                    {
                        bitmapWithBorder.SetPixel(x, y, new SKColor(0, 0, 0));
                    }
                }
            }


            // Draw the main image over the top
            canvas.DrawBitmap(scaledBitmap, 1, 1, paint);

            // Create bitmap for shadow
            var shadowBitmap = new SKBitmap(bitmapWithBorder.Width, bitmapWithBorder.Height);

            // Create black paint
            var shadowPaint = new SKPaint
            {
                Color = new SKColor(0, 0, 0),
                ImageFilter = SKImageFilter.CreateDropShadow(0, 0, 3, 3, SKColors.Black)
            };

            using var shadowCanvas = new SKCanvas(shadowBitmap);
            // Draw shadow
            shadowCanvas.DrawBitmap(bitmapWithBorder, 0, 0, shadowPaint);

            // Draw the main bitmap over the top
            shadowCanvas.DrawBitmap(bitmapWithBorder, 0, 0, paint);

            // Save the image to disk
            using var image = SKImage.FromBitmap(shadowBitmap);
            using var data = image.Encode();
            System.IO.File.WriteAllBytes("output.png", data.ToArray());

            // Open image in explorer
            Process.Start("explorer", "/select,\"" + AppDomain.CurrentDomain.BaseDirectory + "output.png\"");
        }
    }
}