point_of_sale_v2/PointOfSale/Utilities/ESCPOS_NET/Extensions/ImageSharpExtensions.cs

using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;

namespace SixLabors.ImageSharp
{
    public static class ImageSharpExtensions
    {
        public static byte[] ToSingleBitPixelByteArray(this Image<Rgba32> image, bool rasterFormat = true, int? maxWidth = null, int? maxHeight = null, float threshold = 0.5F)
        {
            image.Mutate(img =>
            {
                if (maxWidth.HasValue || maxHeight.HasValue)
                {
                    img.Resize(new ResizeOptions
                    {
                        Mode = ResizeMode.Max,
                        Size = new Size(maxWidth ?? int.MaxValue, maxHeight ?? int.MaxValue),
                    });
                }

                img.BackgroundColor(Color.White);
                img.Grayscale().BinaryDither(KnownDitherings.Stucki);

                if (!rasterFormat)
                {
                    img.Rotate(RotateMode.Rotate90);
                    img.Flip(FlipMode.Horizontal);
                }
            });

            var result = image.ToSingleBitPixelByteArray();
            return result;
        }

        private static byte[] ToSingleBitPixelByteArray(this Image<Rgba32> image)
        {
            var bytesPerRow = (image.Width + 7 & -8) / 8;

            var result = new byte[bytesPerRow * image.Height];
            for (int y = 0; y < image.Height; y++)
            {
                var row = image.GetPixelRowSpan(y);
                var rowStartPosition = y * bytesPerRow;

                for (int x = 0; x < row.Length; x++)
                {
                    if (!row[x].IsBlack())
                    {
                        continue;
                    }

                    result[rowStartPosition + (x / 8)] |= (byte)(0x01 << (7 - (x % 8)));
                }
            }

            return result;
        }

        private static bool IsBlack(this Rgba32 rgba)
        {
            return rgba.R == 0 && rgba.G == 0 && rgba.B == 0;
        }
    }
}