Samsung test task - Simple vinyl reader in C#

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Imaging;
using NAudio.Wave;

namespace Funbit.VinylDecoder
{
    class Program
    {
        static byte[,] ReadGrayscaleVinylBitmapData(string imageFileName)
        {
            using (var image = Image.FromFile(imageFileName))
            using (var bitmap = new Bitmap(image))
            {
                var bitmapData = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height),
                                                 ImageLockMode.ReadWrite, bitmap.PixelFormat);
                IntPtr ptr = bitmapData.Scan0;
                int totalBytes = bitmapData.Stride * bitmap.Height;
                byte[,] grayValues = new byte[bitmap.Width, bitmap.Height];
                byte[] rgbValues = new byte[totalBytes];
                System.Runtime.InteropServices.Marshal.Copy(ptr, rgbValues, 0, totalBytes);
                bitmap.UnlockBits(bitmapData);
                int channels = bitmapData.Stride / bitmap.Width;
                for (int y = 0; y < bitmapData.Height; y++)
                {
                    for (int x = 0; x < bitmapData.Width; x++)
                    {
                        // since image is in grayscale RGB we can use any channel (1st is ok)
                        grayValues[x, y] = rgbValues[y * bitmapData.Stride + x * channels];
                    }
                }
                return grayValues;
            }
        }

        static void ProcessVinylImage(string imageFileName, Point outerStartPoint,
            int roads, int vinylInnerRadius, int vinylOuterRadius, string outputWaveFileName)
        {
            var imageData = ReadGrayscaleVinylBitmapData(imageFileName);
            using (var logImage = Image.FromFile(imageFileName))
            using (var logBitmap = new Bitmap(logImage))
            {
                const int sampleBaselineShift = 70 / 4; // 70 - grayscale value
                const int rpm = 120;

                int rate = (int)(2 * Math.PI * vinylOuterRadius * (rpm / 60));
                int centerX = outerStartPoint.X;
                int centerY = outerStartPoint.Y + vinylOuterRadius;
                List<byte> waveData = new List<byte>(roads * rate);
                double r = vinylOuterRadius,
                    phi = 0,
                    dr = ((double)vinylOuterRadius - vinylInnerRadius) / roads;

                do
                {
                    double x = Math.Cos((-Math.PI / 2) - phi) * r + centerX;
                    double y = Math.Sin((-Math.PI / 2) - phi) * r + centerY;

                    logBitmap.SetPixel((int)x, (int)y, Color.Red);

                    byte sample = (byte)(imageData[(int)x, (int)y] - sampleBaselineShift);
                    waveData.Add(sample);
                    phi += 1.0d / vinylOuterRadius;
                    r = vinylOuterRadius - ((phi / (Math.PI * 2)) * dr);
                } while (r > vinylInnerRadius);

                WaveFormat format = new WaveFormat(rate, 8, 1);
                using (var writer = new WaveFileWriter(outputWaveFileName, format))
                {
                    writer.Write(waveData.ToArray(), 0, waveData.Count);
                }

                logBitmap.Save("play-log.png");
            }
        }

        static void Main(string[] args)
        {
            Console.WriteLine("Processing...");

            ProcessVinylImage("../../../../04.png", // input vinyl image
                new Point(996, 72), // needle start position in px
                39,  // total numbers of roads
                472, // radius of inner road
                935, // radius of outer road
                "play.wav"); // output wave file

            Console.WriteLine("Done.");
        }
    }
}