GetBitmap: add rotate argument

resolves #47

Author: swharden

src/Spectrogram.Tests/ImageTests.cs

@@ -0,0 +1,21 @@
+using NUnit.Framework;
+
+namespace Spectrogram.Tests;
+
+internal class ImageTests
+{
+    [Test]
+    public void Test_Image_Rotations()
+    {
+        string filePath = $"../../../../../data/cant-do-that-44100.wav";
+        (double[] audio, int sampleRate) = AudioFile.ReadWAV(filePath);
+        SpectrogramGenerator sg = new(sampleRate, 4096, 500, maxFreq: 3000);
+        sg.Add(audio);
+
+        System.Drawing.Bitmap bmp1 = sg.GetBitmap(rotate: false);
+        bmp1.Save("test-image-original.png");
+
+        System.Drawing.Bitmap bmp2 = sg.GetBitmap(rotate: true);
+        bmp2.Save("test-image-rotated.png");
+    }
+}

src/Spectrogram/Image.cs

@@ -10,55 +10,22 @@ namespace Spectrogram
 {
     public static class Image
     {
-        public static Bitmap GetBitmap(
-            List<double[]> ffts,
-            Colormap cmap,
-            double intensity = 1,
-            bool dB = false,
-            double dBScale = 1,
-            bool roll = false,
-            int rollOffset = 0)
+        public static Bitmap GetBitmap(List<double[]> ffts, Colormap cmap, double intensity = 1,
+            bool dB = false, double dBScale = 1, bool roll = false, int rollOffset = 0, bool rotate = false)
         {
-            if (ffts.Count == 0)
-                throw new ArgumentException("Not enough data in FFTs to generate an image yet.");
 
-            int Width = ffts.Count;
-            int Height = ffts[0].Length;
-
-            Bitmap bmp = new Bitmap(Width, Height, PixelFormat.Format8bppIndexed);
-            cmap.Apply(bmp);
-
-            var lockRect = new Rectangle(0, 0, Width, Height);
-            BitmapData bitmapData = bmp.LockBits(lockRect, ImageLockMode.ReadOnly, bmp.PixelFormat);
-            int stride = bitmapData.Stride;
-
-            byte[] bytes = new byte[bitmapData.Stride * bmp.Height];
-            Parallel.For(0, Width, col =>
+            ImageMaker maker = new()
             {
-                int sourceCol = col;
-                if (roll)
-                {
-                    sourceCol += Width - rollOffset % Width;
-                    if (sourceCol >= Width)
-                        sourceCol -= Width;
-                }
-
-                for (int row = 0; row < Height; row++)
-                {
-                    double value = ffts[sourceCol][row];
-                    if (dB)
-                        value = 20 * Math.Log10(value * dBScale + 1);
-                    value *= intensity;
-                    value = Math.Min(value, 255);
-                    int bytePosition = (Height - 1 - row) * stride + col;
-                    bytes[bytePosition] = (byte)value;
-                }
-            });
-
-            Marshal.Copy(bytes, 0, bitmapData.Scan0, bytes.Length);
-            bmp.UnlockBits(bitmapData);
-
-            return bmp;
+                Colormap = cmap,
+                Intensity = intensity,
+                IsDecibel = dB,
+                DecibelScaleFactor = dBScale,
+                IsRoll = roll,
+                RollOffset = rollOffset,
+                IsRotated = rotate,
+            };
+
+            return maker.GetBitmap(ffts);
         }
     }
 }

src/Spectrogram/ImageMaker.cs

@@ -0,0 +1,101 @@
+using System;
+using System.Collections.Generic;
+using System.Drawing;
+using System.Drawing.Imaging;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Spectrogram
+{
+    /// <summary>
+    /// This class converts a collection of FFTs to a colormapped spectrogram image
+    /// </summary>
+    public class ImageMaker
+    {
+        /// <summary>
+        /// Colormap used to translate intensity to pixel color
+        /// </summary>
+        public Colormap Colormap;
+
+        /// <summary>
+        /// Intensity is multiplied by this number before converting it to the pixel color according to the colormap
+        /// </summary>
+        public double Intensity = 1;
+
+        /// <summary>
+        /// If True, intensity will be log-scaled to represent Decibels
+        /// </summary>
+        public bool IsDecibel = false;
+
+        /// <summary>
+        /// If <see cref="IsDecibel"/> is enabled, intensity will be scaled by this value prior to log transformation
+        /// </summary>
+        public double DecibelScaleFactor = 1;
+
+        /// <summary>
+        /// If False, the spectrogram will proceed in time from left to right across the whole image.
+        /// If True, the image will be broken and the newest FFTs will appear on the left and oldest on the right.
+        /// </summary>
+        public bool IsRoll = false;
+
+        /// <summary>
+        /// If <see cref="IsRoll"/> is enabled, this value indicates the pixel position of the break point.
+        /// </summary>
+        public int RollOffset = 0;
+
+        /// <summary>
+        /// If True, the spectrogram will flow top-down (oldest to newest) rather than left-right.
+        /// </summary>
+        public bool IsRotated = false;
+
+        public ImageMaker()
+        {
+
+        }
+
+        public Bitmap GetBitmap(List<double[]> ffts)
+        {
+            if (ffts.Count == 0)
+                throw new ArgumentException("Not enough data in FFTs to generate an image yet.");
+
+            int Width = IsRotated ? ffts[0].Length : ffts.Count;
+            int Height = IsRotated ? ffts.Count : ffts[0].Length;
+
+            Bitmap bmp = new(Width, Height, PixelFormat.Format8bppIndexed);
+            Colormap.Apply(bmp);
+
+            Rectangle lockRect = new(0, 0, Width, Height);
+            BitmapData bitmapData = bmp.LockBits(lockRect, ImageLockMode.ReadOnly, bmp.PixelFormat);
+            int stride = bitmapData.Stride;
+
+            byte[] bytes = new byte[bitmapData.Stride * bmp.Height];
+            Parallel.For(0, Width, col =>
+            {
+                int sourceCol = col;
+                if (IsRoll)
+                {
+                    sourceCol += Width - RollOffset % Width;
+                    if (sourceCol >= Width)
+                        sourceCol -= Width;
+                }
+
+                for (int row = 0; row < Height; row++)
+                {
+                    double value = IsRotated ? ffts[row][sourceCol] : ffts[sourceCol][row];
+                    if (IsDecibel)
+                        value = 20 * Math.Log10(value * DecibelScaleFactor + 1);
+                    value *= Intensity;
+                    value = Math.Min(value, 255);
+                    int bytePosition = (Height - 1 - row) * stride + col;
+                    bytes[bytePosition] = (byte)value;
+                }
+            });
+
+            Marshal.Copy(bytes, 0, bitmapData.Scan0, bytes.Length);
+            bmp.UnlockBits(bitmapData);
+
+            return bmp;
+        }
+    }
+}

src/Spectrogram/Spectrogram.csproj

@@ -21,6 +21,7 @@
     <EmbedUntrackedSources>true</EmbedUntrackedSources>
     <Deterministic>true</Deterministic>
     <ContinuousIntegrationBuild>true</ContinuousIntegrationBuild>
+	<LangVersion>latest</LangVersion>
   </PropertyGroup>
 
   <ItemGroup>

src/Spectrogram/SpectrogramGenerator.cs

@@ -267,15 +267,16 @@ public List<double[]> GetMelFFTs(int melBinCount)
         /// <param name="dB">If true, output will be log-transformed.</param>
         /// <param name="dBScale">If dB scaling is in use, this multiplier will be applied before log transformation.</param>
         /// <param name="roll">Behavior of the spectrogram when it is full of data. 
+        /// <param name="rotate">If True, the image will be rotated so time flows from top to bottom (rather than left to right). 
         /// Roll (true) adds new columns on the left overwriting the oldest ones.
         /// Scroll (false) slides the whole image to the left and adds new columns to the right.</param>
-        public Bitmap GetBitmap(double intensity = 1, bool dB = false, double dBScale = 1, bool roll = false)
+        public Bitmap GetBitmap(double intensity = 1, bool dB = false, double dBScale = 1, bool roll = false, bool rotate = false)
         {
             if (FFTs.Count == 0)
                 throw new InvalidOperationException("Not enough data to create an image. " +
                     $"Ensure {nameof(Width)} is >0 before calling {nameof(GetBitmap)}().");
 
-            return Image.GetBitmap(FFTs, Colormap, intensity, dB, dBScale, roll, NextColumnIndex);
+            return Image.GetBitmap(FFTs, Colormap, intensity, dB, dBScale, roll, NextColumnIndex, rotate);
         }
 
         /// <summary>