update test that generates readme header spectrogram

Author: swharden

README.md

@@ -3,11 +3,11 @@
 [![](https://img.shields.io/azure-devops/build/swharden/swharden/9?label=Build&logo=azure%20pipelines)](https://dev.azure.com/swharden/swharden/_build/latest?definitionId=9&branchName=master)
 [![Nuget](https://img.shields.io/nuget/v/Spectrogram?label=NuGet&logo=nuget)](https://www.nuget.org/packages/Spectrogram/)
 
-**Spectrogram** is a .NET library for creating spectrograms from pre-recorded signals or live audio from the sound card.  Spectrogram uses FFT algorithms and window functions provided by the [FftSharp](https://github.com/swharden/FftSharp) project, and it targets .NET Standard 2.0 so it can be used in .NET Framework and .NET Core projects.
+**Spectrogram** is a .NET library for creating spectrograms from pre-recorded signals or live audio from the sound card.  Spectrogram uses FFT algorithms and window functions provided by the [FftSharp](https://github.com/swharden/FftSharp) project, and it targets .NET Standard so it can be used in .NET Framework and .NET Core projects.
 
 <div align="center">
 
-![](dev/spectrogram.png)
+![](dev/graphics/hal-spectrogram.png)
 
 _"I'm sorry Dave... I'm afraid I can't do that"_
 

dev/graphics/hal-spectrogram.png

@@ -33,6 +33,18 @@ public void Test_Quickstart_Hal()
             Console.WriteLine(spec);
         }
 
+        [Test]
+        public void Test_Readme_HeaderImage()
+        {
+            (double[] audio, int sampleRate) = TestTools.ReadWavWithNAudio("../../../../../data/cant-do-that-44100.wav");
+            int fftSize = 2048;
+            var spec = new Spectrogram(sampleRate, fftSize, stepSize: 400, maxFreq: 6000);
+            spec.Add(audio);
+            spec.SaveImage("../../../../../dev/graphics/hal-spectrogram.png", intensity: 10, dB: true, dBScale: 500);
+
+            Console.WriteLine(spec);
+        }
+
         [Test]
         public void Test_Quickstart_Handel()
         {

src/Spectrogram.Tests/Quickstart.cs

@@ -10,7 +10,14 @@ namespace Spectrogram
 {
     public static class Image
     {
-        public static Bitmap GetBitmap(List<double[]> ffts, Colormap cmap, double intensity = 1, bool dB = false, 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)
         {
             if (ffts.Count == 0)
                 throw new ArgumentException("This Spectrogram contains no FFTs (likely because no signal was added)");
@@ -40,7 +47,7 @@ public static Bitmap GetBitmap(List<double[]> ffts, Colormap cmap, double intens
                 {
                     double value = ffts[sourceCol][row];
                     if (dB)
-                        value = 20 * Math.Log10(value + 1);
+                        value = 20 * Math.Log10(value * dBScale + 1);
                     value *= intensity;
                     value = Math.Min(value, 255);
                     int bytePosition = (Height - 1 - row) * stride + col;

src/Spectrogram/Image.cs

@@ -136,22 +136,22 @@ public List<double[]> GetMelFFTs(int melBinCount)
                 throw new InvalidOperationException("cannot get Mel spectrogram unless minimum frequency is 0Hz");
 
             var fftsMel = new List<double[]>();
-            foreach(var fft in ffts)
+            foreach (var fft in ffts)
                 fftsMel.Add(FftSharp.Transform.MelScale(fft, SampleRate, melBinCount));
 
             return fftsMel;
         }
 
-        public Bitmap GetBitmap(double intensity = 1, bool dB = false, bool roll = false) =>
-            Image.GetBitmap(ffts, cmap, intensity, dB, roll, NextColumnIndex);
+        public Bitmap GetBitmap(double intensity = 1, bool dB = false, double dBScale = 1, bool roll = false) =>
+            Image.GetBitmap(ffts, cmap, intensity, dB, dBScale, roll, NextColumnIndex);
 
-        public Bitmap GetBitmapMel(int melBinCount = 25, double intensity = 1, bool dB = false, bool roll = false) =>
-            Image.GetBitmap(GetMelFFTs(melBinCount), cmap, intensity, dB, roll, NextColumnIndex);
+        public Bitmap GetBitmapMel(int melBinCount = 25, double intensity = 1, bool dB = false, double dBScale = 1, bool roll = false) =>
+            Image.GetBitmap(GetMelFFTs(melBinCount), cmap, intensity, dB, dBScale, roll, NextColumnIndex);
 
         [Obsolete("use SaveImage()", true)]
         public void SaveBitmap(Bitmap bmp, string fileName) { }
 
-        public void SaveImage(string fileName, double intensity = 1, bool dB = false, bool roll = false)
+        public void SaveImage(string fileName, double intensity = 1, bool dB = false, double dBScale = 1, bool roll = false)
         {
             if (ffts.Count == 0)
                 throw new InvalidOperationException("Spectrogram contains no data. Use Add() to add signal data.");
@@ -170,10 +170,10 @@ public void SaveImage(string fileName, double intensity = 1, bool dB = false, bo
             else
                 throw new ArgumentException("unknown file extension");
 
-            Image.GetBitmap(ffts, cmap, intensity, dB, roll, NextColumnIndex).Save(fileName, fmt);
+            Image.GetBitmap(ffts, cmap, intensity, dB, dBScale, roll, NextColumnIndex).Save(fileName, fmt);
         }
 
-        public Bitmap GetBitmapMax(double intensity = 1, bool dB = false, bool roll = false, int reduction = 4)
+        public Bitmap GetBitmapMax(double intensity = 1, bool dB = false, double dBScale = 1, bool roll = false, int reduction = 4)
         {
             List<double[]> ffts2 = new List<double[]>();
             for (int i = 0; i < ffts.Count; i++)
@@ -185,7 +185,7 @@ public Bitmap GetBitmapMax(double intensity = 1, bool dB = false, bool roll = fa
                         d2[j] = Math.Max(d2[j], d1[j * reduction + k]);
                 ffts2.Add(d2);
             }
-            return Image.GetBitmap(ffts2, cmap, intensity, dB, roll, NextColumnIndex);
+            return Image.GetBitmap(ffts2, cmap, intensity, dB, dBScale, roll, NextColumnIndex);
         }
 
         public void SaveData(string filePath, int melBinCount = 0)