Spectrogram Orientation

[padesso]

Hi Scott,

I've been working with your Spectrogram for a few weeks and like it very much. I was able to integrate into my project but am considering updating it to support both the existing horizontal orientation as well as vertical. It's not a trivial change and I also don't think I can accomplish it without breaking changes. Do you have any plans to do so? Would it be an appealing PR?

[swharden]

Hi @padesso I'm happy to hear you're enjoying Spectrogram!

Adding a top-down orientation is a good idea. "Waterfall" displays are really common (especially in RF analysis) so supporting this makes sense. Probably the simplest way to do this is to add a bool horizontal = true argument to the Spectrogram.GetBitmap method:

Spectrogram/src/Spectrogram/Spectrogram.cs

Lines 145 to 146 in 555e1cc

	public Bitmap GetBitmap(double intensity = 1, bool dB = false, bool roll = false) =>
	Image.GetBitmap(ffts, cmap, intensity, dB, roll, NextColumnIndex);

...then add that same argument to the Image.GetBitmap method. You'd have to refactor this method a bit to support vertical orientation, but support could be added just by refactoring this method:

Spectrogram/src/Spectrogram/Image.cs

Lines 13 to 56 in 555e1cc

	public static Bitmap GetBitmap(List<double[]> ffts, Colormap cmap, double intensity = 1, bool dB = false, bool roll = false, int rollOffset = 0)
	{
	if (ffts.Count == 0)
	throw new ArgumentException("This Spectrogram contains no FFTs (likely because no signal was added)");
	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 =>
	{
	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 + 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;
	}
	}

If you want to have a go at adding this feature you're welcome to make a PR! If you don't get around to it, I'll leave this issue open and try to support this feature some time in the future. Thanks for the suggestion!

[swharden]

... and perhaps a bool reverse = false argument would be helpful too? This could simply reverse the FFTs prior to plotting them, but the argument could control whether the waterfall display scrolls upward or downward 🤔

[padesso]

Thanks for the quick response! I think that by far the most common use case, and coincidentally mine for a radio project :) using this would be waterfall and particularly done in a way so it could be aligned with a graphical equalizer that shows peaks of the audio Your suggestion is certainly where I will start to look at this. There are some other more minor areas (like the scale bar) that will need to be touched but I aim to start looking into the implementation details in the evenings this week and will stay in touch on this issue with progres/blockers.

[swharden]

Sounds great! I'll keep an eye out for a PR, but let me know if you have any questions along the way.

You may find helpful code at https://github.com/swharden/FSKview such as Ruler.cs

[padesso]

Just checking in with you. I have the spectrogram in a waterfall orientation but need to complete some work on the scale bar and do some validation. I haven't been able to focus on it because of work but expect to pick this back up soon.

[swharden]

Just checking in with you. I have the spectrogram in a waterfall orientation but need to complete some work on the scale bar and do some validation. I haven't been able to focus on it because of work but expect to pick this back up soon.

Hey, no worries! I appreciate you working on it, and definitely take as long as you need to do it well 👍

I'm happy to leave this issue open a while longer so it stays on both of our radars. I'm happy to see what you come up with!

Best,
Scott

[swharden]

I haven't seen movement on this for a while so I'll close this issue, but if/when the topic arises again I'll open this back up and pick up where we left off 👍