.NET images read from memory and Convert Commands

[EricBatlle]

Hi @dlemstra , first of all, many thanks for your AWESOME library and your continuous maintenance!

Now going to my question, I want to do some convert -auto-gamma and -normalize commands on to a bunch of images but doing it by CMD with something like:

$"magick convert *.png -normalize {path}" takes too long (nearly 5 seconds for 60 grayscale frames of 256x520 ) and I'm starting to think that this is caused to handling static images instead of memory-ones.

So my questions are:

1. How can I work with memory images (byte[]) instead of static ones? I expected that this library with the new ImageMagcik(byte[]) can do that, but I'm stuck trying to find how to apply convert to those virtual images...
2. There is a way with Magick.NET to achieve that?
3. Why takes so long to perform a -normalize filter?

In case it helps, I've tried to do my own normalize filter before reaching you, it's fast (really fast) but the results aren't the same as yours...
4.Why?

public class NormalizeFilter
{
	private static double maxGlobalPixelValue = 255;
	private static double minGlobalPixelValue = 0;
	private static double minThresholdPercentage = 0.02;
	private static double maxThresholdPercentage = 0.99;

	private double maxLocalPixelValue = 0;
	private double minLocalPixelValue = 255;

	private double normalizationFactor = 0;

	//Create filter using as normalization factor the frame passed
	public NormalizeFilter(byte[] framePixelsToCalculateNormalizationFactor, bool useThresholds = true)
	{
		normalizationFactor = useThresholds ? GetNormalizationFactor(framePixelsToCalculateNormalizationFactor) : GetNormalizationFactorWithoutThreshold(framePixelsToCalculateNormalizationFactor);
	}

	//Aply Normalize filter with normalizationFactor previously calculated
	public byte[] ApplyTo(byte[] framePixels)
	{
		byte[] framePixelsNormalizeds = new byte[framePixels.Length];

		double pixelUnnormalizedValue = 0;
		double pixelNormalizedValue = 0;
		for (int i = 0; i < framePixels.Length; i++)
		{
			pixelUnnormalizedValue = framePixels[i];
			pixelNormalizedValue = ((pixelUnnormalizedValue - minLocalPixelValue) * normalizationFactor) + minGlobalPixelValue;

			if (pixelNormalizedValue > maxGlobalPixelValue)
				pixelNormalizedValue = maxGlobalPixelValue;
			if (pixelNormalizedValue < minGlobalPixelValue)
				pixelNormalizedValue = minGlobalPixelValue;

			framePixelsNormalizeds[i] = (byte)pixelNormalizedValue;
		}

		return framePixelsNormalizeds;
	}

	private double GetNormalizationFactor(byte[] framePixels)
	{
		Array.Sort(framePixels);
		int minIndex = (int)(framePixels.Length * minThresholdPercentage);
		int maxIndex = (int)(framePixels.Length * maxThresholdPercentage);
		minLocalPixelValue = framePixels[minIndex];
		maxLocalPixelValue = framePixels[maxIndex];

		normalizationFactor = (maxGlobalPixelValue - minGlobalPixelValue) / (maxLocalPixelValue - minLocalPixelValue);

		return normalizationFactor;
	}

	//Instead of using thresholds to avoid outlayers simply use the maximum and minimum pixel values
	private double GetNormalizationFactorWithoutThreshold(byte[] framePixels)
	{
		for (int i = 0; i < framePixels.Length; i++)
		{
			if (framePixels[i] < minLocalPixelValue)
				minLocalPixelValue = framePixels[i];

			if (framePixels[i] > maxLocalPixelValue)
				maxLocalPixelValue = framePixels[i];
		}

		normalizationFactor = (maxGlobalPixelValue - minGlobalPixelValue) / (maxLocalPixelValue - minLocalPixelValue);

		return normalizationFactor;
	}
}

Again, many thanks for your time!

[dlemstra]

How can I work with memory images (byte[]) instead of static ones? I expected that this library with the new ImageMagcik(byte[]) can do that, but I'm stuck trying to find how to apply convert to those virtual images...

I don't understand what you are asking me. If you want to read a single image you can specify the bytes of the image or the name of the file (and some other methods) as an argument to the MagickImage class.

There is a way with Magick.NET to achieve that?

Still not sure what you are asking?

Why takes so long to perform a -normalize filter?

The duration also depends on the version of ImageMagick that you are using. You are probably using a Q16-HDRI version on the command line. You might want to consider to use the Q8 version of Magick.NET instead. And another thing that might help would be to use the OpenMP version.

And I suspect the duration is longer because we use double precision instead. More info about the implementation can be found here:

https://github.com/ImageMagick/ImageMagick/blob/8c4418952feafa9e5699404005d528a838db046a/MagickCore/enhance.c#L4119

And here:

https://github.com/ImageMagick/ImageMagick/blob/8c4418952feafa9e5699404005d528a838db046a/MagickCore/enhance.c#L1551

4.Why?

See above.

[EricBatlle]

How can I work with memory images (byte[]) instead of static ones? I expected that this library with the new ImageMagcik(byte[]) can do that, but I'm stuck trying to find how to apply convert to those virtual images...

I don't understand what you are asking me. If you want to read a single image you can specify the bytes of the image or the name of the file (and some other methods) as an argument to the MagickImage class.

There is a way with Magick.NET to achieve that?

Still not sure what you are asking?

Why takes so long to perform a -normalize filter?

The duration also depends on the version of ImageMagick that you are using. You are probably using a Q16-HDRI version on the command line. You might want to consider to use the Q8 version of Magick.NET instead. And another thing that might help would be to use the OpenMP version.

Thanks dlmestra for your feedback, but clearly I wasn't clear about my doubts, I'll try again:

1. Does Magick.NET have the ImageMagick "convert" command? If yes, how can I used? Cause I can't find it on Magick.NET repo documentation.
2. The benchmarks that I mention weren't taken with Magick.NET, but with ImageMagick commands (cause as Explained in 1, I don't know how to call convert -normalize from Magick.NET)
3. In case Magick.NET can't perform the convert -normalize command, it is possible to use ImageMagick, from the command line, using byte[] instead of the stored in disk image? How?

And I suspect the duration is longer because we use double precision instead. More info about the implementation can be found here:

https://github.com/ImageMagick/ImageMagick/blob/8c4418952feafa9e5699404005d528a838db046a/MagickCore/enhance.c#L4119

And here:

https://github.com/ImageMagick/ImageMagick/blob/8c4418952feafa9e5699404005d528a838db046a/MagickCore/enhance.c#L1551

Many many thanks for those links, hope this time my questions are better defined :)

[dlemstra]

1. Does Magick.NET have the ImageMagick "convert" command? If yes, how can I used? Cause I can't find it on Magick.NET repo documentation.

It has (almost) all the functionality that is available in the convert executable but it uses a C# api instead.

2. The benchmarks that I mention weren't taken with Magick.NET, but with ImageMagick commands (cause as Explained in 1, I don't know how to call convert -normalize from Magick.NET)

The MagickImage class has Normalize() method that does the same as the -normalize option.

[EricBatlle]

My god, simply as Normalize() that was what I was looking for, typingi "convert.." expecting to autocomplete with some argument or something else...my bad, thanks for your patience dlmestra.