Image Compare doesn't work like expected with transparent images

Magick.NET version

Magick.NET-Q16-AnyCPU-11.3.0

Environment (Operating system, version and so on)

Windows 10 - Version 21H1, 19043.1826

Description

I’m not sure if this is an issue of ImageMagick or the .NET version, but the image compare doesn’t work as expected with transparent PNG’s.

public bool ImagesEqual(string img1, string img2)
{
    MagickImage first = new MagickImage(img1);
    MagickImage second = new MagickImage(img2);

    double diff = first.Compare(second, new ErrorMetric());
    Console.WriteLine("Images are equal to: " + diff);

    // If the images are equal = NaN, they should at least be 95% equal
    if (double.IsNaN(diff) || diff >= 0.95)
    {
         return true;
    }
    else
    {
         return false;
    }
}

Steps to Reproduce

Put in the method 2 transparent images

Expected result: A value between 0 and 1 Actual result: A value above 1

[dlemstra]

I am not sure what you are asking and trying to accomplish. Maybe you could ask for more detailed help in the discussions of the @ImageMagick repository and then start a new discussion here if you need help to translate something to C#.

[dlemstra]

I will try to add a unit test before the next release to check if this issue was resolved. Already gave it a try on the command line and got this output:

compare -metric ncc img1.png img2.png null:
0.840183