How to get diff of two images?

[pigLoveRabbit520]

Two images, same size, I want to calculate the rgb value difference of every pixel, any built-in method?

[dlemstra]

You could use the Compare method of MagickImage for this?

[pigLoveRabbit520]

Compare is not what I want, I want the method like this

private static MagickImage imageDiff(IPixelCollection pc1, IPixelCollection pc2, int width, int height)
{
var result = new MagickImage(MagickColor.FromRgb(0, 0, 0), width, height);

for (int x = 0; x < width; x++)
{
    for (int y = 0; y < height; y++)
    {
        var p1 = pc1[x, y];
        var p2 = pc2[x, y];

        var arr1 = p1.ToArray();
        var arr2 = p2.ToArray();

        var span = new ushort[4];
        for (int i = 0; i < span.Length; i++)
        {
            var tmp = arr1[i] - arr2[i];
            if (tmp <= 0)
            {
                tmp = 0;
            }
            span[i] = Convert.ToUInt16(tmp);
        }
        
        result.GetPixels().SetPixel(x, y, span);
    }
}
return result;

}

[pigLoveRabbit520]

this method implemented by myself is ok, however, it's slow...

private static MagickImage imageDiff(IPixelCollection<ushort> pc1, IPixelCollection<ushort> pc2, int width, int height)
{
    var result = new MagickImage(MagickColor.FromRgb(0, 0, 0), width, height);

    for (int x = 0; x < width; x++)
    {
        for (int y = 0; y < height; y++)
        {
            var p1 = pc1[x, y];
            var p2 = pc2[x, y];

            var arr1 = p1.ToArray();
            var arr2 = p2.ToArray();

            var span = new ushort[4];
            for (int i = 0; i < span.Length; i++)
            {
                var tmp = arr1[i] - arr2[i];
                if (tmp <= 0)
                {
                    tmp = 0;
                }
                span[i] = Convert.ToUInt16(tmp);
            }
            
            result.GetPixels().SetPixel(x, y, span);
        }
    }
    return result;
}

[dlemstra]

You should get an improvement when you do result.GetPixels() only once and result.GetPixelsUnsafe() should be even faster.

But it should also be possible to use the -fx operator on multiple images (https://imagemagick.org/script/fx.php). That feature is not yet available in this library and I think we will need to and an extra overload to MagickImage.Fx to make this possible.

[dlemstra]

The Fx will become available for the MagickImageCollection in the next release.