Provide a collection of the pixels that differ between two images

[MJB222398]

For my use case I compare screenshots taken on Full HD screens (1920 x 1080). The number of pixels different between these can sometimes be very very few, maybe a couple of hundred or even less. I have even had a case where only one pixel differed (it differed only by 4 in the R value, G and B matched. That's not even a needle in a haystack haha. Calculating the difference image to show the differences does not really help with this when there are so few pixels different. I couldn't tell what was a differing pixel and what was just dust on my screen.

When this happens I end up having to investigate manually and debug ImageShare.Compare to find the coordinates of the pixel that differed which of course takes time and is not ideal. I wonder therefore if it would be a good idea to include a collection of all the pixels that differed in the ICompareResult? This might have to be limited to a certain number as the collection could be huge if the images are large and vastly different.

Maybe you have a different and better idea?

[stesee]

Have a look at

ImageSharp.Compare/ImageSharpCompare/ImageSharpCompare.cs

Line 529 in 279b907

public static Image CalcDiffMaskImage(Stream actualImage, Stream expectedImage, ResizeOption resizeOption = ResizeOption.DontResize, int pixelColorShiftTolerance = 0)

The resulting image is a two-dimensional representation of the difference. Pixels with a color that is not zero indicate differences between the actualImage and expectedImage of the call of ImageSharpCompare.CalcDiffMaskImage.

You could write some code like

   [TestCase(pngBlack2x2px, pngBlack4x4px, ResizeOption.Resize)]
        public void ShouldCalcPixelsThatDiffer(string pathPic1, string pathPic2,ResizeOption resizeOption)
        {
            var absolutePathPic1 = Path.Combine(AppContext.BaseDirectory, pathPic1);
            var absolutePathPic2 = Path.Combine(AppContext.BaseDirectory, pathPic2);

            using var absolutePic1 = Image.Load(absolutePathPic1);
            using var absolutePic2 = Image.Load(absolutePathPic2);

            using (var maskImage = (Image<SixLabors.ImageSharp.PixelFormats.Rgb24>)ImageSharpCompare.CalcDiffMaskImage(absolutePic1, absolutePic2, resizeOption))
            {

                 TestContext.WriteLine($"Comparing {pathPic1} and {pathPic2} with resize option {resizeOption}");
   
                for (var x = 0; x < maskImage.Width; x++)
                {
                    for (var y = 0; y < maskImage.Height; y++)
                    {
                        var maskImagePixel = maskImage[x, y];
                        if (maskImagePixel.R != 0 || maskImagePixel.G != 0 || maskImagePixel.B != 0)
                        {
                            Console.WriteLine($"x: {x}, y: {y}, R: {maskImagePixel.R}, G: {maskImagePixel.G}, B: {maskImagePixel.B}");
                        }
                    }
                }
            }
        }

Let me know if that satisfies your case!