Make part of an image transparent.

[Surfrat]

Hi.

Trying to make a background transparent. Modifying one of your samples with this:

static void Main(string[] args)
{
        System.IO.Directory.CreateDirectory("output");

        using (Image image = Image.Load("fb.jpg"))
        {
            float threshold = 0.5F;
            Color sourceColor = Color.FromRgb(106, 107, 99);
            //Color sourceColor = Color.White;
            Color targetColor = Color.Transparent;
            RecolorBrush brush2 = new RecolorBrush(sourceColor, targetColor, threshold);
            image.Mutate(x => x.Fill(brush2));
            image.Save("output/fb.png");
        }
    }

Not working as yet. Am I on the right track?

Thanks.

[Surfrat]

I figured out a solution:

        [Test]
        [Explicit]
        public void TestMakeImageBackgroundTransparentForShirt1()
        {
            string fileName = "DressMe.Tests.Images.Shirt1.jpg";
            Stream stream = GetEmbeddedImage(fileName);

            if (stream != null)
            {
                Image image = Image.Load<Rgba32>(stream);

                float threshold = 0.1F;
                Color sourceColor = Color.White;
                Color targetColor = Color.Transparent;
                RecolorBrush brush2 = new RecolorBrush(sourceColor, targetColor, threshold);

                image.Mutate(i => i.Clear(brush2));

                SaveToPng(_testImageFilename, image);
                ShowImage(_testImageFilename);
            }
        }

and

public static class ImageExtensions
    {
        public static void Clear(this IImageProcessingContext source, RecolorBrush brush)
        {
            GraphicsOptions graphicsOptions = new GraphicsOptions
            {
                AlphaCompositionMode = PixelAlphaCompositionMode.Clear,
                //ColorBlendingMode = PixelColorBlendingMode.Normal
            };
            source.Fill(graphicsOptions, brush);
        }
    }

Source:

Result:

Not perfect as the logo is also removed:

But good enough for now...

[JimBobSquarePants]

@tocsoft Is there a way this can be made easier? I.E Set the AlphaCompositionMode to Clear by default?

[Surfrat]

It turns out the ImageExtensions are not required.

[JimBobSquarePants]

I don’t understand. You mean you didn’t have to set the AlphaCompositionMode?

[Surfrat]

Yes, I was testing and commented out all the ImageExtensions code. Worked without it.

Here is my final test:

        [Explicit]
        public async Task TestMakeImageBackgroundTransparentForShirt1()
        {
            string fileName = "DressMe.Tests.Images.Shirt1.jpg";
            Stream stream = GetEmbeddedImage(fileName);

            if (stream != null)
            {
                Image image = Image.Load<Rgba32>(stream);

                float threshold = 0.1F;
                Color sourceColor = Color.White;
                Color targetColor = Color.Transparent;
                RecolorBrush brush = new RecolorBrush(sourceColor, targetColor, threshold);

                image.Mutate(context => context.Clear(brush));

                SaveToPng(_testImageFilename, image);
                ShowImage(_testImageFilename);
                await HideImageAsync();
            }
        }