Convert PNG to black/white byte array

[mu88]

Hi 👋🏻

First of all, thank you for your awesome library!

I have a PNG image like this:

To display it on an ePaper display, I need it as a black/white image. Furthermore, I only need a single byte per pixel (representing black or white as 0 resp. 255), not a value per channel per pixel.

I did the b/w conversion like this:

using var image = new MagickImage();
await image.ReadAsync(screenshotFile);

if (blackAndWhite)
{
    image.Alpha(AlphaOption.Off);
    image.Threshold(new Percentage(95));
}

return image.ToByteArray();

That looks okay, but not as crisp like in image processing software like GIMP.

Now I have two questions:

1. In the docs, I found the monochrome option. Where do I find this option in Magick.NET?
2. With my code, I still have an image with three channels, where every pixel of every channel is either 0 or 65536. Of course I could manually process all pixels, discard two channels and replace 65536 by 255.
   But is there a smarter way using one of Magick.NET's APIs for this task?

Thank you!

Versions:

• .NET 7, running on Linux (amd64 and arm64)
• <PackageReference Include="Magick.NET-Q16-AnyCPU" Version="13.1.3" />

[dlemstra]

You are pretty close. Below is an example of what you could do to export the pixels instead:

using var image = new MagickImage();
image.Read(screenshotFile);

if (blackAndWhite)
{
    // Maybe gets you a better result ?
    image.Alpha(AlphaOption.Off);
    image.Threshold(new Percentage(95));

    // This will make your image monochrome.
    image.ColorType = ColorType.Bilevel;
}

// This will export the pixels of the image.
using var pixels = image.GetPixelsUnsafe();
pixels.ToByteArray("R");

[mu88]

thx a lot! So the monochrome option does not explicitly exist in Magick.NET's API, am I getting it correctly?

[dlemstra]

The code behind -monochrome does this: image.ColorType = ColorType.Bilevel;. But I did not want to add an extra method to the API for this.

[mu88]

Ah okay, got it 💪🏻