Determine if Alpha Channel is Used in an Image

Question

As I\'m bringing in images into my program, I want to determine if:

1. they have an alpha-channel
2. if that alpha-channel is used

#1

Answer 1

While I know the OP is not about MagickNet, it might help s/o.

Magick.Net provides a wrapper around Imagick lib and includes a feature to easily access channel statistics.

Example

    public bool HasTransparentBackground(MagickImage image)
    {
        if (!image.HasAlpha) return false;

        var statistics = image.Statistics();
        var alphaStats = statistics.GetChannel(PixelChannel.Alpha);

        var alphaMax = Math.Pow(2, alphaStats.Depth);
        return alphaStats.Minimum < alphaMax * .2;
    }

We first check if the image supports transparency an return if not. Then we get statistics for alpha channel and can simply check the Min property. There's also a Mean property that allows you to check "how much transparent" your image is.

See also

• Detect Alpha Channel with ImageMagick
• https://github.com/dlemstra/Magick.NET