public class Caption : ImageUtility
{
    private const string PangoCaptionFormat = "pango:<span font_family=\"Roboto Condensed\" weight=\"bold\">{0}</span>";
    private readonly IMagickImageCollection<byte> _image;

    public Caption(byte[] bImage)
    {
        _image = new MagickImageCollection(bImage);
    }

    public byte[] Top(string caption)
    {
        var captionWidth = _image.First().Width;
        var captionSettings = new MagickReadSettings
        {
            TextGravity = Gravity.Center,
            BackgroundColor = MagickColors.White,
            Width = captionWidth,
            FontPointsize = captionWidth / 13.0
        };

        using (
            var captionImage = new MagickImage(
                string.Format(PangoCaptionFormat, caption),
                captionSettings
            )
        )
        {
            captionImage.Extent(
                new MagickGeometry(
                    new Percentage(100),
                    new Percentage(110)
                ),
                Gravity.Center
            );
            captionImage.RePage();
            for (var i = 0; i < _image.Count; i++)
            {
                var captionedFrameImages = new MagickImageCollection();
                captionImage.Format = _image[i].Format;
                captionedFrameImages.Add(captionImage);
                captionedFrameImages.Add(_image[i]);
                _image[i] = captionedFrameImages.AppendVertically();
            }
        }

        return _image.ToByteArray();
    }
}