resize an image from byte[] to byte[] may lose pixels #444

public override byte[] Scale(double scaleFactor, String format)
{
    this.ThrowIfDisposed();
    if (scaleFactor <= 0)
    {
        throw new ArgumentException("scalefactor must be greate than 0", nameof(scaleFactor));
    }
    try
    {
        int width = (int)(this.Profile.PixelWidth * scaleFactor);
        int height = (int)(this.Profile.PixelHeight * scaleFactor);
        using (Image<Rgba32> bitmap = Image.Load(_imageData, out IImageFormat imageFormat))
        {
            bitmap.Mutate(x => x.Resize(width, height));
            IImageFormat f = String.IsNullOrWhiteSpace(format) ? imageFormat : GetImageFormat(format);
            using (MemoryStream stream = new MemoryStream())
            {
                bitmap.Save(stream, f);
                        
                stream.Position = 0;
                return stream.ToArray();
            }
        }
    }
    catch (Exception ex)
    {
        throw new ImagingException("scale error.", ex);
    }
}


private IImageFormat GetImageFormat(string format)
{
    IImageFormat imageFormat = SixLabors.ImageSharp.Configuration.Default.FindFormatByFileExtension(format);
    if (imageFormat == null)
    {
        throw new ImagingException($"unsupported format：{format}。");
    }
    return imageFormat;
}