C#实现为Excel添加水印的两种方案对比

Install-Package FreeSpire.XLS

dotnet add package FreeSpire.XLS

using Spire.Xls;
using System.Drawing;
namespace AddWatermarkToExcelUsingHeader
{
    class Program
    {
        static void Main(string[] args)
        {
            // 创建 Workbook 对象
            Workbook workbook = new Workbook();
            // 加载 Excel 文档
            workbook.LoadFromFile(@"C:\Users\Administrator\Desktop\Input.xlsx");
            // 加载水印图片
            Image image = Image.FromFile(@"C:\Users\Administrator\Desktop\confidential.png");
            // 遍历文档中所有工作表
            for (int i = 0; i < workbook.Worksheets.Count; i++)
            {
                // 获取指定工作表
                Worksheet worksheet = workbook.Worksheets[i];
                // 在页眉中央插入图片占位符
                worksheet.PageSetup.CenterHeader = "&G";
                // 将图片设置到页眉中央
                worksheet.PageSetup.CenterHeaderImage = image;
            }
            // 保存结果文件
            workbook.SaveToFile("AddWatermark.xlsx", ExcelVersion.Version2016);
            // 释放资源
            workbook.Dispose();
        }
    }
}

using Spire.Xls;
using System.Drawing;
namespace AddWatermarkToExcelUsingBackground
{
    class Program
    {
        static void Main(string[] args)
        {
            // 创建 Workbook 对象
            Workbook workbook = new Workbook();
            // 加载 Excel 文档
            workbook.LoadFromFile(@"C:\Users\Administrator\Desktop\Input.xlsx");
            // 加载水印图片
            Bitmap bitmapImage = new Bitmap(Image.FromFile(@"C:\Users\Administrator\Desktop\sample.png"));
            // 遍历文档中所有工作表
            for (int i = 0; i < workbook.Worksheets.Count; i++)
            {
                // 获取指定工作表
                Worksheet worksheet = workbook.Worksheets[i];
                // 将图片设置为该工作表的背景
                worksheet.PageSetup.BackgroundImage = bitmapImage;
            }
            // 保存结果文件
            workbook.SaveToFile("AddWatermark.xlsx", ExcelVersion.Version2016);
            // 释放资源
            workbook.Dispose();
        }
    }
}

using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
public static class ChineseWatermarkHelper
{
    /// <summary>
    /// 生成中文文字水印图片（透明背景，倾斜 -30°）
    /// </summary>
    /// <param name="text">水印文本，如 "机密资料"</param>
    /// <param name="width">画布宽度</param>
    /// <param name="height">画布高度</param>
    /// <returns>带有透明背景的 Bitmap 对象</returns>
    public static Bitmap Create(string text, int width, int height)
    {
        Bitmap bmp = new Bitmap(width, height, PixelFormat.Format32bppArgb);
        using (Graphics g = Graphics.FromImage(bmp))
        {
            g.Clear(Color.Transparent);
            g.SmoothingMode = SmoothingMode.AntiAlias;
            g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAliasGridFit;
            using (Font font = new Font("Microsoft YaHei", 60, FontStyle.Bold))
            using (SolidBrush brush = new SolidBrush(Color.FromArgb(60, Color.Red)))
            {
                // 计算文字尺寸并居中
                SizeF size = g.MeasureString(text, font);
                // 平移到画布中心，再旋转，使绘制出的文字位于中央
                g.TranslateTransform(width / 2f, height / 2f);
                g.RotateTransform(-30);
                g.DrawString(text, font, brush, -size.Width / 2f, -size.Height / 2f);
            }
        }
        return bmp;
    }
}

// 生成中文文字水印图片
Bitmap watermarkImage = ChineseWatermarkHelper.Create("机密资料", 800, 600);
// 用作工作表背景水印
workbook.Worksheets[0].PageSetup.BackgroundImage = watermarkImage;