Asp.net 上传图片添半透明图片或文字水印的方法（一）

主要用到System.Drawing 命名空间下的相关类，如Brush、Image、Bitmap、Graphics等等类

Image类可以从图片文件创建Image的实例，Bitmap可以从文件也可以从已有的Image对象创建实例，而Graphics类则是封装了对图像的相关操作，可以理解为一个绘图的面板，在这个面板里你可以添加文字，添加背景等等很多常规绘图软件具备的功能。

下面就怎样添加水印做简单的介绍：

为了方便理解我把水印分为文字型的水印以及图片型的水印，它们都派生自WatermarkPainter基类，需要实现基类中的AddWatermark的方法，这个方法是用来具体的绘图用。

WatermarkPainter类如下：

 

using System.Drawing;
using System.IO;
using System.Text;
using System;

namespace Juice.Common.Drawing
{
    /// <summary>
    /// 图片水印绘制器
    /// </summary>
    public abstract class WatermarkPainter : IDisposable
    {
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="rawImagePath"></param>
        /// <param name="alpha"></param>
        /// <param name="replaceRawImage"></param>
        protected WatermarkPainter(string rawImagePath, int alpha, bool replaceRawImage)
        {
            ImageToBePainted = rawImagePath;
            WatermarkAlpha = alpha;
            ReplaceRawImage = replaceRawImage;
        }

        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="rawImagePath"></param>
        /// <param name="alpha"></param>
        protected WatermarkPainter(string rawImagePath, int alpha)
            : this(rawImagePath, alpha, true)
        { }

        /// <summary>
        /// 为临时存储文件添加的后缀
        /// </summary>
        private string m_TempFileSuffix = ".juice.watermark.temp";

        /// <summary>
        /// 水印的透明度
        /// </summary>
        private int m_WatermarkAlpha;

        /// <summary>
        /// 水印透明度
        /// </summary>
        public int WatermarkAlpha
        {
            get
            {
                if (m_WatermarkAlpha > 255)
                    m_WatermarkAlpha = 255;
                else if (m_WatermarkAlpha < 0)
                    m_WatermarkAlpha = 0;
                return m_WatermarkAlpha;
            }
            set { m_WatermarkAlpha = value; }
        }

        private string m_ImageToBePainted;

        /// <summary>
        /// 添加水印的图片的物理路径
        /// </summary>
        public string ImageToBePainted
        {
            get { return m_ImageToBePainted; }
            set { m_ImageToBePainted = value; }
        }

        private bool m_ReplaceRawImage;

        /// <summary>
        /// 是否用加了水印的图片替换原有的图片
        /// </summary>
        public bool ReplaceRawImage
        {
            get { return m_ReplaceRawImage; }
            set { m_ReplaceRawImage = value; }
        }

        private string m_TempImagePath;

        /// <summary>
        /// 加了水印后的临时储存名称
        /// </summary>
        protected string TempImagePath
        {
            get
            {
                if (string.IsNullOrEmpty(this.m_TempImagePath))
                {
                    StringBuilder s = new StringBuilder(ImageToBePainted);
                    s.Append(this.m_TempFileSuffix);
                    this.m_TempImagePath = s.ToString();
                }
                return m_TempImagePath;
            }
            set { m_TempImagePath = value; }
        }

        /// <summary>
        /// 原始图像
        /// </summary>
        private Image m_RawImage;

        /// <summary>
        /// 为图片添加水印
        /// </summary>
        public void PaintWaterMark()
        {
            if (string.IsNullOrEmpty(ImageToBePainted))
                return;
            if (!System.IO.File.Exists(ImageToBePainted))
                throw new FileNotFoundException(string.Format("file {0} not found.", ImageToBePainted));
            bool succeed;
            if (m_RawImage == null)
                m_RawImage = Image.FromFile(ImageToBePainted);
            ///原始的图片
            using (Bitmap newImage = new Bitmap(m_RawImage.Width, m_RawImage.Height))
            {
                ///创建绘制图片的图面
                using (Graphics g = Graphics.FromImage(newImage))
                {
                    g.DrawImage(m_RawImage, 0, 0, m_RawImage.Width, m_RawImage.Height);
                    ///开始绘制水印