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C#图片处理基本应用(裁剪,缩放,清晰度,水印)

分类: 文章 • 2025-02-28 15:46:28

C#图片处理基本应用(裁剪,缩放,清晰度,水印)

前言

需求源自项目中的一些应用，比如相册功能，通常用户上传相片后我们都会针对该相片再生成一张缩略图，用于其它页面上的列表显示。随便看一下，大部分网站基本都是将原图等比缩放来生成缩略图。但完美主义者会发现一些问题，比如显示排版时想让相片缩略图列表非常统一、整齐、和美观，比如要求每张缩略图大小固定为120 x 90且不拉伸变形怎么办？再比如用户头像如何让缩略图比原图更清晰？或是如何在上传的图片下加一个半透明的LOGO水印？

OK，本文根据自己的项目代码描述以上问题的解决方案，全部基于.Net Framework类库完成，代码中包含了C#图片处理的一些基础知识，与大家分享，个人能力有限，不足之处还请及时指正。

提高缩略图清晰度

C#图片处理基本应用(裁剪,缩放,清晰度,水印)(原图200*200,12.3k)C#图片处理基本应用(裁剪,缩放,清晰度,水印)(处理后80*80,17.7k)

之前一直认为缩略图不可能比原图清晰，直到某天一位产品的同事给我看某网站的效果。于是开始寻找.NET下实现代码，仔细观察缩略图确实比原图更清晰了一些，但代价是缩略图文件比原图更大，所以如果你想让一张占满显示器屏幕的超大图片更清晰，那么图片占用空间和网络流量就必需考虑了，如果是互联网应用，建议缩略图在200像素以内的使用该方法。当然如果哪位有更好的代码即能让图片文件大小变化不大又让图片更清晰还请分享。

图片裁剪

C#图片处理基本应用(裁剪,缩放,清晰度,水印)(原图256*192)C#图片处理基本应用(裁剪,缩放,清晰度,水印)(裁剪要求100*100)

C#图片处理基本应用(裁剪,缩放,清晰度,水印)(原图256*192)C#图片处理基本应用(裁剪,缩放,清晰度,水印)(裁剪要求90*120)

C#图片处理基本应用(裁剪,缩放,清晰度,水印)(原图256*192)C#图片处理基本应用(裁剪,缩放,清晰度,水印)(裁剪要求120*90)

C#图片处理基本应用(裁剪,缩放,清晰度,水印)(原图146*256)C#图片处理基本应用(裁剪,缩放,清晰度,水印)(裁剪要求100*100)

C#图片处理基本应用(裁剪,缩放,清晰度,水印)(原图146*256)C#图片处理基本应用(裁剪,缩放,清晰度,水印)(裁剪要求90*120)

C#图片处理基本应用(裁剪,缩放,清晰度,水印)(原图146*256)C#图片处理基本应用(裁剪,缩放,清晰度,水印)(裁剪要求120*90)

算法：以原图中心作为裁剪中心，最大范围的对原图进行裁剪，然后对裁剪结果等比缩放。

图片水印

C#图片处理基本应用(裁剪,缩放,清晰度,水印)C#图片处理基本应用(裁剪,缩放,清晰度,水印)

仅演示了效果，如需要变更字体、水印透明度、位置等可自行在代码或方法中扩展。

代码

封装了几个通用的方法，如发现有BUG或漏洞还请及时指正。

view sourceprint?
using System;
using System.Collections.Generic;
using System.Text;
using System.IO;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
  
namespace WuJian.Common
{
    /// <summary>
    /// 图片处理类
    /// 吴剑 2008-07-02 创建
    /// 吴剑 2011-01-21 修改
    /// </summary>
    public class PTImage
    {
        #region 正方型裁剪并缩放
        /// <summary>
        /// 正方型裁剪
        /// 以图片中心为轴心，截取正方型，然后等比缩放
        /// 用于头像处理
        /// </summary>
        /// <remarks>吴剑 2010-11-23</remarks>
        /// <param name="postedFile">原图HttpPostedFile对象</param>
        /// <param name="fileSaveUrl">缩略图存放地址</param>
        /// <param name="side">指定的边长（正方型）</param>
        /// <param name="quality">质量（范围0-100）</param>
        public static void CutForSquare(System.Web.HttpPostedFile postedFile, string fileSaveUrl, int side, int quality)
        {
            //创建目录
            string dir = Path.GetDirectoryName(fileSaveUrl);
            if (!Directory.Exists(dir))
                Directory.CreateDirectory(dir);
  
            //原始图片（获取原始图片创建对象，并使用流中嵌入的颜色管理信息）
            System.Drawing.Image initImage = System.Drawing.Image.FromStream(postedFile.InputStream, true);
  
            //原图宽高均小于模版，不作处理，直接保存
            if (initImage.Width <= side && initImage.Height <= side)
            {
                initImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            else
            {
                //原始图片的宽、高
                int initWidth = initImage.Width;
                int initHeight = initImage.Height;
  
                //非正方型先裁剪为正方型
                if (initWidth != initHeight)
                {
                    //截图对象
                    System.Drawing.Image pickedImage = null;
                    System.Drawing.Graphics pickedG = null;
  
                    //宽大于高的横图
                    if (initWidth > initHeight)
                    {
                        //对象实例化
                        pickedImage = new System.Drawing.Bitmap(initHeight, initHeight);
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
                        //设置质量
                        pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                        pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        //定位
                        Rectangle fromR = new Rectangle((initWidth - initHeight) / 2, 0, initHeight, initHeight);
                        Rectangle toR = new Rectangle(0, 0, initHeight, initHeight);
                        //画图
                        pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);
                        //重置宽
                        initWidth = initHeight;
                    }
                    //高大于宽的竖图
                    else
                    {
                        //对象实例化
                        pickedImage = new System.Drawing.Bitmap(initWidth, initWidth);
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
                        //设置质量
                        pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                        pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        //定位
                        Rectangle fromR = new Rectangle(0, (initHeight - initWidth) / 2, initWidth, initWidth);
                        Rectangle toR = new Rectangle(0, 0, initWidth, initWidth);
                        //画图
                        pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);
                        //重置高
                        initHeight = initWidth;
                    }
  
                    //将截图对象赋给原图
                    initImage = (System.Drawing.Image)pickedImage.Clone();
                    //释放截图资源
                    pickedG.Dispose();
                    pickedImage.Dispose();
                }
  
                //缩略图对象
                System.Drawing.Image resultImage = new System.Drawing.Bitmap(side, side);
                System.Drawing.Graphics resultG = System.Drawing.Graphics.FromImage(resultImage);
                //设置质量
                resultG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                resultG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                //用指定背景色清空画布
                resultG.Clear(Color.White);
                //绘制缩略图
                resultG.DrawImage(initImage, new System.Drawing.Rectangle(0, 0, side, side), new System.Drawing.Rectangle(0, 0, initWidth, initHeight), System.Drawing.GraphicsUnit.Pixel);
  
                //关键质量控制
                //获取系统编码类型数组,包含了jpeg,bmp,png,gif,tiff
                ImageCodecInfo[] icis = ImageCodecInfo.GetImageEncoders();
                ImageCodecInfo ici = null;
                foreach (ImageCodecInfo i in icis)
                {
                    if (i.MimeType == "image/jpeg" || i.MimeType == "image/bmp" || i.MimeType == "image/png" || i.MimeType == "image/gif")
                    {
                        ici = i;
                    }
                }
                EncoderParameters ep = new EncoderParameters(1);
                ep.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)quality);
  
                //保存缩略图
                resultImage.Save(fileSaveUrl, ici, ep);
  
                //释放关键质量控制所用资源
                ep.Dispose();
  
                //释放缩略图资源
                resultG.Dispose();
                resultImage.Dispose();
  
                //释放原始图片资源
                initImage.Dispose();
            }
        }
  
        /// <summary>
        /// 正方型裁剪
        /// 以图片中心为轴心，截取正方型，然后等比缩放
        /// 用于头像处理
        /// </summary>
        /// <remarks>吴剑 2010-11-23</remarks>
        /// <param name="postedFile">原图HttpPostedFile对象</param>
        /// <param name="fileSaveUrl">缩略图存放地址</param>
        /// <param name="side">指定的边长（正方型）</param>
        /// <param name="quality">质量（范围0-100）</param>
        public static void CutForSquare(System.IO.Stream fromFile, string fileSaveUrl, int side, int quality)
        {
            //创建目录
            string dir = Path.GetDirectoryName(fileSaveUrl);
            if (!Directory.Exists(dir))
                Directory.CreateDirectory(dir);
  
            //原始图片（获取原始图片创建对象，并使用流中嵌入的颜色管理信息）
            System.Drawing.Image initImage = System.Drawing.Image.FromStream(fromFile, true);
  
            //原图宽高均小于模版，不作处理，直接保存
            if (initImage.Width <= side && initImage.Height <= side)
            {
                initImage.Save(fileSaveUrl, System.Drawing.Imaging.ImageFormat.Jpeg);
            }
            else
            {
                //原始图片的宽、高
                int initWidth = initImage.Width;
                int initHeight = initImage.Height;
  
                //非正方型先裁剪为正方型
                if (initWidth != initHeight)
                {
                    //截图对象
                    System.Drawing.Image pickedImage = null;
                    System.Drawing.Graphics pickedG = null;
  
                    //宽大于高的横图
                    if (initWidth > initHeight)
                    {
                        //对象实例化
                        pickedImage = new System.Drawing.Bitmap(initHeight, initHeight);
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
                        //设置质量
                        pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                        pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        //定位
                        Rectangle fromR = new Rectangle((initWidth - initHeight) / 2, 0, initHeight, initHeight);
                        Rectangle toR = new Rectangle(0, 0, initHeight, initHeight);
                        //画图
                        pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);
                        //重置宽
                        initWidth = initHeight;
                    }
                    //高大于宽的竖图
                    else
                    {
                        //对象实例化
                        pickedImage = new System.Drawing.Bitmap(initWidth, initWidth);
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);
                        //设置质量
                        pickedG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                        pickedG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                        //定位
                        Rectangle fromR = new Rectangle(0, (initHeight - initWidth) / 2, initWidth, initWidth);
                        Rectangle toR = new Rectangle(0, 0, initWidth, initWidth);
                        //画图
                        pickedG.DrawImage(initImage, toR, fromR, System.Drawing.GraphicsUnit.Pixel);
                        //重置高
                        initHeight = initWidth;
                    }
  
                    //将截图对象赋给原图
                    initImage = (System.Drawing.Image)pickedImage.Clone();
                    //释放截图资源
                    pickedG.Dispose();
                    pickedImage.Dispose();
                }
  
                //缩略图对象
                System.Drawing.Image resultImage = new System.Drawing.Bitmap(side, side);
                System.Drawing.Graphics resultG = System.Drawing.Graphics.FromImage(resultImage);
                //设置质量
                resultG.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                resultG.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                //用指定背景色清空画布
                resultG.Clear(Color.White);
                //绘制缩略图
                resultG.DrawImage(initImage, new System.Drawing.Rectangle(0, 0, side, side), new System.Drawing.Rectangle(0, 0, initWidth, initHeight), System.Drawing.GraphicsUnit.Pixel);
  

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