c#图片缩放图片剪切功能实现(等比缩放)

所谓c#图片处理高级应，多数是基于.net framework类库完成

代码如下:

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
    /// </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>
        /// <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>
        /// <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);

//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();
            }
        }
        #endregion

#region 固定模版裁剪并缩放
        /// <summary>
        /// 指定长宽裁剪
        /// 按模版比例最大范围的裁剪图片并缩放至模版尺寸
        /// </summary>
        /// <param name="postedfile">原图httppostedfile对象</param>
        /// <param name="filesaveurl">保存路径</param>
        /// <param name="maxwidth">最大宽(单位:px)</param>
        /// <param name="maxheight">最大高(单位:px)</param>
        /// <param name="quality">质量（范围0-100）</param>
        public static void cutforcustom(system.web.httppostedfile postedfile, string filesaveurl, int maxwidth, int maxheight, int quality)
        {
            //从文件获取原始图片，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 <= maxwidth && initimage.height <= maxheight)
            {
                initimage.save(filesaveurl, system.drawing.imaging.imageformat.jpeg);
            }
            else
            {
                //模版的宽高比例
                double templaterate = (double)maxwidth / maxheight;
                //原图片的宽高比例
                double initrate = (double)initimage.width / initimage.height;

//原图与模版比例相等，直接缩放
                if (templaterate == initrate)
                {
                    //按模版大小生成最终图片
                    system.drawing.image templateimage = new system.drawing.bitmap(maxwidth, maxheight);
                    system.drawing.graphics templateg = system.drawing.graphics.fromimage(templateimage);
                    templateg.interpolationmode = system.drawing.drawing2d.interpolationmode.high;
                    templateg.smoothingmode = system.drawing.drawing2d.smoothingmode.highquality;
                    templateg.clear(color.white);
                    templateg.drawimage(initimage, new system.drawing.rectangle(0, 0, maxwidth, maxheight), new system.drawing.rectangle(0, 0, initimage.width, initimage.height), system.drawing.graphicsunit.pixel);
                    templateimage.save(filesaveurl, system.drawing.imaging.imageformat.jpeg);
                }
                //原图与模版比例不等，裁剪后缩放
                else
                {
                    //裁剪对象
                    system.drawing.image pickedimage = null;
                    system.drawing.graphics pickedg = null;

//定位
                    rectangle fromr = new rectangle(0, 0, 0, 0);//原图裁剪定位
                    rectangle tor = new rectangle(0, 0, 0, 0);//目标定位

//宽为标准进行裁剪
                    if (templaterate > initrate)
                    {
                        //裁剪对象实例化
                        pickedimage = new system.drawing.bitmap(initimage.width, (int)math.floor(initimage.width / templaterate));
                        pickedg = system.drawing.graphics.fromimage(pickedimage);

//裁剪源定位
                        fromr.x = 0;
                        fromr.y = (int)math.floor((initimage.height - initimage.width / templaterate) / 2);
                        fromr.width = initimage.width;
                        fromr.height = (int)math.floor(initimage.width / templaterate);

//裁剪目标定位
                        tor.x = 0;
                        tor.y = 0;
                        tor.width = initimage.width;
                        tor.height = (int)math.floor(initimage.width / templaterate);
                    }
                    //高为标准进行裁剪
                    else
                    {
                        pickedimage = new system.drawing.bitmap((int)math.floor(initimage.height * templaterate), initimage.height);
                        pickedg = system.drawing.graphics.fromimage(pickedimage);

fromr.x = (int)math.floor((initimage.width - initimage.height * templaterate) / 2);
                        fromr.y = 0;
                        fromr.width = (int)math.floor(initimage.height * templaterate);
                        fromr.height = initimage.height;

tor.x = 0;
                        tor.y = 0;
                        tor.width = (int)math.floor(initimage.height * templaterate);
                        tor.height = initimage.height;
                    }

//设置质量
                    pickedg.interpolationmode = system.drawing.drawing2d.interpolationmode.highqualitybicubic;
                    pickedg.smoothingmode = system.drawing.drawing2d.smoothingmode.highquality;

//裁剪
                    pickedg.drawimage(initimage, tor, fromr, system.drawing.graphicsunit.pixel);

//按模版大小生成最终图片
                    system.drawing.image templateimage = new system.drawing.bitmap(maxwidth, maxheight);
                    system.drawing.graphics templateg = system.drawing.graphics.fromimage(templateimage);
                    templateg.interpolationmode = system.drawing.drawing2d.interpolationmode.high;
                    templateg.smoothingmode = system.drawing.drawing2d.smoothingmode.highquality;
                    templateg.clear(color.white);
                    templateg.drawimage(pickedimage, new system.drawing.rectangle(0, 0, maxwidth, maxheight), new system.drawing.rectangle(0, 0, pickedimage.width, pickedimage.height), 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
                    templateimage.save(filesaveurl, ici, ep);
                    //templateimage.save(filesaveurl, system.drawing.imaging.imageformat.jpeg);

//释放资源
                    templateg.dispose();
                    templateimage.dispose();

pickedg.dispose();
                    pickedimage.dispose();
                }
            }

//释放资源
            initimage.dispose();
        }
        #endregion

#region 等比缩放
        /// <summary>
        /// 图片等比缩放
        /// </summary>
        /// <param name="postedfile">原图httppostedfile对象</param>
        /// <param name="savepath">缩略图存放地址</param>
        /// <param name="targetwidth">指定的最大宽度</param>
        /// <param name="targetheight">指定的最大高度</param>
        /// <param name="watermarktext">水印文字(为""表示不使用水印)</param>
        /// <param name="watermarkimage">水印图片路径(为""表示不使用水印)</param>
        public static void zoomauto(system.web.httppostedfile postedfile, string savepath, system.double targetwidth, system.double targetheight, string watermarktext, string watermarkimage)
        {
            //创建目录
            string dir = path.getdirectoryname(savepath);
            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 <= targetwidth && initimage.height <= targetheight)
            {
                //文字水印
                if (watermarktext != "")
                {
                    using (system.drawing.graphics gwater = system.drawing.graphics.fromimage(initimage))
                    {
                        system.drawing.font fontwater = new font("黑体", 10);
                        system.drawing.brush brushwater = new solidbrush(color.white);
                        gwater.drawstring(watermarktext, fontwater, brushwater, 10, 10);
                        gwater.dispose();
                    }
                }

//透明图片水印
                if (watermarkimage != "")
                {
                    if (file.exists(watermarkimage))
                    {
                        //获取水印图片
                        using (system.drawing.image wrimage = system.drawing.image.fromfile(watermarkimage))
                        {
                            //水印绘制条件：原始图片宽高均大于或等于水印图片
                            if (initimage.width >= wrimage.width && initimage.height >= wrimage.height)
                            {
                                graphics gwater = graphics.fromimage(initimage);

//透明属性
                                imageattributes imgattributes = new imageattributes();
                                colormap colormap = new colormap();
                                colormap.oldcolor = color.fromargb(255, 0, 255, 0);
                                colormap.newcolor = color.fromargb(0, 0, 0, 0);
                                colormap[] remaptable = { colormap };
                                imgattributes.setremaptable(remaptable, coloradjusttype.bitmap);

float[][] colormatrixelements = {
                                   new float[] {1.0f,  0.0f,  0.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  1.0f,  0.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  0.0f,  1.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  0.0f,  0.0f,  0.5f, 0.0f},//透明度:0.5
                                   new float[] {0.0f,  0.0f,  0.0f,  0.0f, 1.0f}
                                };

colormatrix wmcolormatrix = new colormatrix(colormatrixelements);
                                imgattributes.setcolormatrix(wmcolormatrix, colormatrixflag.default, coloradjusttype.bitmap);
                                gwater.drawimage(wrimage, new rectangle(initimage.width - wrimage.width, initimage.height - wrimage.height, wrimage.width, wrimage.height), 0, 0, wrimage.width, wrimage.height, graphicsunit.pixel, imgattributes);

gwater.dispose();
                            }
                            wrimage.dispose();
                        }
                    }
                }

//保存
                initimage.save(savepath, system.drawing.imaging.imageformat.jpeg);
            }
            else
            {
                //缩略图宽、高计算
                double newwidth = initimage.width;
                double newheight = initimage.height;

//宽大于高或宽等于高（横图或正方）
                if (initimage.width > initimage.height || initimage.width == initimage.height)
                {
                    //如果宽大于模版
                    if (initimage.width > targetwidth)
                    {
                        //宽按模版，高按比例缩放
                        newwidth = targetwidth;
                        newheight = initimage.height * (targetwidth / initimage.width);
                    }
                }
                //高大于宽（竖图）
                else
                {
                    //如果高大于模版
                    if (initimage.height > targetheight)
                    {
                        //高按模版，宽按比例缩放
                        newheight = targetheight;
                        newwidth = initimage.width * (targetheight / initimage.height);
                    }
                }

//生成新图
                //新建一个bmp图片
                system.drawing.image newimage = new system.drawing.bitmap((int)newwidth, (int)newheight);
                //新建一个画板
                system.drawing.graphics newg = system.drawing.graphics.fromimage(newimage);

//设置质量
                newg.interpolationmode = system.drawing.drawing2d.interpolationmode.highqualitybicubic;
                newg.smoothingmode = system.drawing.drawing2d.smoothingmode.highquality;

//置背景色
                newg.clear(color.white);
                //画图
                newg.drawimage(initimage, new system.drawing.rectangle(0, 0, newimage.width, newimage.height), new system.drawing.rectangle(0, 0, initimage.width, initimage.height), system.drawing.graphicsunit.pixel);

//文字水印
                if (watermarktext != "")
                {
                    using (system.drawing.graphics gwater = system.drawing.graphics.fromimage(newimage))
                    {
                        system.drawing.font fontwater = new font("宋体", 10);
                        system.drawing.brush brushwater = new solidbrush(color.white);
                        gwater.drawstring(watermarktext, fontwater, brushwater, 10, 10);
                        gwater.dispose();
                    }
                }

//透明图片水印
                if (watermarkimage != "")
                {
                    if (file.exists(watermarkimage))
                    {
                        //获取水印图片
                        using (system.drawing.image wrimage = system.drawing.image.fromfile(watermarkimage))
                        {
                            //水印绘制条件：原始图片宽高均大于或等于水印图片
                            if (newimage.width >= wrimage.width && newimage.height >= wrimage.height)
                            {
                                graphics gwater = graphics.fromimage(newimage);

//透明属性
                                imageattributes imgattributes = new imageattributes();
                                colormap colormap = new colormap();
                                colormap.oldcolor = color.fromargb(255, 0, 255, 0);
                                colormap.newcolor = color.fromargb(0, 0, 0, 0);
                                colormap[] remaptable = { colormap };
                                imgattributes.setremaptable(remaptable, coloradjusttype.bitmap);

float[][] colormatrixelements = {
                                   new float[] {1.0f,  0.0f,  0.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  1.0f,  0.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  0.0f,  1.0f,  0.0f, 0.0f},
                                   new float[] {0.0f,  0.0f,  0.0f,  0.5f, 0.0f},//透明度:0.5
                                   new float[] {0.0f,  0.0f,  0.0f,  0.0f, 1.0f}
                                };

colormatrix wmcolormatrix = new colormatrix(colormatrixelements);
                                imgattributes.setcolormatrix(wmcolormatrix, colormatrixflag.default, coloradjusttype.bitmap);
                                gwater.drawimage(wrimage, new rectangle(newimage.width - wrimage.width, newimage.height - wrimage.height, wrimage.width, wrimage.height), 0, 0, wrimage.width, wrimage.height, graphicsunit.pixel, imgattributes);
                                gwater.dispose();
                            }
                            wrimage.dispose();
                        }
                    }
                }

//保存缩略图
                newimage.save(savepath, system.drawing.imaging.imageformat.jpeg);

//释放资源
                newg.dispose();
                newimage.dispose();
                initimage.dispose();
            }
        }

#endregion

#region 其它
        /// <summary>
        /// 判断文件类型是否为web格式图片
        /// (注：jpg,gif,bmp,png)
        /// </summary>
        /// <param name="contenttype">httppostedfile.contenttype</param>
        /// <returns></returns>
        public static bool iswebimage(string contenttype)
        {
            if (contenttype == "image/pjpeg" || contenttype == "image/jpeg" || contenttype == "image/gif" || contenttype == "image/bmp" || contenttype == "image/png")
            {
                return true;
            }
            else
            {
                return false;
            }
        }

#endregion
    }//end class
}