自定义裁剪图片

判断图片大小，根据裁剪目标对图片进行缩放，然后裁剪图片（在图像不变形情况下）

        /// <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="fromFile">原图Stream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(Image initImage, 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(fromFile, 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)System.Math.Floor(initImage.Width / templateRate));
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);

                        //裁剪源定位
                        fromR.X = 0;
                        fromR.Y = (int)System.Math.Floor((initImage.Height - initImage.Width / templateRate) / 2);
                        fromR.Width = initImage.Width;
                        fromR.Height = (int)System.Math.Floor(initImage.Width / templateRate);

                        //裁剪目标定位
                        toR.X = 0;
                        toR.Y = 0;
                        toR.Width = initImage.Width;
                        toR.Height = (int)System.Math.Floor(initImage.Width / templateRate);
                    }
                    //高为标准进行裁剪
                    else
                    {
                        pickedImage = new System.Drawing.Bitmap((int)System.Math.Floor(initImage.Height * templateRate), initImage.Height);
                        pickedG = System.Drawing.Graphics.FromImage(pickedImage);

                        fromR.X = (int)System.Math.Floor((initImage.Width - initImage.Height * templateRate) / 2);
                        fromR.Y = 0;
                        fromR.Width = (int)System.Math.Floor(initImage.Height * templateRate);
                        fromR.Height = initImage.Height;

                        toR.X = 0;
                        toR.Y = 0;
                        toR.Width = (int)System.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();
        }

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