C# Image 图片缩放 截取

从大图中截取一部分图片

        /// <summary>
        /// 从大图中截取一部分图片
        /// </summary>
        /// <param name="fromImage">来源图片</param>        
        /// <param name="offsetX">从偏移X坐标位置开始截取</param>
        /// <param name="offsetY">从偏移Y坐标位置开始截取</param>
        /// <param name="width">新图片的宽度</param>
        /// <param name="height">新图片的高度</param>
        /// <returns></returns>
        public Bitmap CaptureImage(Image fromImage, int offsetX, int offsetY, int width, int height)
        {

            //创建新图位图
            Bitmap bitmap = new Bitmap(width, height);
            //创建作图区域
            Graphics graphic = Graphics.FromImage(bitmap);
            //截取原图相应区域写入作图区
            graphic.DrawImage(fromImage, 0, 0, new Rectangle(offsetX, offsetY, width, height), GraphicsUnit.Pixel);
            //从作图区生成新图
            Bitmap newImage = Image.FromHbitmap(bitmap.GetHbitmap());

            return newImage;

            //保存图片
            //saveImage.Save(toImagePath, ImageFormat.Png);
            //saveImage.Dispose();
            //graphic.Dispose();
            //bitmap.Dispose();
        }
       

等比例缩放图片

private Bitmap ZoomImage(Bitmap bitmap, int destHeight, int destWidth)
        {
            try
            {
                System.Drawing.Image sourImage = bitmap;
                int width = 0, height = 0;
                //按比例缩放           
                int sourWidth = sourImage.Width;
                int sourHeight = sourImage.Height;
                if (sourHeight > destHeight || sourWidth > destWidth)
                {
                    if ((sourWidth * destHeight) > (sourHeight * destWidth))
                    {
                        width = destWidth;
                        height = (destWidth * sourHeight) / sourWidth;
                    }
                    else
                    {
                        height = destHeight;
                        width = (sourWidth * destHeight) / sourHeight;
                    }
                }
                else
                {
                    width = sourWidth;
                    height = sourHeight;
                }
                Bitmap destBitmap = new Bitmap(destWidth, destHeight);
                Graphics g = Graphics.FromImage(destBitmap);
                g.Clear(Color.Transparent);
                //设置画布的描绘质量         
                g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                g.DrawImage(sourImage, new Rectangle((destWidth - width) / 2, (destHeight - height) / 2, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);
                g.Dispose();
                //设置压缩质量     
                System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();
                long[] quality = new long[1];
                quality[0] = 100;
                System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
                encoderParams.Param[0] = encoderParam;
                sourImage.Dispose();
                return destBitmap;
            }
            catch
            {
                return bitmap;
            }
        }