winfrom 图片等比例压缩

效果图：

核心代码：

/// <summary>
        /// 等比例缩放图片
        /// </summary>
        /// <param name="bitmap"></param>
        /// <param name="destHeight"></param>
        /// <param name="destWidth"></param>
        /// <returns></returns>
        private static Bitmap ZoomImage(Bitmap bitmap, int destWidth, int destHeight)
        {
            try
            {
                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 = CompositingQuality.HighQuality;
                g.SmoothingMode = SmoothingMode.HighQuality;
                g.InterpolationMode = InterpolationMode.HighQualityBicubic;
                //g.DrawImage(sourImage, new Rectangle((destWidth - width) / 2, (destHeight - height) / 2, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);
                g.DrawImage(sourImage, new Rectangle(12, 0, 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;
            }
        }

　　

Demo下载： https://download.csdn.net/download/u011392711/11144050