图片缩放

/// <summary>
        /// 按比例缩放,图片不会变形，会优先满足原图和最大长宽比例最高的一项
        /// </summary>
        /// <param name="oldPath"></param>
        /// <param name="newPath"></param>
        /// <param name="maxWidth"></param>
        /// <param name="maxHeight"></param>
        public static void CompressPercent(string oldPath, string newPath, int maxWidth, int maxHeight)
        {
            Image _sourceImg = Image.FromFile(oldPath);
            double _newW = (double)maxWidth;
            double _newH = (double)maxHeight;
            double percentWidth = (double)_sourceImg.Width > maxWidth ? (double)maxWidth : (double)_sourceImg.Width;

            if ((double)_sourceImg.Height * (double)percentWidth / (double)_sourceImg.Width > (double)maxHeight)
            {
                _newH = (double)maxHeight;
                _newW = (double)maxHeight / (double)_sourceImg.Height * (double)_sourceImg.Width;
            }
            else
            {
                _newW = percentWidth;
                _newH = (percentWidth / (double)_sourceImg.Width) * (double)_sourceImg.Height;
            }
            Image bitmap = new Bitmap((int)_newW, (int)_newH);
            Graphics g = Graphics.FromImage(bitmap);
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            g.Clear(Color.Transparent);
            g.DrawImage(_sourceImg, new Rectangle(0, 0, (int)_newW, (int)_newH), new Rectangle(0, 0, _sourceImg.Width, _sourceImg.Height), GraphicsUnit.Pixel);
            _sourceImg.Dispose();
            g.Dispose();
            bitmap.Save(newPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            bitmap.Dispose();
        }

        /// <summary>
        /// 按照指定大小对图片进行缩放，可能会图片变形
        /// </summary>
        /// <param name="oldPath"></param>
        /// <param name="newPath"></param>
        /// <param name="newWidth"></param>
        /// <param name="newHeight"></param>
        public static void ImageChangeBySize(string oldPath, string newPath, int newWidth, int newHeight)
        {
            Image sourceImg = Image.FromFile(oldPath);
            System.Drawing.Image bitmap = new System.Drawing.Bitmap(newWidth, newHeight);
            Graphics g = Graphics.FromImage(bitmap);
            g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            g.Clear(Color.Transparent);
            g.DrawImage(sourceImg, new Rectangle(0, 0, newWidth, newHeight), new Rectangle(0, 0, sourceImg.Width, sourceImg.Height), GraphicsUnit.Pixel);
            sourceImg.Dispose();
            g.Dispose();
            bitmap.Save(newPath, System.Drawing.Imaging.ImageFormat.Jpeg);
            bitmap.Dispose();
        }