c# 图片按比例缩放

public static Bitmap GetThumbnail(Bitmap b, int destHeight, int destWidth) { System.Drawing.Image imgSource = b; System.Drawing.Imaging.ImageFormat thisFormat = imgSource.RawFormat; int sW = 0, sH = 0; // 按比例缩放 int sWidth = imgSource.Width; int sHeight = imgSource.Height; if (sHeight > destHeight || sWidth > destWidth) { if ((sWidth * destHeight) > (sHeight * destWidth)) { sW = destWidth; sH = (destWidth * sHeight) / sWidth; } else { sH = destHeight; sW = (sWidth * destHeight) / sHeight; } } else { sW = sWidth; sH = sHeight; } Bitmap outBmp = new Bitmap(destWidth, destHeight); Graphics g = Graphics.FromImage(outBmp); 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(imgSource, new Rectangle((destWidth - sW) / 2, (destHeight - sH) / 2, sW, sH), 0, 0, imgSource.Width, imgSource.Height, GraphicsUnit.Pixel); g.Dispose(); // 以下代码为保存图片时，设置压缩质量 EncoderParameters encoderParams = new EncoderParameters(); long [] quality = new long [1]; quality[0] = 100; EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality); encoderParams.Param[0] = encoderParam; imgSource.Dispose(); return outBmp; }