使用Graphics 保存 图片质量很差，怎么回事？

Question

原本宽度为300 的图片ImagePhoto 大小为 30KB FixedSize(ImagePhoto,300) 之后 图片 变为 20KB 了，图片质量下降了很多 怎么弄让图片质量和原来的一样呢？ public static Image FixedSize(Image imgPhoto, int Width) { int sourceWidth = imgPhoto.Width; int sourceHeight = imgPhoto.Height; int w, h; if (sourceWidth > Width) { decimal nPercent = (decimal)sourceWidth / Width; w = Width; h = (int)Math.Round((decimal)sourceHeight / nPercent, 0); } else { w = sourceWidth; h = sourceHeight; } Bitmap bmPhoto = new Bitmap(w, h, imgPhoto.PixelFormat); bmPhoto.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution); Graphics grPhoto = Graphics.FromImage(bmPhoto); grPhoto.CompositingQuality = CompositingQuality.HighQuality; grPhoto.SmoothingMode = SmoothingMode.HighQuality; grPhoto.InterpolationMode = InterpolationMode.HighQualityBicubic; grPhoto.DrawImage(imgPhoto, new Rectangle(0, 0, w, h), new Rectangle(0, 0, sourceWidth, sourceHeight), GraphicsUnit.Pixel); grPhoto.Dispose(); return bmPhoto; }

Answer 1

如果是JPG的话，参考以下代码：

var imageCodeInfo = GetEncoderInfo("image/jpeg");
var myEncoder = System.Drawing.Imaging.Encoder.Quality;
var myEncoderParameters = new EncoderParameters(1);
var myEncoderParameters.Param[0] = new EncoderParameter(myEncoder, 99L);
thumbNail.Save(thumbUrl, imageCodeInfo, myEncoderParameters);