Question

I’m resizing jpegs by using the Graphics.DrawImage method (see code fragment below). Can anyone confirm that this will not affect the compression of the new image? I have seen this thread, but I am talking specifically about compression of jpegs.

    private byte[] getResizedImage(String url, int newWidth)     {         Bitmap bmpOut = null;         System.IO.MemoryStream outStream = new System.IO.MemoryStream();          //input image is disposable         using (Bitmap inputImage = LoadImageFromURL(url))         {             ImageFormat format = inputImage.RawFormat;             decimal ratio;  //ratio old width:new width             int newHeight = 0;              //*** If the image is smaller than a thumbnail just return it             if (inputImage.Width < newWidth)                 return null;              ratio = (decimal)newWidth / inputImage.Width;             decimal h = inputImage.Height * ratio;             newHeight = (int)h;              bmpOut = new Bitmap(newWidth, newHeight);             Graphics g = Graphics.FromImage(bmpOut);             g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;             // try testing with following options:             //g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;             //g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;             //g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;             //g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;              g.FillRectangle(Brushes.White, 0, 0, newWidth, newHeight);             g.DrawImage(inputImage, 0, 0, newWidth, newHeight);             bmpOut.Save(outStream, getImageFormat(url));         }          return outStream.ToArray();      } 

Answer 1

When you call ‘bmpOut.Save’ you have to pass in some EncoderParameters to tell the method what quality level you would like to save it with.

http://msdn.microsoft.com/en-us/library/system.drawing.imaging.encoderparameters(VS.80).aspx