C image compression method

In the web application, the images submitted by the client must be compressed. Especially for large images, if they are not compressed, the page will become very large and slow to open. Of course, if you need high-quality images, you also need to produce thumbnails.

Here is the image compression algorithm I have been thinking about. First of all, this is a simple implementation without optimization:

public static System.Drawing.Image GetImageThumb(System.Drawing.Image sourceImg, int width, int height)
        {
            System.Drawing.Image targetImg = new System.Drawing.Bitmap(width, height);
            using (System.Drawing.Graphics g = System.Drawing.Graphics.FromImage(targetImg))
            {
                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
                g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
                g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
                g.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
                g.DrawImage(sourceImg, new System.Drawing.Rectangle(0, 0, width, height), new System.Drawing.Rectangle(0, 0, sourceImg.Width, sourceImg.Height), System.Drawing.GraphicsUnit.Pixel);
                g.Dispose();
            }
            return targetImg;
        }

This method is relatively simple and USES high quality compression. After this compression, the 200K image can only be compressed to about 160k. After rewriting the code to achieve the following method:

public Bitmap GetImageThumb(Bitmap mg, Size newSize)
        {
            double ratio = 0d;
            double myThumbWidth = 0d;
            double myThumbHeight = 0d;
            int x = 0;
            int y = 0;
            Bitmap bp;
            if ((mg.Width / Convert.ToDouble(newSize.Width)) > (mg.Height /
            Convert.ToDouble(newSize.Height)))
                ratio = Convert.ToDouble(mg.Width) / Convert.ToDouble(newSize.Width);
            else
                ratio = Convert.ToDouble(mg.Height) / Convert.ToDouble(newSize.Height);
            myThumbHeight = Math.Ceiling(mg.Height / ratio);
            myThumbWidth = Math.Ceiling(mg.Width / ratio);
            Size thumbSize = new Size((int)newSize.Width, (int)newSize.Height);
            bp = new Bitmap(newSize.Width, newSize.Height);
            x = (newSize.Width - thumbSize.Width) / 2;
            y = (newSize.Height - thumbSize.Height);
            System.Drawing.Graphics g = Graphics.FromImage(bp);
            g.SmoothingMode = SmoothingMode.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.PixelOffsetMode = PixelOffsetMode.HighQuality;
            Rectangle rect = new Rectangle(x, y, thumbSize.Width, thumbSize.Height);
            g.DrawImage(mg, rect, 0, 0, mg.Width, mg.Height, GraphicsUnit.Pixel);
            return bp;
        }

The compression achieved in this way greatly increases the compression rate. In fact, the code has not changed much, the most important thing is that if you use the jpg format when saving, if you do not specify the format, the default is to use the png format.

The following is the method of compressing pictures according to the setting of image quality value written by gardeners:

public static bool GetPicThumbnail(string sFile, string outPath, int flag)
        {
            System.Drawing.Image iSource = System.Drawing.Image.FromFile(sFile);
            ImageFormat tFormat = iSource.RawFormat;
            // The following code sets the compression quality when saving the image   
            EncoderParameters ep = new EncoderParameters();
            long[] qy = new long[1];
            qy[0] = flag;// Set the ratio of compression 1-100  
            EncoderParameter eParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qy);
            ep.Param[0] = eParam;
            try
            {
                ImageCodecInfo[] arrayICI = ImageCodecInfo.GetImageEncoders();
                ImageCodecInfo jpegICIinfo = null;
                for (int x = 0; x < arrayICI.Length; x++)
                {
                    if (arrayICI[x].FormatDescription.Equals("JPEG"))
                    {
                        jpegICIinfo = arrayICI[x];
                        break;
                    }
                }
                if (jpegICIinfo != null)
                {
                    iSource.Save(outPath, jpegICIinfo, ep);//dFile Is the compressed new path   
                }
                else
                {
                    iSource.Save(outPath, tFormat);
                }
                return true;
            }
            catch
            {
                return false;
            }
            finally
            {
                iSource.Dispose();
                iSource.Dispose();
            }
        }

Reprinted source: http: / / www cnblogs. com lifeil/archive 2013/02/25/2931683. html