I have to compress the PNG file image, without losing the quality

Question

I want to compress a PNG image, to reduce its size but the quality should remain the same. I have tried to compress JPEG picture. Picture compressed about 90% and quality remain the same but when i compress a PNG image with it. No result, no compression. Same size.

Here is my code.

public const string _StatusLog = "StatusLog.csv";
        static void Main(string[] args)
        {
            Console.WriteLine("                 ###   WELCOME   ###");
            Console.Write("\n\nPlease enter image folder path :");
            string imagePath = Console.ReadLine();
            Program p = new Program();
            p.VaryQualityLevel(imagePath);
            Console.ReadLine();
        }
        private void VaryQualityLevel(string pathOfImage)
        {
            try
            {
                //Console.Write("Target Directory Path :");
                string targetDirectory = pathOfImage;//Console.ReadLine();

                if (targetDirectory != null)
                {
                    string[] allDirectoryInTargetDirectory = Directory.GetDirectories(targetDirectory);
                    //PRODUCT DIRECOTY OPEN
                    Console.Write("Total Folders found = " + allDirectoryInTargetDirectory.Count());
                    Console.Read();
                    if (allDirectoryInTargetDirectory.Any())
                    {
                        foreach (var directory in allDirectoryInTargetDirectory)
                        {
                            string[] subDirectory = Directory.GetDirectories(directory); // ATTRIBUTE DIRECTORY OPEN
                            if (subDirectory.Any())
                            {
                                foreach (var filesInSubDir in subDirectory)
                                {
                                    string[] allFilesInSubDir = Directory.GetFiles(filesInSubDir);
                                    //FILES IN SUB DIR OPEN
                                    if (allFilesInSubDir.Any())
                                    {
                                        foreach (var imageFile in allFilesInSubDir)
                                        {
                                            try
                                            {
                                                Bitmap bmp1 = new Bitmap(imageFile);//pathOfImage);
                                                ImageCodecInfo jpgEncoder = GetEncoder(ImageFormat.Jpeg);

                                                // Create an Encoder object based on the GUID 
                                                // for the Quality parameter category.
                                                System.Drawing.Imaging.Encoder myEncoder =
                                                    System.Drawing.Imaging.Encoder.Quality;

                                                // Create an EncoderParameters object. 
                                                // An EncoderParameters object has an array of EncoderParameter 
                                                // objects. In this case, there is only one 
                                                // EncoderParameter object in the array.



                                                #region SAVING THE COMPRESS IMAGE FILE
                                                EncoderParameters myEncoderParameters = new EncoderParameters(1);

                                                EncoderParameter myEncoderParameter = new EncoderParameter(myEncoder, 50L);
                                                myEncoderParameters.Param[0] = myEncoderParameter;

                                                bmp1.Save(filesInSubDir + "\\" + "Zip" + GettingImageNameForOptimizedImage(imageFile), jpgEncoder, myEncoderParameters);//pathOfImage
                                                Console.WriteLine(filesInSubDir + GettingImageNameForOptimizedImage(imageFile) + "  CREATED");//pathOfImage 
                                                #endregion

                                                #region DELETING THE ORIGNAL FILE
                                                bmp1.Dispose();
                                                System.IO.File.Delete(filesInSubDir + "\\" + GettingImageNameForOptimizedImage(imageFile));//pathOfImage
                                                Console.WriteLine(imageFile.Replace("jpg", "png") + "  DELETED");//pathOfImage 
                                                #endregion
                                                //myEncoderParameter = new EncoderParameter(myEncoder, 100L);
                                                //myEncoderParameters.Param[0] = myEncoderParameter;
                                                //bmp1.Save("D:\\" + RemovingImageFormat[0] + "100L" + ".jpg", jpgEncoder, myEncoderParameters);

                                                #region BACK RENAMING FILE TO ORIGNAL NAME
                                                System.IO.File.Move(filesInSubDir + "\\" + "Zip" + GettingImageNameForOptimizedImage(imageFile), filesInSubDir + "\\" + GettingImageNameForOptimizedImage(imageFile)); 
                                                #endregion
                                            }
                                            catch (Exception ex)
                                            {
                                                Console.Write("\n" + ex.Message + " Press enter to continue :");
                                                Console.ReadLine();

                                                Console.Write("\nWould you like to retry ? [Y/N] :");
                                                string resp = Console.ReadLine();
                                                if (resp == "Y" || resp == "y")
                                                {
                                                    Console.WriteLine("                 -------------------\n\n");
                                                    Main(null);
                                                }
                                            }
                                        }
                                    }
                                }
                            }
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Console.Write(ex);
                Console.Read();
            }

            Console.Write("Press any key to exit...");
            Console.Read();
            // Get a bitmap. ###################################################################


        }
        private ImageCodecInfo GetEncoder(ImageFormat format)
        {

            ImageCodecInfo[] codecs = ImageCodecInfo.GetImageDecoders();

            foreach (ImageCodecInfo codec in codecs)
            {
                if (codec.FormatID == format.Guid)
                {
                    return codec;
                }
            }
            return null;
        }
        public string GettingImageNameForOptimizedImage(string pathOfImage)
        {
            try
            {
                string[] splitingPathOfImage = pathOfImage.Split('\\');
                string[] RemovingImageFormat = splitingPathOfImage[splitingPathOfImage.Count() - 1].ToString().Split('.');
                return RemovingImageFormat[0] + ".jpg";
            }
            catch (Exception)
            {
                return null;
            }
            return null;
        }
        public static void LoggingOperations(string ImageName, string Status, bool UpdateRequired)
        {
            try
            {
                if (!File.Exists(_StatusLog))
                {
                    using (File.Create(_StatusLog)) { }
                    DirectorySecurity sec = Directory.GetAccessControl(_StatusLog);
                    SecurityIdentifier everyone = new SecurityIdentifier(WellKnownSidType.WorldSid, null);
                    sec.AddAccessRule(new FileSystemAccessRule(everyone, FileSystemRights.Modify | FileSystemRights.Synchronize, InheritanceFlags.ContainerInherit | InheritanceFlags.ObjectInherit, PropagationFlags.None, AccessControlType.Allow));
                    Directory.SetAccessControl(_StatusLog, sec);
                }
                if (UpdateRequired == true)
                {
                    string UpdateStatusText = File.ReadAllText(_StatusLog);
                    UpdateStatusText = UpdateStatusText.Replace(ImageName, ImageName + "," + Status);
                    File.WriteAllText(_StatusLog, UpdateStatusText);
                    UpdateStatusText = "";
                }
                else
                {
                    File.AppendAllText(_StatusLog, Environment.NewLine);
                    File.AppendAllText(_StatusLog, Status);
                }
            }
            catch (Exception)
            {
            }
        }

For PNG compression i changed the following line.

Bitmap bmp1 = new Bitmap(imageFile);//pathOfImage);
ImageCodecInfo jpgEncoder = GetEncoder(ImageFormat.Png);

Kindly some one help me out. If there is a new method, I welcome it. If this could be altered, it would a lot better.

Answer 1

PNG Images are 32 bits by default. You can convert them to 8 bits : resulting file will be about 5 times smaller than the original one. With most images, the loss of quality is almost invisible.

This is what online png compressors do.

You can do this yourself by using nQuant : http://nquant.codeplex.com/ (available on Nuget)

var quantizer = new WuQuantizer();         
using(var quantized = quantizer.QuantizeImage(bmp1))
{
    quantized.Save(targetPath, ImageFormat.Png);
}

Full explanation of the method is available on this blog post http://www.hurryupandwait.io/blog/convert-32-bit-pngs-to-high-quality-8-bit-pngs-with-c