Question

I want to scale an image in C# with quality level as good as Photoshop does. Is there any C# image processing library available to do this thing?

Answer 1

Here’s a nicely commented Image Manipulation helper class that you can look at and use. I wrote it as an example of how to perform certain image manipulation tasks in C#. You’ll be interested in the ResizeImage function that takes a System.Drawing.Image, the width and the height as the arguments.

using System; using System.Collections.Generic; using System.Drawing; using System.Drawing.Imaging;  namespace DoctaJonez.Drawing.Imaging {     /// <summary>     /// Provides various image untilities, such as high quality resizing and the ability to save a JPEG.     /// </summary>     public static class ImageUtilities     {             /// <summary>         /// A quick lookup for getting image encoders         /// </summary>         private static Dictionary<string, ImageCodecInfo> encoders = null;          /// <summary>         /// A lock to prevent concurrency issues loading the encoders.         /// </summary>         private static object encodersLock = new object();          /// <summary>         /// A quick lookup for getting image encoders         /// </summary>         public static Dictionary<string, ImageCodecInfo> Encoders         {             //get accessor that creates the dictionary on demand             get             {                 //if the quick lookup isn't initialised, initialise it                 if (encoders == null)                 {                     //protect against concurrency issues                     lock (encodersLock)                     {                         //check again, we might not have been the first person to acquire the lock (see the double checked lock pattern)                         if (encoders == null)                         {                             encoders = new Dictionary<string, ImageCodecInfo>();                              //get all the codecs                             foreach (ImageCodecInfo codec in ImageCodecInfo.GetImageEncoders())                             {                                 //add each codec to the quick lookup                                 encoders.Add(codec.MimeType.ToLower(), codec);                             }                         }                     }                 }                  //return the lookup                 return encoders;             }         }          /// <summary>         /// Resize the image to the specified width and height.         /// </summary>         /// <param name='image'>The image to resize.</param>         /// <param name='width'>The width to resize to.</param>         /// <param name='height'>The height to resize to.</param>         /// <returns>The resized image.</returns>         public static System.Drawing.Bitmap ResizeImage(System.Drawing.Image image, int width, int height)         {             //a holder for the result             Bitmap result = new Bitmap(width, height);             //set the resolutions the same to avoid cropping due to resolution differences             result.SetResolution(image.HorizontalResolution, image.VerticalResolution);              //use a graphics object to draw the resized image into the bitmap             using (Graphics graphics = Graphics.FromImage(result))             {                 //set the resize quality modes to high quality                 graphics.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;                 graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;                 graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;                 //draw the image into the target bitmap                 graphics.DrawImage(image, 0, 0, result.Width, result.Height);             }              //return the resulting bitmap             return result;         }          /// <summary>          /// Saves an image as a jpeg image, with the given quality          /// </summary>          /// <param name='path'>Path to which the image would be saved.</param>          /// <param name='quality'>An integer from 0 to 100, with 100 being the          /// highest quality</param>          /// <exception cref='ArgumentOutOfRangeException'>         /// An invalid value was entered for image quality.         /// </exception>         public static void SaveJpeg(string path, Image image, int quality)         {             //ensure the quality is within the correct range             if ((quality < 0) || (quality > 100))             {                 //create the error message                 string error = string.Format('Jpeg image quality must be between 0 and 100, with 100 being the highest quality.  A value of {0} was specified.', quality);                 //throw a helpful exception                 throw new ArgumentOutOfRangeException(error);             }              //create an encoder parameter for the image quality             EncoderParameter qualityParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);             //get the jpeg codec             ImageCodecInfo jpegCodec = GetEncoderInfo('image/jpeg');              //create a collection of all parameters that we will pass to the encoder             EncoderParameters encoderParams = new EncoderParameters(1);             //set the quality parameter for the codec             encoderParams.Param[0] = qualityParam;             //save the image using the codec and the parameters             image.Save(path, jpegCodec, encoderParams);         }          /// <summary>          /// Returns the image codec with the given mime type          /// </summary>          public static ImageCodecInfo GetEncoderInfo(string mimeType)         {             //do a case insensitive search for the mime type             string lookupKey = mimeType.ToLower();              //the codec to return, default to null             ImageCodecInfo foundCodec = null;              //if we have the encoder, get it to return             if (Encoders.ContainsKey(lookupKey))             {                 //pull the codec from the lookup                 foundCodec = Encoders[lookupKey];             }              return foundCodec;         }      } } 

---

Update

A few people have been asking in the comments for samples of how to consume the ImageUtilities class, so here you go.

//resize the image to the specified height and width using (var resized = ImageUtilities.ResizeImage(image, 50, 100)) {     //save the resized image as a jpeg with a quality of 90     ImageUtilities.SaveJpeg(@'C:\myimage.jpeg', resized, 90); } 

Note

Remember that images are disposable, so you need to assign the result of your resize to a using declaration (or you could use a try finally and make sure you call dispose in your finally).