Usando C #, ¿cómo puedo cambiar el tamaño de una imagen jpeg?

Usando C #, ¿cómo puedo cambiar el tamaño de una imagen jpeg? Un ejemplo de código sería genial.

public static class ImageHelper { ///  /// Resize the image to the specified width and height. ///  /// The image to resize. /// The width to resize to. /// The height to resize to. /// The resized image. public static Bitmap ResizeImage(Image image, int width, int height) { var destRect = new Rectangle(0, 0, width, height); var destImage = new Bitmap(width, height); destImage.SetResolution(image.HorizontalResolution, image.VerticalResolution); using (var graphics = Graphics.FromImage(destImage)) { graphics.CompositingMode = CompositingMode.SourceCopy; graphics.CompositingQuality = CompositingQuality.HighQuality; graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; graphics.SmoothingMode = SmoothingMode.HighQuality; graphics.PixelOffsetMode = PixelOffsetMode.HighQuality; using (var wrapMode = new ImageAttributes()) { wrapMode.SetWrapMode(WrapMode.TileFlipXY); graphics.DrawImage(image, destRect, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, wrapMode); } } return destImage; } public static Bitmap ResizeImage(Image image, decimal percentage) { int width = (int)Math.Round(image.Width * percentage, MidpointRounding.AwayFromZero); int height = (int)Math.Round(image.Height * percentage, MidpointRounding.AwayFromZero); return ResizeImage(image, width, height); } } class Program { static void Main(string[] args) { string fileName = @"C:\Images\MyImage.jpg"; FileInfo info = new FileInfo(fileName); using (Image image = Image.FromFile(fileName)) { using(Bitmap resizedImage = ImageHelper.ResizeImage(image, 0.25m)) { resizedImage.Save( info.DirectoryName + "\\" + info.Name.Substring(0, info.Name.LastIndexOf(info.Extension)) + "_" + resizedImage.Width + "_" + resizedImage.Height + info.Extension, ImageFormat.Jpeg); } } } } 

C # (o más bien: el .NET framework) en sí no ofrece tal capacidad, pero sí le ofrece Bitmap desde System.Drawing para acceder fácilmente a los datos de píxeles sin formato de varios formatos de imagen. Para el rest, consulte http://en.wikipedia.org/wiki/Image_scaling

Buen filtro de tamaño libre y código de ejemplo.

http://code.google.com/p/zrlabs-yael/

  private void MakeResizedImage(string fromFile, string toFile, int maxWidth, int maxHeight) { int width; int height; using (System.Drawing.Image image = System.Drawing.Image.FromFile(fromFile)) { DetermineResizeRatio(maxWidth, maxHeight, image.Width, image.Height, out width, out height); using (System.Drawing.Image thumbnailImage = image.GetThumbnailImage(width, height, new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero)) { if (image.Width < thumbnailImage.Width && image.Height < thumbnailImage.Height) File.Copy(fromFile, toFile); else { ImageCodecInfo ec = GetCodecInfo(); EncoderParameters parms = new EncoderParameters(1); parms.Param[0] = new EncoderParameter(Encoder.Compression, 40); ZRLabs.Yael.BasicFilters.ResizeFilter rf = new ZRLabs.Yael.BasicFilters.ResizeFilter(); //rf.KeepAspectRatio = true; rf.Height = height; rf.Width = width; System.Drawing.Image img = rf.ExecuteFilter(System.Drawing.Image.FromFile(fromFile)); img.Save(toFile, ec, parms); } } } } 

Estoy usando esto:

  public static void ResizeJpg(string path, int nWidth, int nHeight) { using (var result = new Bitmap(nWidth, nHeight)) { using (var input = new Bitmap(path)) { using (Graphics g = Graphics.FromImage((System.Drawing.Image)result)) { g.DrawImage(input, 0, 0, nWidth, nHeight); } } var ici = ImageCodecInfo.GetImageEncoders().FirstOrDefault(ie => ie.MimeType == "image/jpeg"); var eps = new EncoderParameters(1); eps.Param[0] = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, 100L); result.Save(path, ici, eps); } } 

Buen ejemplo

 public static Image ResizeImage(Image sourceImage, int maxWidth, int maxHeight) { // Determine which ratio is greater, the width or height, and use // this to calculate the new width and height. Effectually constrains // the proportions of the resized image to the proportions of the original. double xRatio = (double)sourceImage.Width / maxWidth; double yRatio = (double)sourceImage.Height / maxHeight; double ratioToResizeImage = Math.Max(xRatio, yRatio); int newWidth = (int)Math.Floor(sourceImage.Width / ratioToResizeImage); int newHeight = (int)Math.Floor(sourceImage.Height / ratioToResizeImage); // Create new image canvas -- use maxWidth and maxHeight in this function call if you wish // to set the exact dimensions of the output image. Bitmap newImage = new Bitmap(newWidth, newHeight, PixelFormat.Format32bppArgb); // Render the new image, using a graphic object using (Graphics newGraphic = Graphics.FromImage(newImage)) { using (var wrapMode = new ImageAttributes()) { wrapMode.SetWrapMode(WrapMode.TileFlipXY); newGraphic.DrawImage(image, destRect, 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, wrapMode); } // Set the background color to be transparent (can change this to any color) newGraphic.Clear(Color.Transparent); // Set the method of scaling to use -- HighQualityBicubic is said to have the best quality newGraphic.InterpolationMode = InterpolationMode.HighQualityBicubic; // Apply the transformation onto the new graphic Rectangle sourceDimensions = new Rectangle(0, 0, sourceImage.Width, sourceImage.Height); Rectangle destinationDimensions = new Rectangle(0, 0, newWidth, newHeight); newGraphic.DrawImage(sourceImage, destinationDimensions, sourceDimensions, GraphicsUnit.Pixel); } // Image has been modified by all the references to it's related graphic above. Return changes. return newImage; } 

Fuente: http://mattmeisinger.com/resize-image-c-sharp