Resizing an image in asp.net without losing the image quality

Question

I am developing an ASP.NET 3.5 web application in which I am allowing my users to upload either jpeg,gif,bmp or png images. If the uploaded image dimensions are greater then 103 x 32 the I want to resize the uploaded image to 103 x 32. I have read some blog posts and articles, and have also tried some of the code samples but nothing seems to work right. Has anyone succeed in doing this?

Answer 1

I had the same problem a while back and dealt with it this way:

private Image RezizeImage(Image img, int maxWidth, int maxHeight) {     if(img.Height < maxHeight && img.Width < maxWidth) return img;     using (img)     {         Double xRatio = (double)img.Width / maxWidth;         Double yRatio = (double)img.Height / maxHeight;         Double ratio = Math.Max(xRatio, yRatio);         int nnx = (int)Math.Floor(img.Width / ratio);         int nny = (int)Math.Floor(img.Height / ratio);         Bitmap cpy = new Bitmap(nnx, nny, PixelFormat.Format32bppArgb);         using (Graphics gr = Graphics.FromImage(cpy))         {             gr.Clear(Color.Transparent);              // This is said to give best quality when resizing images             gr.InterpolationMode = InterpolationMode.HighQualityBicubic;              gr.DrawImage(img,                 new Rectangle(0, 0, nnx, nny),                 new Rectangle(0, 0, img.Width, img.Height),                 GraphicsUnit.Pixel);         }         return cpy;     }  }  private MemoryStream BytearrayToStream(byte[] arr) {     return new MemoryStream(arr, 0, arr.Length); }  private void HandleImageUpload(byte[] binaryImage) {     Image img = RezizeImage(Image.FromStream(BytearrayToStream(binaryImage)), 103, 32);     img.Save("IMAGELOCATION.png", System.Drawing.Imaging.ImageFormat.Gif); } 

I just read that this was the the way to get highest quality.

Answer 2

This is the code I use. It supports rotation, and also sets the image resolution to the JPEG standards of 72dpi@24-bit color (by default GDI+ saves images at 96dpi@32-bit color). It also fixes the black/gray border problem that some people experience when resizing images.

/// <summary> /// Resizes and rotates an image, keeping the original aspect ratio. Does not dispose the original /// Image instance. /// </summary> /// <param name="image">Image instance</param> /// <param name="width">desired width</param> /// <param name="height">desired height</param> /// <param name="rotateFlipType">desired RotateFlipType</param> /// <returns>new resized/rotated Image instance</returns> public static Image Resize(Image image, int width, int height, RotateFlipType rotateFlipType) {     // clone the Image instance, since we don't want to resize the original Image instance     var rotatedImage = image.Clone() as Image;     rotatedImage.RotateFlip(rotateFlipType);     var newSize = CalculateResizedDimensions(rotatedImage, width, height);      var resizedImage = new Bitmap(newSize.Width, newSize.Height, PixelFormat.Format32bppArgb);     resizedImage.SetResolution(72, 72);      using (var graphics = Graphics.FromImage(resizedImage))     {         // set parameters to create a high-quality thumbnail         graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;         graphics.SmoothingMode = SmoothingMode.AntiAlias;         graphics.CompositingQuality = CompositingQuality.HighQuality;         graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;          // use an image attribute in order to remove the black/gray border around image after resize         // (most obvious on white images), see this post for more information:         // http://www.codeproject.com/KB/GDI-plus/imgresizoutperfgdiplus.aspx         using (var attribute = new ImageAttributes())         {             attribute.SetWrapMode(WrapMode.TileFlipXY);              // draws the resized image to the bitmap             graphics.DrawImage(rotatedImage, new Rectangle(new Point(0, 0), newSize), 0, 0, rotatedImage.Width, rotatedImage.Height, GraphicsUnit.Pixel, attribute);         }     }      return resizedImage; }  /// <summary> /// Calculates resized dimensions for an image, preserving the aspect ratio. /// </summary> /// <param name="image">Image instance</param> /// <param name="desiredWidth">desired width</param> /// <param name="desiredHeight">desired height</param> /// <returns>Size instance with the resized dimensions</returns> private static Size CalculateResizedDimensions(Image image, int desiredWidth, int desiredHeight) {     var widthScale = (double)desiredWidth / image.Width;     var heightScale = (double)desiredHeight / image.Height;      // scale to whichever ratio is smaller, this works for both scaling up and scaling down     var scale = widthScale < heightScale ? widthScale : heightScale;      return new Size                    {                        Width = (int) (scale * image.Width),                        Height = (int) (scale * image.Height)                    }; }