Here is a complete example of creating a smaller image (thumbnail). This fragment resizes the image, rotates it as necessary (if the phone is held vertically) and creates an image if you want to create square fingers. This snippet creates JPEG, but it can be easily changed for other types of files. Even if the image is smaller than the maximum allowed size, the image will still be compressed and its resolution changed to create images with the same resolution and compression level.
using System; using System.Drawing; using System.Drawing.Drawing2D; using System.Drawing.Imaging; using System.IO; //set the resolution, 72 is usually good enough for displaying images on monitors float imageResolution = 72; //set the compression level. higher compression = better quality = bigger images long compressionLevel = 80L; public Image resizeImage(Image image, int maxWidth, int maxHeight, bool padImage) { int newWidth; int newHeight; //first we check if the image needs rotating (eg phone held vertical when taking a picture for example) foreach (var prop in image.PropertyItems) { if (prop.Id == 0x0112) { int orientationValue = image.GetPropertyItem(prop.Id).Value[0]; RotateFlipType rotateFlipType = getRotateFlipType(orientationValue); image.RotateFlip(rotateFlipType); break; } } //apply the padding to make a square image if (padImage == true) { image = applyPaddingToImage(image, Color.Red); } //check if the with or height of the image exceeds the maximum specified, if so calculate the new dimensions if (image.Width > maxWidth || image.Height > maxHeight) { double ratioX = (double)maxWidth / image.Width; double ratioY = (double)maxHeight / image.Height; double ratio = Math.Min(ratioX, ratioY); newWidth = (int)(image.Width * ratio); newHeight = (int)(image.Height * ratio); } else { newWidth = image.Width; newHeight = image.Height; } //start the resize with a new image Bitmap newImage = new Bitmap(newWidth, newHeight); //set the new resolution newImage.SetResolution(imageResolution, imageResolution); //start the resizing using (var graphics = Graphics.FromImage(newImage)) { //set some encoding specs graphics.CompositingMode = CompositingMode.SourceCopy; graphics.CompositingQuality = CompositingQuality.HighQuality; graphics.SmoothingMode = SmoothingMode.HighQuality; graphics.InterpolationMode = InterpolationMode.HighQualityBicubic; graphics.PixelOffsetMode = PixelOffsetMode.HighQuality; graphics.DrawImage(image, 0, 0, newWidth, newHeight); } //save the image to a memorystream to apply the compression level using (MemoryStream ms = new MemoryStream()) { EncoderParameters encoderParameters = new EncoderParameters(1); encoderParameters.Param[0] = new EncoderParameter(Encoder.Quality, compressionLevel); newImage.Save(ms, getEncoderInfo("image/jpeg"), encoderParameters); //save the image as byte array here if you want the return type to be a Byte Array instead of Image //byte[] imageAsByteArray = ms.ToArray(); } //return the image return newImage; } //=== image padding public Image applyPaddingToImage(Image image, Color backColor) { //get the maximum size of the image dimensions int maxSize = Math.Max(image.Height, image.Width); Size squareSize = new Size(maxSize, maxSize); //create a new square image Bitmap squareImage = new Bitmap(squareSize.Width, squareSize.Height); using (Graphics graphics = Graphics.FromImage(squareImage)) { //fill the new square with a color graphics.FillRectangle(new SolidBrush(backColor), 0, 0, squareSize.Width, squareSize.Height); //put the original image on top of the new square graphics.DrawImage(image, (squareSize.Width / 2) - (image.Width / 2), (squareSize.Height / 2) - (image.Height / 2), image.Width, image.Height); } //return the image return squareImage; } //=== get encoder info private ImageCodecInfo getEncoderInfo(string mimeType) { ImageCodecInfo[] encoders = ImageCodecInfo.GetImageEncoders(); for (int j = 0; j < encoders.Length; ++j) { if (encoders[j].MimeType.ToLower() == mimeType.ToLower()) { return encoders[j]; } } return null; } //=== determine image rotation private RotateFlipType getRotateFlipType(int rotateValue) { RotateFlipType flipType = RotateFlipType.RotateNoneFlipNone; switch (rotateValue) { case 1: flipType = RotateFlipType.RotateNoneFlipNone; break; case 2: flipType = RotateFlipType.RotateNoneFlipX; break; case 3: flipType = RotateFlipType.Rotate180FlipNone; break; case 4: flipType = RotateFlipType.Rotate180FlipX; break; case 5: flipType = RotateFlipType.Rotate90FlipX; break; case 6: flipType = RotateFlipType.Rotate90FlipNone; break; case 7: flipType = RotateFlipType.Rotate270FlipX; break; case 8: flipType = RotateFlipType.Rotate270FlipNone; break; default: flipType = RotateFlipType.RotateNoneFlipNone; break; } return flipType; } //== convert image to base64 public string convertImageToBase64(Image image) { using (MemoryStream ms = new MemoryStream()) { //convert the image to byte array image.Save(ms, ImageFormat.Jpeg); byte[] bin = ms.ToArray(); //convert byte array to base64 string return Convert.ToBase64String(bin); } }
For asp.net users, a small example of how to upload a file, resize it and display the result on the page.
//== the button click method protected void Button1_Click(object sender, EventArgs e) { //check if there is an actual file being uploaded if (FileUpload1.HasFile == false) { return; } using (Bitmap bitmap = new Bitmap(FileUpload1.PostedFile.InputStream)) { try { //start the resize Image image = resizeImage(bitmap, 256, 256, true); //to visualize the result, display as base64 image Label1.Text = "<img src=\"data:image/jpg;base64," + convertImageToBase64(image) + "\">"; //save your image to file sytem, database etc here } catch (Exception ex) { Label1.Text = "Oops! There was an error when resizing the Image.<br>Error: " + ex.Message; } } }