Jon's Blog

.NET Development & More

Using ASP.NET and GDI+ to Resize Uploaded Image

Below is some sample code I used to resize an uploaded image if the image does not meet the required width and height.  MAX_WIDTH and MAX_HEIGHT below are constants.  Change them as needed.  I am saving the resized image as a JPEG.  It is also a good idea to inform the user that their image was resized.  I removed that code to increase readability.

Note: In this sample the image is being saved to a database, but you could also save it to a file if you wanted to.

if (fileUpload.HasFile)
// Get uploaded image from upload control
System.Drawing.Image uploadedImage = System.Drawing.Image.FromStream(fileUpload.PostedFile.InputStream);

// Check width and height of image and resize if necessary
if (uploadedImage.Width > MAX_WIDTH || uploadedImage.Height > MAX_HEIGHT)
// Get the factor we must resize by
decimal heightFactor = Decimal.Divide(uploadedImage.Height, MAX_HEIGHT);
decimal widthFactor = Decimal.Divide(uploadedImage.Width, MAX_WIDTH);
decimal resizeFactor = Math.Max(heightFactor, widthFactor);

// Calculate the new height and width using the resize factor
int newHeight = Convert.ToInt32(uploadedImage.Height / resizeFactor);
int newWidth = Convert.ToInt32(uploadedImage.Width / resizeFactor);

Bitmap sourceBitmap = new Bitmap(uploadedImage);
Bitmap newBitmap = new Bitmap(newWidth, newHeight);
Graphics graphics = Graphics.FromImage(newBitmap);
MemoryStream memoryStream = new MemoryStream();

// Set quality settings and save to MemoryStream object as Jpeg
graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
graphics.CompositingQuality = CompositingQuality.HighQuality;
graphics.SmoothingMode = SmoothingMode.HighQuality;
graphics.DrawImage(sourceBitmap, new Rectangle(0, 0, newWidth, newHeight));
newBitmap.Save(memoryStream, ImageFormat.Jpeg);

// Save to Business Object
bizObject.FileData = new Binary(memoryStream.ToArray());
bizObject.FileType = "image/jpeg";
bizObject.FileName = Path.GetFileNameWithoutExtension(fileUpload.FileName) + ".jpg";
catch (Exception)
// Dispose of graphics objects
// Image size is correct, so save what was uploaded
bizObject.FileType = fileUpload.PostedFile.ContentType;
bizObject.FileName = fileUpload.FileName;
bizObject.FileData = new Binary(fileUpload.FileBytes);

// Other code removed for clarity

File Upload: File Extension Validation

This is an easy way to validate the file extension on a FileUpload control.  This way you won't have to postback to the server to validate.  Unless, of course, the user has JavaScript turned off.  The example below is for images (JPEG, GIF, or PNG).

<asp:RegularExpressionValidator ID="regxImage" runat="server" Text="*" 
="Image must be a JPEG, GIF, or PNG."
ControlToValidate="myFileUpload" />