I encountered a little bit of a problem the other day with some image resizing code from within an ASP.NET MVC application that was misbehaving. The issue was just a general C# and ASP.NET one, not related to MVC or Webforms, but it was that for some reason the images were losing a significant amount of quality when resizing. I'm talking a pixel sharp 2000 x 2000 picture that when resized to 300 x 300, was woefully blurry. Initially, the code was simply using the GetThumbnailImage() method to produce it's resizes, this turned out to be the mistake!

While GetThumbnailImage() is fine for small thumbnail images (the clue I guess, was in the name), it somewhat struggled on the larger versions. To fix the issue, I had to convert the image to a bitmap, faff about with it like that, then export it back to a Jpeg once I was done.

For future me (and anyone else this might help), here is the code I eventually settled on:

EncoderParameters encodingParameters = new EncoderParameters(1);
encodingParameters.Param[0] = new EncoderParameter(Encoder.Quality, 90L); // Set the JPG Quality percentage to 90%.
 
ImageCodecInfo jpgEncoder = GetEncoderInfo("image/jpeg");
 
// Incoming! This is the original image. This line can effectively be anything, but in this example it's coming from a stream.
var image = Image.FromStream(new System.IO.MemoryStream(Picture));
 
// Creating two blank canvas. One that the original image is placed into, the other for the resized version.
Bitmap originalImage = new Bitmap(image);
Bitmap newImage = new Bitmap(originalImage, 300, (image.Height * 300 / image.Width));  // Width of 300 & maintain aspect ratio (let it be as high as it needs to be).
 
// We then do some funky voodoo with the newImage. Changing it to a graphic to allow us to set the HighQualityBilinear property and resize nicely.
Graphics g = Graphics.FromImage(newImage);
g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBilinear;
g.DrawImage(originalImage, 0, 0, newImage.Width, newImage.Height);
 
var streamLarge = new System.IO.MemoryStream();
newImage.Save(streamLarge, jpgEncoder, encodingParameters);
 
// This is the line that returns the picture to the relevant part of the model.
_event.Picture = streamLarge.ToArray();
 
// No need for all that drama for the thumbnail, the loss of quality isn't noticable.
var thumbnail = image.GetThumbnailImage(80, (image.Height*80/image.Width), null, new IntPtr(0));
var streamThumbnail = new System.IO.MemoryStream();
 
thumbnail.Save(streamThumbnail, jpgEncoder, encodingParameters);
 _event.ThumbnailPicture = streamThumbnail.ToArray();
 
// Good boy's tidy-up after themselves! :O
originalImage.Dispose();
newImage.Dispose();
thumbnail.Dispose();
streamLarge.Dispose();
streamThumbnail.Dispose();