Esse método reduz a imagem sem perder a qualidade:
public void ResizeImage(double scaleFactor, Stream fromStream, Stream toStream)
{
var image = Image.FromStream(fromStream);
var newWidth = (int)(image.Width * scaleFactor);
var newHeight = (int)(image.Height * scaleFactor);
var thumbnailBitmap = new Bitmap(newWidth, newHeight);
var thumbnailGraph = Graphics.FromImage(thumbnailBitmap);
thumbnailGraph.CompositingQuality = CompositingQuality.HighQuality;
thumbnailGraph.SmoothingMode = SmoothingMode.HighQuality;
thumbnailGraph.InterpolationMode = InterpolationMode.HighQualityBicubic;
var imageRectangle = new Rectangle(0, 0, newWidth, newHeight);
thumbnailGraph.DrawImage(image, imageRectangle);
thumbnailBitmap.Save(toStream, image.RawFormat);
thumbnailGraph.Dispose();
thumbnailBitmap.Dispose();
image.Dispose();
}
Fonte: http://weblogs.asp.net/gunnarpeipman/archive/2009/04/02/resizing-images-without-loss-of-quality.aspx
João Paulo Gomes http://johnowl.com/
