学步园

    public static byte[] ResizeImageFile(byte[] imageFile, PhotoSize size)
        {
            using (System.Drawing.Image original = System.Drawing.Image.FromStream(new MemoryStream(imageFile)))
            {
                int targetH, targetW;
                if (size == PhotoSize.Small || size == PhotoSize.Medium)
                {
                    // regardless of orientation,
                    // the *height* is constant for thumbnail images (UI constraint)

                    if (original.Height > original.Width)
                    {
                        if (size == PhotoSize.Small)
                            targetH = DefaultValues.FixedSmallImageHeight;
                        else
                            targetH = DefaultValues.FixedMediumImageHeight;

                        targetW = (int)(original.Width * ((float)targetH / (float)original.Height));
                    }
                    else
                    {
                        if (size == PhotoSize.Small)
                            targetW = DefaultValues.FixedSmallImageWidth;
                        else
                            targetW = DefaultValues.FixedMediumImageWidth;

                        targetH = (int)(original.Height * ((float)targetW / (float)original.Width));
                    }
                }
                else
                {
                    // for full preview, we scale proportionally according to orienation
                    if (original.Height > original.Width)
                    {
                        targetH = Math.Min(original.Height, DefaultValues.MaxFullImageSize);
                        targetW = (int)(original.Width * ((float)targetH / (float)original.Height));
                    }
                    else
                    {
                        targetW = Math.Min(original.Width, DefaultValues.MaxFullImageSize);
                        targetH = (int)(original.Height * ((float)targetW / (float)original.Width));
                    }
                }

                using (System.Drawing.Image imgPhoto = System.Drawing.Image.FromStream(new MemoryStream(imageFile)))
                {
                    // Create a new blank canvas.  The resized image will be drawn on this canvas.
                    using (Bitmap bmPhoto = new Bitmap(targetW, targetH, PixelFormat.Format24bppRgb))
                    {
                        bmPhoto.SetResolution(72, 72);

                        using (Graphics grPhoto = Graphics.FromImage(bmPhoto))
                        {
                            grPhoto.SmoothingMode = SmoothingMode.AntiAlias;
                            grPhoto.InterpolationMode = InterpolationMode.HighQualityBicubic;
                            grPhoto.PixelOffsetMode = PixelOffsetMode.HighQuality;
                            grPhoto.DrawImage(imgPhoto, new Rectangle(0, 0, targetW, targetH), 0, 0, original.Width, original.Height, GraphicsUnit.Pixel);

                            MemoryStream mm = new MemoryStream();
                            bmPhoto.Save(mm, System.Drawing.Imaging.ImageFormat.Jpeg);
                            return mm.GetBuffer();
                        }
                    }
                }
            }
        }