做一个按比例压缩图像的方法

此方法为网上抄袭而来，并非本人原创。

public static void ResizeImageFile(string pathFilename, byte[] imageFile, int targetSize)
    ...{
        using (System.Drawing.Image oldImage = System.Drawing.Image.FromStream(new MemoryStream(imageFile)))
        ...{
            Size newSize = CalculateDimensions(oldImage.Size, targetSize);
            using (Bitmap newImage = new Bitmap(newSize.Width, newSize.Height, PixelFormat.Format24bppRgb))
            ...{
                using (Graphics canvas = Graphics.FromImage(newImage))
                ...{
                    canvas.SmoothingMode = SmoothingMode.AntiAlias;
                    canvas.InterpolationMode = InterpolationMode.HighQualityBicubic;
                    canvas.PixelOffsetMode = PixelOffsetMode.HighQuality;

                    canvas.DrawImage(oldImage, new Rectangle(new Point(0, 0), newSize));

                    if (newSize.Width >= 400)
                    ...{
                        canvas.TextRenderingHint = TextRenderingHint.AntiAlias;
                        string imageCopyright = ConfigurationManager.AppSettings["ImageCopyright"].ToString();
                        Font font = new Font("Verdana", 10);
                        SolidBrush solidBrushBlack = new SolidBrush(Color.Black);
                        SolidBrush solidBrushWhite = new SolidBrush(Color.White);
                        //左上角
                        canvas.DrawString(imageCopyright, font, solidBrushBlack, 5, 5);
                        canvas.DrawString(imageCopyright, font, solidBrushWhite, 6, 6);
                        //右下角
                        SizeF sizeF = new SizeF();
                        sizeF = canvas.MeasureString(imageCopyright, font);
                        canvas.DrawString(imageCopyright, font, solidBrushWhite, newSize.Width - sizeF.Width - 5, newSize.Height - sizeF.Height);
                        canvas.DrawString(imageCopyright, font, solidBrushBlack, newSize.Width - sizeF.Width - 6, newSize.Height - sizeF.Height);
                    }

                    newImage.Save(pathFilename, ImageFormat.Jpeg);
                }
            }
        }
    }

    private static Size CalculateDimensions(Size oldSize, int targetSize)
    ...{
        Size newSize = new Size();
        if (oldSize.Height > oldSize.Width)
        ...{
            if (oldSize.Height < targetSize)
            ...{
                newSize.Width = oldSize.Width;
                newSize.Height = oldSize.Height;
            }
            else
            ...{
                newSize.Width = (int)(oldSize.Width * ((float)targetSize / (float)oldSize.Height) * 0.75);
                newSize.Height = (int)(targetSize * 0.75);
            }
        }
        else
        ...{
            if (oldSize.Width < targetSize)
            ...{
                newSize.Width = oldSize.Width;
                newSize.Height = oldSize.Height;
            }
            else
            ...{
                newSize.Width = targetSize;
                newSize.Height = (int)(oldSize.Height * ((float)targetSize / (float)oldSize.Width));
            }
        }
        return newSize;
    }