/// <summary>
/// 获取一个图片按等比例缩小后的大小。
/// </summary>
/// <param name="maxWidth">需要缩小到的宽度</param>
/// <param name="maxHeight">需要缩小到的高度</param>
/// <param name="imageOriginalWidth">图片的原始宽度</param>
/// <param name="imageOriginalHeight">图片的原始高度</param>
/// <returns>返回图片按等比例缩小后的实际大小</returns>
public static Size GetNewSize(int maxWidth, int maxHeight, int imageOriginalWidth, int imageOriginalHeight)
{
    double w = 0.0;
    double h = 0.0;
    double sw = Convert.ToDouble(imageOriginalWidth);
    double sh = Convert.ToDouble(imageOriginalHeight);
    double mw = Convert.ToDouble(maxWidth);
    double mh = Convert.ToDouble(maxHeight);

    if (sw < mw && sh < mh)
    {
        w = sw;
        h = sh;
    }
    else if ((sw / sh) > (mw / mh))
    {
        w = maxWidth;
        h = (w * sh) / sw;
    }
    else
    {
        h = maxHeight;
        w = (h * sw) / sh;
    }

    return new Size(Convert.ToInt32(w), Convert.ToInt32(h));
}

/// <summary>
/// 对给定的一个图片（Image对象）生成一个指定大小的缩略图。
/// </summary>
/// <param name="originalImage">原始图片</param>
/// <param name="thumMaxWidth">缩略图的宽度</param>
/// <param name="thumMaxHeight">缩略图的高度</param>
/// <returns>返回缩略图的Image对象</returns>
public static System.Drawing.Image GetThumbNailImage(System.Drawing.Image originalImage, int thumMaxWidth, int thumMaxHeight)
{
    Size thumRealSize = Size.Empty;
    System.Drawing.Image newImage = originalImage;
    Graphics graphics = null;

    try
    {
        thumRealSize = GetNewSize(thumMaxWidth, thumMaxHeight, originalImage.Width, originalImage.Height);
        newImage = new Bitmap(thumRealSize.Width, thumRealSize.Height);
        graphics = Graphics.FromImage(newImage);

        graphics.CompositingQuality = CompositingQuality.HighQuality;
        graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
        graphics.SmoothingMode = SmoothingMode.HighQuality;

        graphics.Clear(Color.Transparent);

        graphics.DrawImage(originalImage, new Rectangle(0, 0, thumRealSize.Width, thumRealSize.Height), new Rectangle(0, 0, originalImage.Width, originalImage.Height), GraphicsUnit.Pixel);
    }
    catch { }
    finally
    {
        if (graphics != null)
        {
            graphics.Dispose();
            graphics = null;
        }
    }

    return newImage;
}
/// <summary>
/// 对给定的一个图片文件生成一个指定大小的缩略图。
/// </summary>
/// <param name="originalImage">图片的物理文件地址</param>
/// <param name="thumMaxWidth">缩略图的宽度</param>
/// <param name="thumMaxHeight">缩略图的高度</param>
/// <returns>返回缩略图的Image对象</returns>
public static System.Drawing.Image GetThumbNailImage(string imageFile, int thumMaxWidth, int thumMaxHeight)
{
    System.Drawing.Image originalImage = null;
    System.Drawing.Image newImage = null;

    try
    {
        originalImage = System.Drawing.Image.FromFile(imageFile);
        newImage = GetThumbNailImage(originalImage, thumMaxWidth, thumMaxHeight);
    }
    catch { }
    finally
    {
        if (originalImage != null)
        {
            originalImage.Dispose();
            originalImage = null;
        }
    }

    return newImage;
}
/// <summary>
/// 对给定的一个图片文件生成一个指定大小的缩略图，并将缩略图保存到指定位置。
/// </summary>
/// <param name="originalImageFile">图片的物理文件地址</param>
/// <param name="thumbNailImageFile">缩略图的物理文件地址</param>
/// <param name="thumMaxWidth">缩略图的宽度</param>
/// <param name="thumMaxHeight">缩略图的高度</param>
public static void MakeThumbNail(string originalImageFile, string thumbNailImageFile, int thumMaxWidth, int thumMaxHeight)
{
    System.Drawing.Image newImage = GetThumbNailImage(originalImageFile, thumMaxWidth, thumMaxHeight);
    try
    {
        newImage.Save(thumbNailImageFile, ImageFormat.Jpeg);
    }
    catch
    { }
    finally
    {
        newImage.Dispose();
        newImage = null;
    }
}
/// <summary>
/// 将一个图片的内存流调整为指定大小，并返回调整后的内存流。
/// </summary>
/// <param name="originalImageStream">原始图片的内存流</param>
/// <param name="newWidth">新图片的宽度</param>
/// <param name="newHeight">新图片的高度</param>
/// <returns>返回调整后的图片的内存流</returns>
public static MemoryStream ResizeImage(Stream originalImageStream, int newWidth, int newHeight)
{
    MemoryStream newImageStream = null;

    System.Drawing.Image newImage = Globals.GetThumbNailImage(System.Drawing.Image.FromStream(originalImageStream), newWidth, newHeight);
    if (newImage != null)
    {
        newImageStream = new MemoryStream();
        newImage.Save(newImageStream, ImageFormat.Jpeg);
    }

    return newImageStream;
}
/// <summary>
/// 将一个内存流保存为磁盘文件。
/// </summary>
/// <param name="stream">内存流</param>
/// <param name="newFile">目标磁盘文件地址</param>
public static void SaveStreamToFile(Stream stream, string newFile)
{
    if (stream == null || stream.Length == 0 || string.IsNullOrEmpty(newFile))
    {
        return;
    }

    byte[] buffer = new byte[stream.Length];
    stream.Position = 0;
    stream.Read(buffer, 0, buffer.Length);
    FileStream fileStream = new FileStream(newFile, FileMode.OpenOrCreate, FileAccess.Write);
    fileStream.Write(buffer, 0, buffer.Length);
    fileStream.Flush();
    fileStream.Close();
    fileStream.Dispose();
}
/// <summary>
/// 对一个指定的图片加上图片水印效果。
/// </summary>
/// <param name="imageFile">图片文件地址</param>
/// <param name="waterImage">水印图片（Image对象）</param>
public static void CreateImageWaterMark(string imageFile, System.Drawing.Image waterImage)
{
    if (string.IsNullOrEmpty(imageFile) || !File.Exists(imageFile) || waterImage == null)
    {
        return;
    }

    System.Drawing.Image originalImage = System.Drawing.Image.FromFile(imageFile);

    if (originalImage.Width - 10 < waterImage.Width || originalImage.Height - 10 < waterImage.Height)
    {
        return;
    }

    Graphics graphics = Graphics.FromImage(originalImage);

    int x = originalImage.Width - waterImage.Width - 10;
    int y = originalImage.Height - waterImage.Height - 10;
    int width = waterImage.Width;
    int height = waterImage.Height;

    graphics.DrawImage(waterImage, new Rectangle(x, y, width, height), 0, 0, width, height, GraphicsUnit.Pixel);
    graphics.Dispose();

    MemoryStream stream = new MemoryStream();
    originalImage.Save(stream, ImageFormat.Jpeg);
    originalImage.Dispose();

    System.Drawing.Image imageWithWater = System.Drawing.Image.FromStream(stream);

    imageWithWater.Save(imageFile);
    imageWithWater.Dispose();
}
/// <summary>
/// 对一个指定的图片加上文字水印效果。
/// </summary>
/// <param name="imageFile">图片文件地址</param>
/// <param name="waterText">水印文字内容</param>
public static void CreateTextWaterMark(string imageFile, string waterText)
{
    if (string.IsNullOrEmpty(imageFile) || string.IsNullOrEmpty(waterText) || !File.Exists(imageFile))
    {
        return;
    }

    System.Drawing.Image originalImage = System.Drawing.Image.FromFile(imageFile);

    Graphics graphics = Graphics.FromImage(originalImage);

    graphics.SmoothingMode = SmoothingMode.HighQuality;
    graphics.TextRenderingHint = TextRenderingHint.ClearTypeGridFit;
    graphics.CompositingQuality = CompositingQuality.HighQuality;
    graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;

    SolidBrush brush = new SolidBrush(Color.FromArgb(153, 255, 255, 255));
    Font waterTextFont = new Font("Arial", 16, FontStyle.Regular);
    SizeF waterTextSize = graphics.MeasureString(waterText, waterTextFont);

    float x = (float)originalImage.Width - waterTextSize.Width - 10F;
    float y = (float)originalImage.Height - waterTextSize.Height - 10F;

    graphics.DrawString(waterText, waterTextFont, brush, x, y);

    graphics.Dispose();
    brush.Dispose();

    MemoryStream stream = new MemoryStream();
    originalImage.Save(stream, ImageFormat.Jpeg);
    originalImage.Dispose();

    System.Drawing.Image imageWithWater = System.Drawing.Image.FromStream(stream);

    imageWithWater.Save(imageFile);
    imageWithWater.Dispose();
}

/// <summary>
/// 判断上传组件是否包含内容。
/// </summary>
/// <param name="fileUpload">ASP.NET 2.0标准上传组件</param>
/// <returns>如果数据有效，则返回True，否则返回False</returns>
public static bool IsAttachmentValid(FileUpload fileUpload)
{
    if (fileUpload != null &&
        fileUpload.PostedFile != null &&
        !string.IsNullOrEmpty(fileUpload.PostedFile.FileName) &&
        fileUpload.PostedFile.ContentLength > 0)
    {
        return true;
    }
    return false;
}