C#不改变图像长宽比例调整图像大小方式

/// <summary>
/// 根据容器（如PictureBox）长宽的限制，在不改变图像比例的情况下，调整图像大小
/// author:huangyq1984@qq.com
/// </summary>
/// <param name="maxWidth">容器宽</param>
/// <param name="maxHeight">容器高</param>
/// <param name="srcImg">原图</param>
/// <param name="backColor">空白处的背景色</param>
/// <returns></returns>
public static Image GetImageToFitContainer(int maxWidth,int maxHeight, Image srcImg, Color backColor)
{
    if (srcImg == null) return null;
    float Scale;
    int iw, ih;
    //计算原图的长宽比例
    Scale = (float)srcImg.Height / (float)srcImg.Width;
    iw = srcImg.Width;
    ih = srcImg.Height;
    //如果原图长宽都不大于容器长和宽，则不需要调整大小
    if (srcImg.Width <= maxWidth && srcImg.Height <= maxHeight)
    {
        iw = srcImg.Width;
        ih = srcImg.Height;
    }
    //如果原图宽大于容器宽，且原图高不大于容器高，则调整后的图像宽就是容器宽，图像高需要根据长宽比例来计算
    else if (srcImg.Width > maxWidth && srcImg.Height <= maxHeight)
    {
        iw = maxWidth;
        ih = (int)(Scale * iw);
    }
    //如果原图高大于容器高，且原图宽不大于容器宽，则调整后的图像高就是容器高，图像宽需要根据长宽比例来计算
    else if (srcImg.Width <= maxWidth && srcImg.Height > maxHeight)
    {
        ih = maxHeight;
        iw = (int)(ih / Scale);
    }
    //如果原图高和宽都大于容器高和宽，则调整后的图像高和图像宽都需要重新计算
    else if (srcImg.Width > maxWidth && srcImg.Height > maxHeight)
    {
        iw = maxWidth;
        ih = (int)(Scale * iw);
        if (ih > maxHeight)
        {
            ih = maxHeight;
            iw = (int)(ih / Scale);
        }
    }
    //构建新的位图
    Bitmap bmp = new Bitmap(iw, ih);
    Graphics g = Graphics.FromImage(bmp);
    //用背景色填充
    g.Clear(backColor);
    //在位图上根据调整后的高和宽绘制原图
    g.DrawImage(srcImg, 0, 0, iw, ih);
    //保存
    System.IO.MemoryStream ms = new System.IO.MemoryStream();
    bmp.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
    g.Dispose();

    srcImg = (Image)bmp;
    return srcImg;
}

Image srcImage = Image.FromFile(fileName);
pictureBox1.SizeMode = PictureBoxSizeMode.CenterImage;
pictureBox1.Image = GetImageToFitContainer(pictureBox1.Width,pictureBox1.Height,srcImage,Color.Transparent);