等比例缩放图片（C#）

       在使用图片的过程中，我们有时候需要将图片缩放到特定的宽度和高度，但是又不希望图片被直接拉伸而变形，而是实现图片的等比例缩放。类似于Winform的PictureBox的SizeMode属性的Zoom，而不是StretchImage。

//等比例缩放图片
private Bitmap ZoomImage(Bitmap bitmap, int destHeight, int destWidth)
{
    try
    {
        System.Drawing.Image sourImage = bitmap;
        int width = 0, height = 0;
        //按比例缩放           
        int sourWidth = sourImage.Width;
        int sourHeight = sourImage.Height;
        if (sourHeight > destHeight || sourWidth > destWidth)
        {
            if ((sourWidth * destHeight) > (sourHeight * destWidth))
            {
                width = destWidth;
                height = (destWidth * sourHeight) / sourWidth;
            }
            else
            {
                height = destHeight;
                width = (sourWidth * destHeight) / sourHeight;
            }
        }
        else
        {
            width = sourWidth;
            height = sourHeight;
        }
        Bitmap destBitmap = new Bitmap(destWidth, destHeight);
        Graphics g = Graphics.FromImage(destBitmap);
        g.Clear(Color.Transparent);
        //设置画布的描绘质量         
        g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
        g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
        g.DrawImage(sourImage, new Rectangle((destWidth - width) / 2, (destHeight - height) / 2, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);
        g.Dispose();
        //设置压缩质量     
        System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();
        long[] quality = new long[1];
        quality[0] = 100;
        System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
        encoderParams.Param[0] = encoderParam;
        sourImage.Dispose();
        return destBitmap;
    }
    catch
    {
        return bitmap;
    }
}