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。

1.  
   //等比例缩放图片
2.  
   private Bitmap ZoomImage(Bitmap bitmap, int destHeight, int destWidth)
3.  
   {
4.  
   try
5.  
   {
6.  
   System.Drawing.Image sourImage = bitmap;
7.  
   int width = 0, height = 0;
8.  
   //按比例缩放
9.  
   int sourWidth = sourImage.Width;
10.  
    int sourHeight = sourImage.Height;
11.  
    if (sourHeight > destHeight || sourWidth > destWidth)
12.  
    {
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    if ((sourWidth * destHeight) > (sourHeight * destWidth))
14.  
    {
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    width = destWidth;
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    height = (destWidth * sourHeight) / sourWidth;
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    }
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    else
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    {
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    height = destHeight;
21.  
    width = (sourWidth * destHeight) / sourHeight;
22.  
    }
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    }
24.  
    else
25.  
    {
26.  
    width = sourWidth;
27.  
    height = sourHeight;
28.  
    }
29.  
    Bitmap destBitmap = new Bitmap(destWidth, destHeight);
30.  
    Graphics g = Graphics.FromImage(destBitmap);
31.  
    g.Clear(Color.Transparent);
32.  
    //设置画布的描绘质量
33.  
    g.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality;
34.  
    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
35.  
    g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
36.  
    g.DrawImage(sourImage, new Rectangle((destWidth - width) / 2, (destHeight - height) / 2, width, height), 0, 0, sourImage.Width, sourImage.Height, GraphicsUnit.Pixel);
37.  
    g.Dispose();
38.  
    //设置压缩质量
39.  
    System.Drawing.Imaging.EncoderParameters encoderParams = new System.Drawing.Imaging.EncoderParameters();
40.  
    long[] quality = new long[1];
41.  
    quality[0] = 100;
42.  
    System.Drawing.Imaging.EncoderParameter encoderParam = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, quality);
43.  
    encoderParams.Param[0] = encoderParam;
44.  
    sourImage.Dispose();
45.  
    return destBitmap;
46.  
    }
47.  
    catch
48.  
    {
49.  
    return bitmap;
50.  
    }
51.  
    }

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