等比例缩放图片（C#）

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;
}
}

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