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【CSharp】缩略图生成算法

作者:Dezai.CN / 发布于2013/7/30/ 880


	代码

	Code highlighting produced by Actipro CodeHighlighter (freeware)http://www.CodeHighlighter.com/-->/// <summary>
	/// Creates a thumbnail from an existing image. Sets the biggest dimension of the
	/// thumbnail to either desiredWidth or Height and scales the other dimension down
	/// to preserve the aspect ratio
	/// </summary>
	/// <param name="imageStream">stream to create thumbnail for</param>
	/// <param name="desiredWidth">maximum desired width of thumbnail</param>
	/// <param name="desiredHeight">maximum desired height of thumbnail</param>
	/// <returns>Bitmap thumbnail</returns>
	public Bitmap CreateThumbnail(Bitmap originalBmp, int desiredWidth, int desiredHeight)
	{
	 // If the image is smaller than a thumbnail just return it
	 if (originalBmp.Width <= desiredWidth && originalBmp.Height <= desiredHeight)
	 {
	 return originalBmp;
	 }

	 int newWidth, newHeight;

	 // scale down the smaller dimension
	 if (desiredWidth * originalBmp.Height < desiredHeight * originalBmp.Width)
	 {
	 newWidth = desiredWidth;
	 newHeight = (int)Math.Round((decimal)originalBmp.Height * desiredWidth / originalBmp.Width);
	 }
	 else
	 {
	 newHeight = desiredHeight;
	 newWidth = (int)Math.Round((decimal)originalBmp.Width * desiredHeight / originalBmp.Height);
	 }

	 // This code creates cleaner (though bigger) thumbnails and properly
	 // and handles GIF files better by generating a white background for
	 // transparent images (as opposed to black)
	 // This is preferred to calling Bitmap.GetThumbnailImage()
	 Bitmap bmpOut = new Bitmap(newWidth, newHeight);
	
	 using (Graphics graphics = Graphics.FromImage(bmpOut))
	 {
	 graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
	 graphics.FillRectangle(Brushes.White, 0, 0, newWidth, newHeight);
	 graphics.DrawImage(originalBmp, 0, 0, newWidth, newHeight);
	 }

	 return bmpOut;
	}

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