C# 图片等比例不丢真缩放

//使用方法调用GenerateHighThumbnail()方法即可
//参数oldImagePath表示要被缩放的图片路径
//参数newImagePath表示缩放后保存的图片路径
//参数width和height分别是缩放范围宽和高
public static void GenerateHighThumbnail(string oldImagePath, string newImagePath, int width, int height)
{
System.Drawing.Image oldImage = System.Drawing.Image.FromFile(oldImagePath);
int newWidth = AdjustSize(width, height, oldImage.Width, oldImage.Height).Width;
int newHeight =AdjustSize(width, height, oldImage.Width, oldImage.Height).Height;
//。。。。。。。。。。。
System.Drawing.Image thumbnailImage = oldImage.GetThumbnailImage(newWidth, newHeight,new System.Drawing.Image.GetThumbnailImageAbort(ThumbnailCallback), IntPtr.Zero);
System.Drawing.Bitmap bm = new System.Drawing.Bitmap(thumbnailImage);
//处理JPG质量的函数
System.Drawing.Imaging.ImageCodecInfo ici = GetEncoderInfo("image/jpeg");
if (ici != null)
{
System.Drawing.Imaging.EncoderParameters ep = new System.Drawing.Imaging.EncoderParameters(1);
ep.Param[0] = new System.Drawing.Imaging.EncoderParameter(System.Drawing.Imaging.Encoder.Quality, (long)100);
bm.Save(newImagePath, ici, ep);
//释放所有资源，不释放，可能会出错误。
ep.Dispose();
ep = null;
}
ici = null;
bm.Dispose();
bm = null;
thumbnailImage.Dispose();
thumbnailImage = null;
oldImage.Dispose();
oldImage = null;
}

private static bool ThumbnailCallback()
{
return false;
}

private static ImageCodecInfo GetEncoderInfo(String mimeType)
{
int j;
ImageCodecInfo[] encoders;
encoders = ImageCodecInfo.GetImageEncoders();
for (j = 0; j < encoders.Length; ++j)
{
if (encoders[j].MimeType == mimeType)
return encoders[j];
}
return null;
}

public struct PicSize
{
public int Width;
public int Height;
}

public static PicSize AdjustSize(int spcWidth, int spcHeight, int orgWidth, int orgHeight)
{
PicSize size = new PicSize();
// 原始宽高在指定宽高范围内，不作任何处理
if (orgWidth <= spcWidth && orgHeight <= spcHeight)
{
size.Width = orgWidth;
size.Height = orgHeight;
}
else
{
// 取得比例系数
float w = orgWidth / (float)spcWidth;
float h = orgHeight / (float)spcHeight;
// 宽度比大于高度比
if (w > h)
{
size.Width = spcWidth;
size.Height = (int)(w >= 1 ? Math.Round(orgHeight / w) : Math.Round(orgHeight * w));
}
// 宽度比小于高度比
else if (w < h)
{
size.Height = spcHeight;
size.Width = (int)(h >= 1 ? Math.Round(orgWidth / h) : Math.Round(orgWidth * h));
}
// 宽度比等于高度比
else
{
size.Width = spcWidth;
size.Height = spcHeight;
}
}
return size;
}