.net等比缩放生成缩略图的方法
生成缩略图是一个十分常用功能，找到了一个方法，重写部分代码，实用又好用，.net又一个生成缩略图的方法，不变形
///<summary>
///为图片生成缩略图
///</summary>
///<paramname="phyPath">原图片的路径</param>
///<paramname="width">缩略图宽</param>
///<paramname="height">缩略图高</param>
///<returns></returns>
publicSystem.Drawing.ImageGetHvtThumbnail(System.Drawing.Imageimage,intwidth,intheight)
{
Bitmapm_hovertreeBmp=newBitmap(width,height);
//从Bitmap创建一个System.Drawing.Graphics
Graphicsm_HvtGr=Graphics.FromImage(m_hovertreeBmp);
//设置
m_HvtGr.SmoothingMode=System.Drawing.Drawing2D.SmoothingMode.HighQuality;
//下面这个也设成高质量
m_HvtGr.CompositingQuality=System.Drawing.Drawing2D.CompositingQuality.HighQuality;
//下面这个设成High
m_HvtGr.InterpolationMode=System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
//把原始图像绘制成上面所设置宽高的缩小图
RectanglerectDestination=newRectangle(0,0,width,height);
intm_width,m_height;
if(image.Width*height>image.Height*width)
{
m_height=image.Height;
m_width=(image.Height*width)/height;
}
else
{
m_width=image.Width;
m_height=(image.Width*height)/width;
}
m_HvtGr.DrawImage(image,rectDestination,0,0,m_width,m_height,GraphicsUnit.Pixel);
returnm_hovertreeBmp;
}
C#缩略图生成类，采用高质量插值法实现缩略图生成，高质量,低速度呈现平滑程度，可以保持缩略图纵横比，在获取缩略图的时候一开始就根据百分比获取图片的尺寸、根据设定的大小返回图片的大小，并高质量保存缩略图图片，为原图片设置EncoderParameters对象。
以下为类文件，建议保存文件名为：ImageHelper.cs
usingSystem;
usingSystem.Collections.Generic;
usingSystem.Drawing;
usingSystem.Drawing.Imaging;
namespaceHtmlSnap
{
publicstaticclassImageHelper
{
///获取缩略图
publicstaticImageGetThumbnailImage(Imageimage,intwidth,intheight)
{
if(image==null||width<1||height<1)
returnnull;
//新建一个bmp图片
Imagebitmap=newSystem.Drawing.Bitmap(width,height);
//新建一个画板
using(Graphicsg=System.Drawing.Graphics.FromImage(bitmap))
{
//设置高质量插值法
g.InterpolationMode=System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;
//设置高质量,低速度呈现平滑程度
g.SmoothingMode=System.Drawing.Drawing2D.SmoothingMode.HighQuality;
//高质量、低速度复合
g.CompositingQuality=System.Drawing.Drawing2D.CompositingQuality.HighQuality;
//清空画布并以透明背景色填充
g.Clear(Color.Transparent);
//在指定位置并且按指定大小绘制原图片的指定部分
g.DrawImage(image,newRectangle(0,0,width,height),
newRectangle(0,0,image.Width,image.Height),
GraphicsUnit.Pixel);
returnbitmap;
}
}
///<summary>
///生成缩略图，并保持纵横比
///</summary>
///<returns>生成缩略图后对象</returns>
publicstaticImageGetThumbnailImageKeepRatio(Imageimage,intwidth,intheight)
{
SizeimageSize=GetImageSize(image,width,height);
returnGetThumbnailImage(image,imageSize.Width,imageSize.Height);
}
///<summary>
///根据百分比获取图片的尺寸
///</summary>
publicstaticSizeGetImageSize(Imagepicture,intpercent)
{
if(picture==null||percent<1)
returnSize.Empty;
intwidth=picture.Width*percent/100;
intheight=picture.Height*percent/100;
returnGetImageSize(picture,width,height);
}
///<summary>
///根据设定的大小返回图片的大小，考虑图片长宽的比例问题
///</summary>
publicstaticSizeGetImageSize(Imagepicture,intwidth,intheight)
{
if(picture==null||width<1||height<1)
returnSize.Empty;
SizeimageSize;
imageSize=newSize(width,height);
doubleheightRatio=(double)picture.Height/picture.Width;
doublewidthRatio=(double)picture.Width/picture.Height;
intdesiredHeight=imageSize.Height;
intdesiredWidth=imageSize.Width;
imageSize.Height=desiredHeight;
if(widthRatio>0)
imageSize.Width=Convert.ToInt32(imageSize.Height*widthRatio);
if(imageSize.Width>desiredWidth)
{
imageSize.Width=desiredWidth;
imageSize.Height=Convert.ToInt32(imageSize.Width*heightRatio);
}
returnimageSize;
}
///<summary>
///获取图像编码解码器的所有相关信息
///</summary>
///<paramname="mimeType">包含编码解码器的多用途网际邮件扩充协议(MIME)类型的字符串</param>
///<returns>返回图像编码解码器的所有相关信息</returns>
publicstaticImageCodecInfoGetCodecInfo(stringmimeType)
{
ImageCodecInfo[]CodecInfo=ImageCodecInfo.GetImageEncoders();
foreach(ImageCodecInfoiciinCodecInfo)
{
if(ici.MimeType==mimeType)returnici;
}
returnnull;
}
publicstaticImageCodecInfoGetImageCodecInfo(ImageFormatformat)
{
ImageCodecInfo[]encoders=ImageCodecInfo.GetImageEncoders();
foreach(ImageCodecInfoicfinencoders)
{
if(icf.FormatID==format.Guid)
{
returnicf;
}
}
returnnull;
}
publicstaticvoidSaveImage(Imageimage,stringsavePath,ImageFormatformat)
{
SaveImage(image,savePath,GetImageCodecInfo(format));
}
///<summary>
///高质量保存图片
///</summary>
privatestaticvoidSaveImage(Imageimage,stringsavePath,ImageCodecInfoici)
{
//设置原图片对象的EncoderParameters对象
EncoderParametersparms=newEncoderParameters(1);
EncoderParameterparm=newEncoderParameter(Encoder.Quality,((long)95));
parms.Param[0]=parm;
image.Save(savePath,ici,parms);
parms.Dispose();
}
}
}