c#生成缩略图的实现方法

 private void savethumbnail(bitmap originbitmap, int width, int height, string directory, string filename, string extension)
{
    var physicalpath = directory + filename + extension;

    using (var newimage = new bitmap(width, height))
    {
        using (var graphic = getgraphic(originbitmap, newimage))
        {
            graphic.drawimage(originbitmap, 0, 0, width, height);
            using (var encoderparameters = new encoderparameters(1))
            {
                encoderparameters.param[0] = new encoderparameter(encoder.quality, 100l);
                newimage.save(physicalpath,
                            imagecodecinfo.getimageencoders()
                                .where(x => x.filenameextension.contains(extension.toupperinvariant()))
                                .firstordefault(),
                            encoderparameters);
            }
        }
    }           
}

private graphics getgraphic(image originimage, bitmap newimage)
{
    newimage.setresolution(originimage.horizontalresolution, originimage.verticalresolution);
    var graphic = graphics.fromimage(newimage);
    graphic.interpolationmode = system.drawing.drawing2d.interpolationmode.highqualitybicubic;
    graphic.smoothingmode = system.drawing.drawing2d.smoothingmode.highquality;
    graphic.pixeloffsetmode = system.drawing.drawing2d.pixeloffsetmode.highquality;
    graphic.compositingquality = system.drawing.drawing2d.compositingquality.highquality;
    return graphic;
}