用ASP.NET在网页上显示缩略图

public class getthumbnail
    inherits system.web.ui.page

#region " web 窗体设计器生成的代码 "

    '该调用是 web 窗体设计器所必需的。
    <system.diagnostics.debuggerstepthrough()> private sub initializecomponent()

    end sub

    '注意: 以下占位符声明是 web 窗体设计器所必需的。
    '不要删除或移动它。
    private designerplaceholderdeclaration as system.object

    private sub page_init(byval sender as system.object, byval e as system.eventargs) handles mybase.init
        'codegen: 此方法调用是 web 窗体设计器所必需的
        '不要使用代码编辑器修改它。
        initializecomponent()
    end sub

#end region

    private sub page_load(byval sender as system.object, byval e as system.eventargs) handles mybase.load
        '在此处放置初始化页的用户代码
        '获取几个参数，用以生成缩略图片
        '设置一个默认参数生成bitmap
        response.clear()
        try
            dim originalfilename as string = server.mappath(request("fn"))
            dim thumbnailwidth as integer = request("tw")
            dim thumbnailheight as integer = request("th")

            dim img as system.drawing.image = system.drawing.image.fromfile(originalfilename)
            dim thisformat as system.drawing.imaging.imageformat = img.rawformat
            dim newsize as system.drawing.size = me.getnewsize(thumbnailwidth, thumbnailheight, img.width, img.height)
            dim outbmp as new system.drawing.bitmap(thumbnailwidth, thumbnailheight)
            dim g as system.drawing.graphics = system.drawing.graphics.fromimage(outbmp)

            '设置画布的描绘质量
            g.compositingquality = drawing2d.compositingquality.highquality
            g.smoothingmode = drawing2d.smoothingmode.highquality
            g.interpolationmode = drawing2d.interpolationmode.highqualitybicubic
            g.clear(system.drawing.color.fromargb(255, 249, 255, 240))
            g.drawimage(img, new rectangle((thumbnailwidth - newsize.width) / 2, (thumbnailheight - newsize.height) / 2, newsize.width, newsize.height), 0, 0, img.width, img.height, graphicsunit.pixel)
            g.dispose()

            if thisformat.equals(system.drawing.imaging.imageformat.gif) then
                response.contenttype = "image/gif"
            else
                response.contenttype = "image/jpeg"
            end if

            '设置压缩质量
            dim encoderparams as new system.drawing.imaging.encoderparameters
            dim quality(0) as long
            quality(0) = 100
            dim encoderparam as new system.drawing.imaging.encoderparameter(system.drawing.imaging.encoder.quality, quality)
            encoderparams.param(0) = encoderparam

            '获得包含有关内置图像编码解码器的信息的imagecodecinfo 对象。
            dim arrayici() as system.drawing.imaging.imagecodecinfo = system.drawing.imaging.imagecodecinfo.getimageencoders()
            dim jpegici as system.drawing.imaging.imagecodecinfo = nothing
            for fwd as integer = 0 to arrayici.length - 1
                if arrayici(fwd).formatdescription.equals("jpeg") then
                    jpegici = arrayici(fwd)
                    exit for
                end if
            next

            if not jpegici is nothing then
                outbmp.save(response.outputstream, jpegici, encoderparams)
            else
                outbmp.save(response.outputstream, thisformat)
            end if
        catch ex as exception

        end try
    end sub

    function getnewsize(byval maxwidth as integer, byval maxheight as integer, byval width as integer, byval height as integer) as system.drawing.size
        dim w as double = 0.0
        dim h as double = 0.0
        dim sw as double = convert.todouble(width)
        dim sh as double = convert.todouble(height)
        dim mw as double = convert.todouble(maxwidth)
        dim mh as double = convert.todouble(maxheight)

        if sw < mw and sh < mh then
            w = sw
            h = sh
        elseif (sw / sh) > (mw / mh) then
            w = maxwidth
            h = (w * sh) / sw
        else
            h = maxheight
            w = (h * sw) / sh
        end if
        return new system.drawing.size(convert.toint32(w), convert.toint32(h))
    end function
end class