用VB.net调整图像大小、压缩和平滑

我花了相当长的时间在谷歌上搜索这篇文章，读了很多文章，但我似乎一直在兜圈子，现在非常困惑，似乎什么地方都没找到

我试图得到一个图像的4个不同大小的版本，为了实现这一点，我有一个大小的数组，并循环下面的函数

这是可行的，并且达到了预期的效果，除了较小的图像非常块状，我无法获得平滑效果以达到我预期的效果

对于老式的ASP Classic，我使用了Persits ASPUpload/jpeg插件，它做了很好的平滑调整。有了.NET，我很挣扎

Public Shared Sub ResizeImages(FileName, NewFileName, maxWidth, maxHeight, uploadDir, qualityPercent)

    Dim originalImg As System.Drawing.Image = System.Drawing.Image.FromFile(uploadDir & FileName)

    Dim aspectRatio As Double
    Dim newHeight As Integer
    Dim newWidth As Integer

    '*** Calculate Size ***'
    If originalImg.Width > maxWidth Or originalImg.Height > maxHeight Then
        If originalImg.Width >= originalImg.Height Then ' image is wider than tall
            newWidth = maxWidth
            aspectRatio = originalImg.Width / maxWidth
            newHeight = originalImg.Height / aspectRatio
        Else ' image is taller than wide
            newHeight = maxHeight
            aspectRatio = originalImg.Height / maxHeight
            newWidth = originalImg.Width / aspectRatio
        End If
    Else ' if image is not larger than max then keep original size
        newWidth = originalImg.Width
        newHeight = originalImg.Height
    End If

    Dim newImg As New Bitmap(originalImg, CInt(newWidth), CInt(newHeight)) '' blank canvas
    Dim canvas As Graphics = Graphics.FromImage(newImg) 'graphics element

    '*** compress ***'
    Dim myEncoderParameters As EncoderParameters
    myEncoderParameters = New EncoderParameters(1)
    ' set quality level based on "resolution" variable
    Dim myEncoderParameter = New EncoderParameter(System.Drawing.Imaging.Encoder.Quality, CType(qualityPercent, Int32))
    myEncoderParameters.Param(0) = myEncoderParameter

    '*** Save As  ***'
    canvas.SmoothingMode = Drawing.Drawing2D.SmoothingMode.AntiAlias
    canvas.DrawImage(newImg, New Point(0, 0))
    newImg.Save(uploadDir & NewFileName, getCodec("image/jpeg"), myEncoderParameters)

    '*** Close ***'
    originalImg.Dispose()
    newImg.Dispose()
    '*** Nothing ***'
    newImg = Nothing
    originalImg = Nothing

End Sub

Public Shared Function getCodec(getThis) As Drawing.Imaging.ImageCodecInfo
    Dim output As Drawing.Imaging.ImageCodecInfo
    Dim codecs As Imaging.ImageCodecInfo() = Imaging.ImageCodecInfo.GetImageEncoders
    For Each codec As Imaging.ImageCodecInfo In codecs
        If codec.MimeType = getThis Then
            output = codec
        End If
    Next codec
    Return output
End Function

我觉得我可能在这里把类型弄混了

在执行上述功能的过程中，我有一个

系统.Drawing.Image

、一个

位图

和一个

图形

对象，我觉得我可能试图将平滑应用到错误的元素，或者在错误的编码阶段

System.Drawing.Image

对象加载保存在服务器上的文件，然后我计算纵横比和所需的新大小，创建此大小的新

位图

，并将其保存到

图形

对象

这是正确的吗

我需要修改什么才能实现更平滑的调整

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如往常一样，任何帮助都将不胜感激。

尝试使用插值模式

Private imgSource As System.Drawing.Image
Private imgOutput As System.Drawing.Image
Public Function Resize(ByVal intPercent As Integer, ByVal intType As Integer)
    'resize the image by percent
    Dim intX, intY As Integer
    intX = Int(imgSource.Width / 100 * intPercent)
    intY = Int(imgSource.Height / 100 * intPercent)
    Dim bm As Drawing.Bitmap = New System.Drawing.Bitmap(intX, intY)
    Dim g As System.Drawing.Graphics = Drawing.Graphics.FromImage(bm)

    Select Case intType
        Case 0
            g.InterpolationMode = Drawing.Drawing2D.InterpolationMode.Default
        Case 1
            g.InterpolationMode = Drawing.Drawing2D.InterpolationMode.High
        Case 2
            g.InterpolationMode = Drawing.Drawing2D.InterpolationMode.HighQualityBilinear
        Case 3
            g.InterpolationMode = Drawing.Drawing2D.InterpolationMode.HighQualityBicubic
    End Select

    g.DrawImage(imgSource, 0, 0, intX, intY)
    imgOutput = bm

End Function

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嗨，谢谢你的回复。我试过你的建议，但我看不出任何插值情况下的输出图像有什么不同，也尝试过将SmoothingMode更改为High Quality，这也没有明显的区别。你的代码对我来说非常好，vs2010和.net4。源图像5616 x 3744 996.77 KB JPG，输出图像300 x 200 8.79 KB JPG。qualityPercent是80。哦，也许我只是想把东西做得太小，我想把显示图像做成180x250左右的样子，它们会变得块状。1800 x 1800的放大图像与您的修改很好。如果您将图像转换为非常小的图像，请不要使用AntiAlias。你需要锐化效果。