调整大小后白色图像获得灰色边框

Question

我正在搜索谷歌的某种解决方案，我发现了一个，我试图在我的代码中实现它，但它不起作用。问题是，在调整白色图像大小后，它们会变成灰色边框。

以下是我找到的解决方案的链接：

它说： 出现此问题的原因是您正在将图像数据插值为 新的大小，但沿着边缘没有像素插值和.NET 默认情况下，这些边使用黑色像素。要解决此问题，您需要使用 DrawImage调用中的ImageAttributes类......

https://groups.google.com/group/microsoft.public.dotnet.framework.drawing/browse_thread/thread/d834851b49274fd9/81a4fd43694457ac?hl=en&lnk=st&q=DrawImage+resized+border#81a4fd43694457ac

代码1：这是我执行ImageAttributes的代码：

Private Shared Function ResizeImageFile(ByVal imageFile As Byte(), ByVal targetSize As Integer) As Byte()

    Using oldImage As System.Drawing.Image = System.Drawing.Image.FromStream(New MemoryStream(imageFile))

        Dim newSize As Size = CalculateDimensions(oldImage.Size, targetSize)

        Using newImage As New Bitmap(newSize.Width, newSize.Height, PixelFormat.Format32bppRgb)

            Using canvas As Graphics = Graphics.FromImage(newImage)

                Using ia As New ImageAttributes

                    ia.SetWrapMode(Drawing2D.WrapMode.TileFlipXY)
                    canvas.SmoothingMode = SmoothingMode.AntiAlias
                    canvas.InterpolationMode = InterpolationMode.HighQualityBicubic
                    canvas.PixelOffsetMode = PixelOffsetMode.HighQuality
                    canvas.DrawImage(oldImage, New Rectangle(New Point(0, 0), newSize), 0, 0, newImage.Width, newImage.Height, GraphicsUnit.Pixel, ia)

                    Dim m As New MemoryStream()

                    newImage.Save(m, ImageFormat.Png)
                    Return m.GetBuffer()

                End Using

            End Using

        End Using

    End Using

End Function

Private Shared Function CalculateDimensions(ByVal oldSize As Size, ByVal targetSize As Integer) As Size

    Dim newSize As New Size()

    If oldSize.Height > oldSize.Width Then

        newSize.Width = CInt((oldSize.Width * (CSng(targetSize) / CSng(oldSize.Height))))
        newSize.Height = targetSize

    Else

        newSize.Width = targetSize
        newSize.Height = CInt((oldSize.Height * (CSng(targetSize) / CSng(oldSize.Width))))

    End If

    Return newSize

End Function

代码2：白色图像上的灰色边缘代码

以下是调整大小后的图片：

新图片尺寸宽度= 400px

Private Shared Function ResizeImageFile(ByVal imageFile As Byte(), ByVal targetSize As Integer) As Byte()

    Using oldImage As System.Drawing.Image = System.Drawing.Image.FromStream(New MemoryStream(imageFile))

        Dim newSize As Size = CalculateDimensions(oldImage.Size, targetSize)

        Using newImage As New Bitmap(newSize.Width, newSize.Height, PixelFormat.Format32bppRgb)

            Using canvas As Graphics = Graphics.FromImage(newImage)

                    canvas.SmoothingMode = SmoothingMode.AntiAlias
                    canvas.InterpolationMode = InterpolationMode.HighQualityBicubic
                    canvas.PixelOffsetMode = PixelOffsetMode.HighQuality
                    canvas.DrawImage(oldImage, New Rectangle(New Point(0, 0), newSize))

                    Dim m As New MemoryStream()

                    newImage.Save(m, ImageFormat.Png)
                    Return m.GetBuffer()

            End Using

        End Using

    End Using

End Function

Private Shared Function CalculateDimensions(ByVal oldSize As Size, ByVal targetSize As Integer) As Size

    Dim newSize As New Size()

    If oldSize.Height > oldSize.Width Then

        newSize.Width = CInt((oldSize.Width * (CSng(targetSize) / CSng(oldSize.Height))))
        newSize.Height = targetSize

    Else

        newSize.Width = targetSize
        newSize.Height = CInt((oldSize.Height * (CSng(targetSize) / CSng(oldSize.Width))))

    End If

    Return newSize

End Function

更新30.07.2011。：

CODE 1解决了白色图像上灰色边框的问题，但有新问题。问题出在这行代码中：

canvas.DrawImage（oldImage，New Rectangle（New Point（0,0），newSize），0,0，newImage.Width，newImage.Height，GraphicsUnit.Pixel，ia）

使用此代码，我可以获得具有所需宽度和高度的输出图像，并且没有灰色边框，但不会缩放oldImage。

例如：

如果我想上传，调整大小并保存有形的图像，例如640x480px，而targetSize是400px。作为输出，我得到一个宽度为400px，高度：300px的图像，没有灰色边框，但oldImage没有调整大小/缩放到400px。在这种情况下，oldImage以原始分辨率绘制。 如何缩放oldImage以正确绘制？有人能指出我正确的解决方案或修改代码吗？

感谢所有人，但我找到了解决所有问题的方法。

由于以下代码行，CODE 1 无法正常运行：

canvas.DrawImage（oldImage，New Rectangle（New Point（0,0），newSize），0,0，newImage.Width，newImage.Height，GraphicsUnit.Pixel，ia）

SOLUTION：

canvas.DrawImage（oldImage，New Rectangle（New Point（0,0），newSize），0,0， oldImage.Width ， oldImage.Height ，GraphicsUnit .Pixel，ia）

这是完整的工作代码（没有灰色/黑色边框的已调整大小的图片）：

Private Shared Function ResizeImageFile(ByVal imageFile As Byte(), ByVal targetSize As Integer) As Byte()

    Using oldImage As System.Drawing.Image = System.Drawing.Image.FromStream(New MemoryStream(imageFile))

        Dim newSize As Size = CalculateDimensions(oldImage.Size, targetSize)

        Using newImage As New Bitmap(newSize.Width, newSize.Height, PixelFormat.Format32bppRgb)

            Using canvas As Graphics = Graphics.FromImage(newImage)

                Using ia As New ImageAttributes

                    ia.SetWrapMode(Drawing2D.WrapMode.TileFlipXY)
                    canvas.SmoothingMode = SmoothingMode.AntiAlias
                    canvas.InterpolationMode = InterpolationMode.HighQualityBicubic
                    canvas.PixelOffsetMode = PixelOffsetMode.HighQuality
                    canvas.DrawImage(oldImage, New Rectangle(New Point(0, 0), newSize), 0, 0, oldImage.Width, oldImage.Height, GraphicsUnit.Pixel, ia)

                    Dim m As New MemoryStream()

                    newImage.Save(m, ImageFormat.Png)
                    Return m.GetBuffer()

                End Using

            End Using

        End Using

    End Using

End Function

Private Shared Function CalculateDimensions(ByVal oldSize As Size, ByVal targetSize As Integer) As Size

    Dim newSize As New Size()

    If oldSize.Height > oldSize.Width Then

        newSize.Width = CInt((oldSize.Width * (CSng(targetSize) / CSng(oldSize.Height))))
        newSize.Height = targetSize

    Else

        newSize.Width = targetSize
        newSize.Height = CInt((oldSize.Height * (CSng(targetSize) / CSng(oldSize.Width))))

    End If

    Return newSize

End Function

Answer 1

这是我所拥有的类中的一个函数，你将不得不替换一些类属性（ThumbNailSize.Width，ThumbNailSize.Height）：

public void ResizeImage(HttpPostedFile fil, string sPhysicalPath, 
                              string sOrgFileName,string sThumbNailFileName,
                              ImageFormat oFormat, int rez)
{

    try
    {

        System.Drawing.Image oImg = System.Drawing.Image.FromStream(fil.InputStream);

        decimal pixtosubstract = 0;
        decimal percentage;

        //default
        Size ThumbNailSizeToUse = new Size();
        if (ThumbNailSize.Width < oImg.Size.Width || ThumbNailSize.Height < oImg.Size.Height)
        {
            if (oImg.Size.Width > oImg.Size.Height)
            {
                percentage = (((decimal)oImg.Size.Width - (decimal)ThumbNailSize.Width) / (decimal)oImg.Size.Width);
                pixtosubstract = percentage * oImg.Size.Height;
                ThumbNailSizeToUse.Width = ThumbNailSize.Width;
                ThumbNailSizeToUse.Height = oImg.Size.Height - (int)pixtosubstract;
            }
            else
            {
                percentage = (((decimal)oImg.Size.Height - (decimal)ThumbNailSize.Height) / (decimal)oImg.Size.Height);
                pixtosubstract = percentage * (decimal)oImg.Size.Width;
                ThumbNailSizeToUse.Height = ThumbNailSize.Height;
                ThumbNailSizeToUse.Width = oImg.Size.Width - (int)pixtosubstract;
            }

        }
        else
        {
            ThumbNailSizeToUse.Width = oImg.Size.Width;
            ThumbNailSizeToUse.Height = oImg.Size.Height;
        }

        Bitmap bmp = new Bitmap(ThumbNailSizeToUse.Width, ThumbNailSizeToUse.Height);
        bmp.SetResolution(rez, rez);
        System.Drawing.Image oThumbNail = bmp;

        bmp = null;

        Graphics oGraphic = Graphics.FromImage(oThumbNail);

        oGraphic.CompositingQuality = CompositingQuality.HighQuality;

        oGraphic.SmoothingMode = SmoothingMode.HighQuality;

        oGraphic.InterpolationMode = InterpolationMode.HighQualityBicubic;

        Rectangle oRectangle = new Rectangle(0, 0, ThumbNailSizeToUse.Width, ThumbNailSizeToUse.Height);

        oGraphic.DrawImage(oImg, oRectangle);

        oThumbNail.Save(sPhysicalPath  + sThumbNailFileName, oFormat);

        oImg.Dispose();

    }
    catch (Exception ex)
    {
        Response.Write(ex.Message);
    }

}