ASP.NET 从流中保存.jpg文件的代码不会保存.gif文件

Question

我收到错误A Graphics object cannot be created from an image that has an indexed pixel format.

下面的代码在我的服务器上保存了一个图像，当

imageURL="http://www.wijny.nl/imagestore/product/375/villamariaestateprivatebinsauvignonblancmarlboroughnewzealand10126029.jpg"

代码在以下情况下不会保存任何图像

imageURL="http://www.wijny.nl/imagestore/product/377/villamariasinglevineyardcha.gif"

我看到的唯一区别是图像源的格式，.jpg文件存储正确，.gif文件存储不正确。如何确保代码保存任何类型的图像，无论是.png、.jpg还是.gif？

Dim imgRequest As WebRequest
Dim imgResponse As WebResponse
Dim imgStream As Stream
imgRequest = WebRequest.Create(imageURL)
Dim localImageFilename as String = 'test.jpg'
Try
    imgResponse = imgRequest.GetResponse()
    imgStream = imgResponse.GetResponseStream()
Catch ex As Exception
    LogError("imgRequest.GetResponse", ex.Message)
End Try
imgRemoteImage = System.Drawing.Image.FromStream(imgStream)
localImagePath = Server.MapPath(ConfigurationManager.AppSettings("photospath").ToString) + localImageFilename
ResizeAndSaveImage(1200, 1200, localImagePath, imgRemoteImage)
Private Function ResizeAndSaveImage(ByVal maxWidth As Integer, ByVal maxHeight As Integer, ByVal path As String, ByVal img As System.Drawing.Image) As Boolean
    Dim newWidth, newHeight As Integer
    Dim scaleFactor As Double
    Dim bResult As Boolean
    newWidth = img.Width
    newHeight = img.Height
    If img.Width > maxWidth Or img.Height > maxHeight Then
        If img.Width > maxWidth Then
            scaleFactor = maxWidth / img.Width
            newWidth = Math.Round(img.Width * scaleFactor, 0)
            newHeight = Math.Round(img.Height * scaleFactor, 0)
        End If
        If newHeight > maxHeight Then
            scaleFactor = maxHeight / newHeight
            newWidth = Math.Round(newWidth * scaleFactor, 0)
            newHeight = Math.Round(newHeight * scaleFactor, 0)
        End If
    End If
        Try
            Dim bMap As New Bitmap(newWidth, newHeight, img.PixelFormat)
            Dim gr As System.Drawing.Graphics = System.Drawing.Graphics.FromImage(bMap)
            gr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality
            gr.CompositingQuality = System.Drawing.Drawing2D.CompositingQuality.HighQuality
            gr.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High
            Dim rectDestination As New System.Drawing.Rectangle(0, 0, newWidth, newHeight)
            gr.DrawImage(img, rectDestination, 0, 0, img.Width, img.Height, GraphicsUnit.Pixel)
            bMap.Save(path, System.Drawing.Imaging.ImageFormat.Jpeg) 
            bMap.Dispose()
            bResult = True
        Catch ex As Exception
        End Try
    Return bResult
End Function

Answer 1

向函数添加一个参数：

Private Function ResizeAndSaveImage(ByVal maxWidth As Integer, ByVal maxHeight As Integer, ByVal path As String, ByVal img As System.Drawing.Image, byval Extension as String) As Boolean ' where extension comes from your filename...it'll either be GIF, JPG, or PNG.

然后在保存位图的位置执行以下操作：

if Extension = "JPG" then
    bMap.Save(path, System.Drawing.Imaging.ImageFormat.Jpeg) 
elseif Extension = "GIF" then
    bMap.Save(path, System.Drawing.Imaging.ImageFormat.Gif)
else
    bMap.Save(path, System.Drawing.Imaging.ImageFormat.Png) 
end if

您可能还希望包括检查以查看是否传递了有效的扩展，但这取决于您正在做什么以及您是否认为有必要。

Answer 2

原来

我不得不更改PixelFormat参数，

这适用于.gif文件：bMap = New Bitmap(newWidth, newHeight, PixelFormat.Format24bppRgb)