c# - FreeImage 的透明度变得疯狂

Question

在我的程序中，我想加载一个 PNG 或 ICO 文件（具有透明度），然后将其保存为具有透明度的 ICO 文件。

这是用于测试的随机 png 图像：

...如您所见，它具有透明度。

但是当我尝试将其转换为 ICO 时，结果如下：

（图片取自 Windows 资源管理器）

所有的黑色都消失了。

我尝试使用专业软件如 photoshop 或 ToyCon 进行相同的转换，结果 ICO 文件没有这个问题。

这是我的代码，是我第一次使用 FreeImage，我对图像和 alpha 通道或透明度不太了解：

Imports FreeImageAPI

'Dim img As FreeImageAPI.FIBITMAP = FreeImage.Load(format, file, FREE_IMAGE_LOAD_FLAGS.ICO_MAKEALPHA)

Public Class Form1

Dim file As String = "C:\Users\Administrador.ELEKTRO-PC\Desktop\auricular 5.png"

Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Shown

    Dim format As FreeImageAPI.FREE_IMAGE_FORMAT = FreeImage.GetFileType(file, 32)

    Dim img As FreeImageAPI.FIBITMAP = FreeImage.LoadEx(file)

    Dim Transparency As Byte() = New Byte(0) {}

    FreeImage.SetTransparencyTable(img, Transparency)

    FreeImage.Save(FREE_IMAGE_FORMAT.FIF_ICO, img, "c:\test.ico", FREE_IMAGE_SAVE_FLAGS.DEFAULT)

End Sub

End Class

Answer 1

完毕。

我已经删除了透明度表，看起来一切正常，最后不需要设置透明度，我还做了一个新手帮助类来管理库的一些基本功能（转换图像，旋转，灰度，调整大小...... ) 以一种简单的方式：

#Region " FreeImage Helper "

' [ FreeImage Helper ]
'
' // By Elektro H@cker
'
'
' INSTRUCTIONS:
' 1. ADD A REFERENCE FOR "FreeImageNET.dll" IN THE PROJECT.
' 2. ADD THE "FREEIMAGE.DLL" IN THE PROJECT.
'
'
' Examples :
'
' MsgBox(FreeImageHelper.Is_Avaliable() ' Result: True
' MsgBox(FreeImageHelper.Get_Version()  ' Result: 3.15.1
' MsgBox(FreeImageHelper.Get_ImageFormat("C:\Test.png")) ' Result: PNG
'
' FreeImageHelper.Convert("C:\Test.png", "C:\Test.ico", FreeImageAPI.FREE_IMAGE_FORMAT.FIF_ICO)
' FreeImageHelper.Convert(New Bitmap("C:\Test.png"), "C:\Test.jpg", FreeImageAPI.FREE_IMAGE_FORMAT.FIF_JPEG, FreeImageAPI.FREE_IMAGE_SAVE_FLAGS.JPEG_SUBSAMPLING_444 Or FreeImageAPI.FREE_IMAGE_SAVE_FLAGS.JPEG_QUALITYSUPERB)
'
' PictureBox1.BackgroundImage = FreeImageHelper.GrayScale(New Bitmap("C:\Test.bmp"))
' PictureBox1.BackgroundImage = FreeImageHelper.GrayScale("C:\Test.bmp")
'
' PictureBox1.BackgroundImage = FreeImageHelper.Resize(New Bitmap("C:\Test.bmp"), 32, 32)
' PictureBox1.BackgroundImage = FreeImageHelper.Resize("C:\Test.bmp", 64, 128)
'
' PictureBox1.BackgroundImage = FreeImageHelper.Rotate(New Bitmap("C:\Test.bmp"), 90)
' PictureBox1.BackgroundImage = FreeImageHelper.Rotate("C:\Test.bmp", -90)
'
' PictureBox1.BackgroundImage = FreeImageHelper.Thumbnail(New Bitmap("C:\Test.png"), 64, True)
' PictureBox1.BackgroundImage = FreeImageHelper.Thumbnail("C:\Test.png", 64, True)



Imports FreeImageAPI

Public Class FreeImageHelper

' <summary>
' Checks if <i>FreeImage.dll</i> is avaliable on the system.
' </summary>
Public Shared Function Is_Avaliable() As Boolean
    Return FreeImage.IsAvailable
End Function

' <summary>
' Gets the version of FreeImage.dll.
' </summary>
Shared Function Get_Version() As String
    Return FreeImage.GetVersion
End Function

' <summary>
' Gets the image format of a image file.
' </summary>
Shared Function Get_ImageFormat(ByVal File As String) As String
    Return FreeImage.GetFileType(File, 0).ToString.Substring(4)
End Function

' <summary>
' Convert a Bitmap object between image formats and save it to disk.
' </summary>
Shared Sub Convert(ByVal bmp As System.Drawing.Bitmap, _
                   ByVal Output As String, _
                   ByVal NewFormat As FREE_IMAGE_FORMAT, _
                   Optional ByVal SaveFlags As FREE_IMAGE_SAVE_FLAGS = FREE_IMAGE_SAVE_FLAGS.DEFAULT)

    Try
        FreeImage.SaveBitmap(bmp, Output, NewFormat, SaveFlags)
    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
    End Try

End Sub

' <summary>
' Convert a image file between image formats and save it to disk.
' </summary>
Shared Sub Convert(ByVal File As String, _
                   ByVal Output As String, _
                   ByVal NewFormat As FREE_IMAGE_FORMAT, _
                   Optional ByVal SaveFlags As FREE_IMAGE_SAVE_FLAGS = FREE_IMAGE_SAVE_FLAGS.DEFAULT)

    Try
        FreeImage.Save(NewFormat, FreeImage.LoadEx(File), Output, SaveFlags)
    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
    End Try

End Sub

' <summary>
' GrayScales a Bitmap object.
' </summary>
Shared Function GrayScale(ByVal bmp As System.Drawing.Bitmap) As System.Drawing.Bitmap

    Try

        Dim ImageStream As New System.IO.MemoryStream
        bmp.Save(ImageStream, bmp.RawFormat)

        Dim Image As FIBITMAP = FreeImage.LoadFromStream(ImageStream)
        ImageStream.Dispose()

        Return FreeImage.GetBitmap(FreeImage.ConvertToGreyscale(Image))

    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
        Return Nothing
    End Try

End Function

' <summary>
' GrayScales a image file.
' </summary>
Shared Function GrayScale(ByVal File As String) As System.Drawing.Bitmap

    Try
        Return FreeImage.GetBitmap(FreeImage.ConvertToGreyscale(FreeImage.LoadEx(File)))
    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
        Return Nothing
    End Try

End Function

' <summary>
' Resizes a Bitmap object.
' </summary>
Shared Function Resize(ByVal bmp As System.Drawing.Bitmap, _
                       ByVal X As Int32, _
                       ByVal Y As Int32, _
                       Optional ByVal Quality As FREE_IMAGE_FILTER = FREE_IMAGE_FILTER.FILTER_BILINEAR) As System.Drawing.Bitmap

    Try

        Dim ImageStream As New System.IO.MemoryStream
        bmp.Save(ImageStream, bmp.RawFormat)

        Dim Image As FIBITMAP = FreeImage.LoadFromStream(ImageStream)
        ImageStream.Dispose()

        Return FreeImage.GetBitmap(FreeImage.Rescale(Image, X, Y, Quality))

    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
        Return Nothing
    End Try

End Function

' <summary>
' Resizes a image file.
' </summary>
Shared Function Resize(ByVal File As String, _
                       ByVal X As Int32, _
                       ByVal Y As Int32, _
                       Optional ByVal Quality As FREE_IMAGE_FILTER = FREE_IMAGE_FILTER.FILTER_BILINEAR) As System.Drawing.Bitmap

    Try

        Return FreeImage.GetBitmap(FreeImage.Rescale(FreeImage.LoadEx(File), X, Y, Quality))

    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
        Return Nothing
    End Try

End Function

' <summary>
' Rotates a Bitmap object.
' </summary>
Shared Function Rotate(ByVal bmp As System.Drawing.Bitmap, _
                       ByVal Angle As Double) As System.Drawing.Bitmap

    Try

        Dim ImageStream As New System.IO.MemoryStream
        bmp.Save(ImageStream, bmp.RawFormat)

        Dim Image As FIBITMAP = FreeImage.LoadFromStream(ImageStream)
        ImageStream.Dispose()

        Return FreeImage.GetBitmap(FreeImage.Rotate(Image, Angle))

    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
        Return Nothing
    End Try

End Function

' <summary>
' Rotates a image file.
' </summary>
Shared Function Rotate(ByVal File As String, _
                       ByVal Angle As Double) As System.Drawing.Bitmap

    Try

        Return FreeImage.GetBitmap(FreeImage.Rotate(FreeImage.LoadEx(File), Angle))

    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
        Return Nothing
    End Try

End Function

' <summary>
' Returns a Thumbnail of a Bitmap object.
' </summary>
Shared Function Thumbnail(ByVal bmp As System.Drawing.Bitmap, _
                               ByVal size As Int32, _
                               ByVal convert As Boolean) As System.Drawing.Bitmap

    Try

        Dim ImageStream As New System.IO.MemoryStream
        bmp.Save(ImageStream, bmp.RawFormat)

        Dim Image As FIBITMAP = FreeImage.LoadFromStream(ImageStream)
        ImageStream.Dispose()

        Return FreeImage.GetBitmap(FreeImage.MakeThumbnail(Image, size, convert))

    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
        Return Nothing
    End Try

End Function

' <summary>
' Returns a Thumbnail of a image file.
' </summary>
Shared Function Thumbnail(ByVal File As String, _
                               ByVal size As Int32, _
                               ByVal convert As Boolean) As System.Drawing.Bitmap

    Try
        Return FreeImage.GetBitmap(FreeImage.MakeThumbnail(FreeImage.LoadEx(File), size, convert))
    Catch ex As Exception
        ' Throw New Exception(ex.Message)
        MsgBox(ex.Message)
        Return Nothing
    End Try

End Function

End Class

#End Region