news:1149499618.138889.263100@y43g2000cwc.googlegroups.com...
> In a previous post I have been asking about a way to test Alpha
> Transparency.
> Bob and Michael have kindly provided some ideas.
>
> Here I would like to share the function I have prepared, for the
> purpose to improve it.
> Frankly, I am not clear about the exact meaning of some pixel format
> (max, gdi, etc.) and I hope I  have put them under the right "case". I
> have made only some superficial test and it seems to work.
> Note that the purpose is to test ALPHA transparency (not transparency
> in indexed-color image) this is useful because some programs do not
> support it (as for instance IE 6)
> I enclose all the source, included the handler for a button (button1)
> on a form.
>
> The logic I use is to make first a "preliminary quick check", based on
> the consideration that, if Alpha transparency is used, in the 95% of
> the cases it "shows up" around the picture. If the check is
> undeterminate, the user can specify to perform a full scan (this needs
> to be improved much).
>
> Please, suggest all the code improvement that are useful to improve
> this test and it's
> speed ...
>
>
> Imports System.Drawing.Imaging
>
> Public Class Form1
>    Inherits System.Windows.Forms.Form
>
> #Region " Windows Form Designer generated code "
> #End Region
>
>    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> System.EventArgs) Handles Button1.Click
>
>        'Dialog to load an image from disk
>
>        Dim FileImage As String
>
>        Dim Ofd As New OpenFileDialog
>        With Ofd
>            .Filter = "All files (*.*)|*.*" & _
>                      "|Bitmap files (*.bmp)|*.bmp" & _
>                      "|Portable Network Graphics files (*.png)|*.png"
> & _
>                      "|Jpeg files (*.jpg)|*.jpg" & _
>                      "|Tiff files (*.tif)|*.tif" & _
>                      "|GIF files (*.gif)|*.gif" & _
>                      "|Windows Meta files (*.wmf)|*.wmf" & _
>                      "|Windows Icon files (*.ico)|*.ico"
>            If Not .ShowDialog.Equals(DialogResult.OK) Then Exit Sub
>            FileImage = .FileName
>            .Dispose()
>        End With
>
>        Dim b As Bitmap
>        Dim i As Image
>
>        Try
>            i = Image.FromFile(FileImage)
>        Catch ex As Exception
>            MsgBox("Invalid picture or unsupported format")
>            Exit Sub
>        End Try
>
>        If TypeOf (i) Is Bitmap Then
>            b = DirectCast(i, Bitmap)
>            MsgBox("Uses Alpha transparency: " & _
>                   Me.ImageUsesAlphaTransparency(b, True).ToString)
>        Else
>            MsgBox("Not a bitmap")
>        End If
>
>    End Sub
>
>    Public Function ImageUsesAlphaTransparency(ByVal Bitmap As Bitmap,
> _
>                                               ByVal FullCheck As
> Boolean) As Boolean
>        With Bitmap
>
>            Select Case .PixelFormat
>                Case PixelFormat.Indexed, _
>                     PixelFormat.Format16bppGrayScale, _
>                     PixelFormat.Format16bppRgb555, _
>                     PixelFormat.Format16bppRgb565, _
>                     PixelFormat.Format1bppIndexed, _
>                     PixelFormat.Format24bppRgb, _
>                     PixelFormat.Format32bppRgb, _
>                     PixelFormat.Format48bppRgb, _
>                     PixelFormat.Format4bppIndexed, _
>                     PixelFormat.Format8bppIndexed, _
>                     PixelFormat.Max  '(what's that?)
>
>                    Return False
>
>                Case PixelFormat.Format16bppArgb1555, _
>                     PixelFormat.Format32bppArgb, _
>                     PixelFormat.Format32bppPArgb, _
>                     PixelFormat.Format64bppArgb, _
>                     PixelFormat.Format64bppPArgb, _
>                     PixelFormat.Gdi, _
>                     PixelFormat.Alpha, _
>                     PixelFormat.PAlpha, _
>                     PixelFormat.DontCare, _
>                     PixelFormat.Canonical, _
>                     PixelFormat.Undefined, _
>                     PixelFormat.Extended
>
>                    'Quick check of the 4 corners and center
>                    '(as, usually, transparency is used around a
> picture)
>
>                    If .GetPixel(0, 0).A < 255 Then Return True
>                    If .GetPixel(Bitmap.Width - 1, Bitmap.Height - 1).A
> < 255 Then Return True
>                    If .GetPixel(0, Bitmap.Height - 1).A < 255 Then
> Return True
>                    If .GetPixel(Bitmap.Width - 1, 0).A < 255 Then
> Return True
>                    If .GetPixel(Bitmap.Width \ 2, Bitmap.Height \ 2).A
> < 255 Then Return True
>
>                    'further checking needed (suggest code improvement)
>
>                    If FullCheck Then
>                        For x As Integer = 0 To .Width - 1
>                            For y As Integer = 0 To .Height - 1
>                                If .GetPixel(x, y).A < 255 Then Return
> True
>                            Next y
>                        Next x
>                        Return False
>                    Else
>                        Return True 'conservative choice
>                    End If
>
>                Case Else
>                    MsgBox("Unexpected event")
>                    Return True
>
>            End Select
>
>        End With
>
>    End Function
>
> End Class
>
>
>
>
> -tommaso
>

> Instead of the GetPixel method use LockBits.
>
> You can see how I test for Alpha bits in the "Get Alpha Bitmap from 32 bit
> Icon." example on my site:
> http://www.dotnetrix.co.uk/misc.html
>
> I like the quick test in your example and may incorporate that in mine.
>
> --
> Mick Doherty
> http://dotnetrix.co.uk/nothing.html
>
>
> <tommaso.gasta***@uniroma1.it> wrote in message
> news:1149499618.138889.263100@y43g2000cwc.googlegroups.com...
> > In a previous post I have been asking about a way to test Alpha
> > Transparency.
> > Bob and Michael have kindly provided some ideas.
> >
> > Here I would like to share the function I have prepared, for the
> > purpose to improve it.
> > Frankly, I am not clear about the exact meaning of some pixel format
> > (max, gdi, etc.) and I hope I  have put them under the right "case". I
> > have made only some superficial test and it seems to work.
> > Note that the purpose is to test ALPHA transparency (not transparency
> > in indexed-color image) this is useful because some programs do not
> > support it (as for instance IE 6)
> > I enclose all the source, included the handler for a button (button1)
> > on a form.
> >
> > The logic I use is to make first a "preliminary quick check", based on
> > the consideration that, if Alpha transparency is used, in the 95% of
> > the cases it "shows up" around the picture. If the check is
> > undeterminate, the user can specify to perform a full scan (this needs
> > to be improved much).
> >
> > Please, suggest all the code improvement that are useful to improve
> > this test and it's
> > speed ...
> >
> >
> > Imports System.Drawing.Imaging
> >
> > Public Class Form1
> >    Inherits System.Windows.Forms.Form
> >
> > #Region " Windows Form Designer generated code "
> > #End Region
> >
> >    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
> > System.EventArgs) Handles Button1.Click
> >
> >        'Dialog to load an image from disk
> >
> >        Dim FileImage As String
> >
> >        Dim Ofd As New OpenFileDialog
> >        With Ofd
> >            .Filter = "All files (*.*)|*.*" & _
> >                      "|Bitmap files (*.bmp)|*.bmp" & _
> >                      "|Portable Network Graphics files (*.png)|*.png"
> > & _
> >                      "|Jpeg files (*.jpg)|*.jpg" & _
> >                      "|Tiff files (*.tif)|*.tif" & _
> >                      "|GIF files (*.gif)|*.gif" & _
> >                      "|Windows Meta files (*.wmf)|*.wmf" & _
> >                      "|Windows Icon files (*.ico)|*.ico"
> >            If Not .ShowDialog.Equals(DialogResult.OK) Then Exit Sub
> >            FileImage = .FileName
> >            .Dispose()
> >        End With
> >
> >        Dim b As Bitmap
> >        Dim i As Image
> >
> >        Try
> >            i = Image.FromFile(FileImage)
> >        Catch ex As Exception
> >            MsgBox("Invalid picture or unsupported format")
> >            Exit Sub
> >        End Try
> >
> >        If TypeOf (i) Is Bitmap Then
> >            b = DirectCast(i, Bitmap)
> >            MsgBox("Uses Alpha transparency: " & _
> >                   Me.ImageUsesAlphaTransparency(b, True).ToString)
> >        Else
> >            MsgBox("Not a bitmap")
> >        End If
> >
> >    End Sub
> >
> >    Public Function ImageUsesAlphaTransparency(ByVal Bitmap As Bitmap,
> > _
> >                                               ByVal FullCheck As
> > Boolean) As Boolean
> >        With Bitmap
> >
> >            Select Case .PixelFormat
> >                Case PixelFormat.Indexed, _
> >                     PixelFormat.Format16bppGrayScale, _
> >                     PixelFormat.Format16bppRgb555, _
> >                     PixelFormat.Format16bppRgb565, _
> >                     PixelFormat.Format1bppIndexed, _
> >                     PixelFormat.Format24bppRgb, _
> >                     PixelFormat.Format32bppRgb, _
> >                     PixelFormat.Format48bppRgb, _
> >                     PixelFormat.Format4bppIndexed, _
> >                     PixelFormat.Format8bppIndexed, _
> >                     PixelFormat.Max  '(what's that?)
> >
> >                    Return False
> >
> >                Case PixelFormat.Format16bppArgb1555, _
> >                     PixelFormat.Format32bppArgb, _
> >                     PixelFormat.Format32bppPArgb, _
> >                     PixelFormat.Format64bppArgb, _
> >                     PixelFormat.Format64bppPArgb, _
> >                     PixelFormat.Gdi, _
> >                     PixelFormat.Alpha, _
> >                     PixelFormat.PAlpha, _
> >                     PixelFormat.DontCare, _
> >                     PixelFormat.Canonical, _
> >                     PixelFormat.Undefined, _
> >                     PixelFormat.Extended
> >
> >                    'Quick check of the 4 corners and center
> >                    '(as, usually, transparency is used around a
> > picture)
> >
> >                    If .GetPixel(0, 0).A < 255 Then Return True
> >                    If .GetPixel(Bitmap.Width - 1, Bitmap.Height - 1).A
> > < 255 Then Return True
> >                    If .GetPixel(0, Bitmap.Height - 1).A < 255 Then
> > Return True
> >                    If .GetPixel(Bitmap.Width - 1, 0).A < 255 Then
> > Return True
> >                    If .GetPixel(Bitmap.Width \ 2, Bitmap.Height \ 2).A
> > < 255 Then Return True
> >
> >                    'further checking needed (suggest code improvement)
> >
> >                    If FullCheck Then
> >                        For x As Integer = 0 To .Width - 1
> >                            For y As Integer = 0 To .Height - 1
> >                                If .GetPixel(x, y).A < 255 Then Return
> > True
> >                            Next y
> >                        Next x
> >                        Return False
> >                    Else
> >                        Return True 'conservative choice
> >                    End If
> >
> >                Case Else
> >                    MsgBox("Unexpected event")
> >                    Return True
> >
> >            End Select
> >
> >        End With
> >
> >    End Function
> >
> > End Class
> >
> >
> >
> >
> > -tommaso
> >

news:1149518891.569184.201390@i40g2000cwc.googlegroups.com...
> Yes Mick, you are right.
>
> I was aware of that, but frankly I am too unfamiliar with it to try to
> provide code useful for the community, and therefore, I was hoping that
> someone who has experience with it, would contribute it to enhance the
> scan part of the function.
>
> You mean this (Your code):
>
>    For y = 0 To bmData.Height - 1
>        For x = 0 To bmData.Width - 1
>            Dim PixelColor As Color
>            PixelColor = Color.FromArgb(Marshal.ReadInt32(bmData.Scan0,
> (bmData.Stride * y) + (4 * x)))
>            If PixelColor.A > 0 And PixelColor.A < 255 Then
>                IsAlphaBitmap = True
>                Exit For
>            End If
>        Next
>        If IsAlphaBitmap Then Exit For
>    Next
>
> right? But I am afraid this won't work with all PixelFormats listed
> under the "case" (?).
>
> When you do the merge, will you be as kind as to show your final code?
> I will be happy to collaborate, in case.
>
> There are still some obscure areas: like some PixelFormat (max, gdi). I
> am wondering what is "max" and if it should be moved in the "Alpha"
> case (?)
>
> -tom
>

> Yes that's the part that I meant. It obviously needs a little work for your
> requirements.
>
> You don't need to scan anything that does not support Alpha.
>
> The following is a list of ImageFormats that do support Alpha:
>     Format16bppArgb1555
>     Format32bppPArgb
>     Format64bppPArgb
>     Format32bppArgb
>     Format64bppArgb
>
> A simple test for this is:
>     Bitmap.IsAlphaPixelFormat(myBitmap.PixelFormat)
>
> You also need to know is the size of the scanbits. In my example it is 32
> since I am working with a 32bit argb bitmap, but this may not be the case in
> your image so you need to test it. A simple test is as follows:
>     Bitmap.GetPixelFormatSize(myBitmap.PixelFormat)
>
> Now we know the size of the scanbits for each pixel we know that we need to
> look at either 16, 32 or 64 bits at a time, and so know to use ReadInt16,
> ReadInt32 or ReadInt64 with the System.Runtime.InteropServices.Marshal class
>
> To improve slightly on my example for a 32 bit image, instead of converting
> to Color you can simply get the Alpha value directly from the Int32 value
> returned from Marshal.ReadInt32.
> i.e. instead of:
>     PixelColor = Color.FromArgb(Marshal.ReadInt32(bmData.Scan0, >
> (bmData.Stride * y) + (4 * x)))
>     If PixelColor.A > 0 AndAlso PixelColor.A < 255 Then
>
> you could use:
>     Alpha = Marshal.ReadInt32(bmData.Scan0, > (bmData.Stride * y) + (4 * x))
>  >> 24 And &HFF
>     If  Alpha > 0 AndAlso Alpha < 255 Then
>
>
> This is where it starts to get tricky, and I am no expert in this field. I
> did have a good MS reference for this when I was writing the method on my
> site, but I have misplaced it and so will have to look for it again. I
> wasn't really interested in any other formats at the time and so skipped
> over it and only extracted the info that was relevant to what I was doing.
>
> I seem to recall that there were some odd layouts and so you can't always
> rely on a ScanLine being layed out as for instance:
>
>   ARGBARGBARGBARGB
>
> because sometimes the Alpha channel is used as padding and so would result
> in:
>
>   RGBRGBRGBRGBAAAA
>
> ...but this may only have been for non Alpha ImageFormats.
>
> Whilst I am searching, the info on Bob Powell's site may be of some help,
> specifically the info on this page which I believe may have come from the
> same MS reference that I used:
> http://www.bobpowell.net/lockingbits.htm
>
> --
> Mick Doherty
> http://dotnetrix.co.uk/nothing.html
>
>
> <tommaso.gasta***@uniroma1.it> wrote in message
> news:1149518891.569184.201390@i40g2000cwc.googlegroups.com...
> > Yes Mick, you are right.
> >
> > I was aware of that, but frankly I am too unfamiliar with it to try to
> > provide code useful for the community, and therefore, I was hoping that
> > someone who has experience with it, would contribute it to enhance the
> > scan part of the function.
> >
> > You mean this (Your code):
> >
> >    For y = 0 To bmData.Height - 1
> >        For x = 0 To bmData.Width - 1
> >            Dim PixelColor As Color
> >            PixelColor = Color.FromArgb(Marshal.ReadInt32(bmData.Scan0,
> > (bmData.Stride * y) + (4 * x)))
> >            If PixelColor.A > 0 And PixelColor.A < 255 Then
> >                IsAlphaBitmap = True
> >                Exit For
> >            End If
> >        Next
> >        If IsAlphaBitmap Then Exit For
> >    Next
> >
> > right? But I am afraid this won't work with all PixelFormats listed
> > under the "case" (?).
> >
> > When you do the merge, will you be as kind as to show your final code?
> > I will be happy to collaborate, in case.
> >
> > There are still some obscure areas: like some PixelFormat (max, gdi). I
> > am wondering what is "max" and if it should be moved in the "Alpha"
> > case (?)
> >
> > -tom
> >

news:1149633968.344566.25160@u72g2000cwu.googlegroups.com...
> Very good Mick . Very interesting information.
>
> If the formats are only
>
>   Format16bppArgb1555
>    Format32bppPArgb
>    Format64bppPArgb
>    Format32bppArgb
>    Format64bppArgb
>
> I think we should have all the pieces of info to write the optimized
> function
> (Bob is reporting on his site the correspondent formula to adjust the
> addresses).
>
> I am just wondering about:
>
>                     PixelFormat.Max
>                     PixelFormat.Gdi
>                     PixelFormat.Alpha
>                     PixelFormat.PAlpha
>                     PixelFormat.DontCare
>                     PixelFormat.Canonical
>                     PixelFormat.Undefined
>                     PixelFormat.Extended
>
> what kind of images would fall into these categories ??
> Or perhaps are they meant for bitwise combination ? It's quite
> obscure...
>

> <tommaso.gasta***@uniroma1.it> wrote in message
> news:1149633968.344566.25160@u72g2000cwu.googlegroups.com...
> > Very good Mick . Very interesting information.
> >
> > If the formats are only
> >
> >   Format16bppArgb1555
> >    Format32bppPArgb
> >    Format64bppPArgb
> >    Format32bppArgb
> >    Format64bppArgb
> >
> > I think we should have all the pieces of info to write the optimized
> > function
> > (Bob is reporting on his site the correspondent formula to adjust the
> > addresses).
> >
> > I am just wondering about:
> >
> >                     PixelFormat.Max
> >                     PixelFormat.Gdi
> >                     PixelFormat.Alpha
> >                     PixelFormat.PAlpha
> >                     PixelFormat.DontCare
> >                     PixelFormat.Canonical
> >                     PixelFormat.Undefined
> >                     PixelFormat.Extended
> >
> > what kind of images would fall into these categories ??
> > Or perhaps are they meant for bitwise combination ? It's quite
> > obscure...
> >
>
> I believe these are just flags for the PixelFormat Enumeration and that no
> Image will actually return these values as the PixelFormat, but I couldn't
> say for certain.
>
> For example PixelFormat.32bppArgb would contain the PixelFormat.Alpha flag
> whereas PixelFormat.32bppPArgb would contain the PixelFormat.PAlpha flag.
>
> > Another doubt I have is why (in your code) the 0 value is excluded (no
> > color
> > contribution).
> >
>
> An Image may have been saved in a format that supports an Alpha Channel, but
> it may not actually have any Alpha Content. These Images will return 0 in
> the Alpha bit for Transparent Pixels and 255 for Solid Pixels and so could
> be classed as supporting Transparency rather than Alpha. If you're testing
> for Alpha content then it is very likely that it will be a value between On
> and Off.
>
> > In case you succeed putting all pieces toghether let me know your
> > result.
> > I am very interested in it.
> >
> > -tom
> >
> >
>
> I'm a bit busy at the moment, but if I come up with anything I'll post it
> here.
>
> --
> Mick Doherty
> http://dotnetrix.co.uk/nothing.html