Read JPG Header Comment (VB6)

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I found this code in Google, used to read header info from a JPG.
I am hoping this code will return any comments added.
My hope is to have some kind of marker next to the image to show the user there are comments attached to the image.
Can some-one help to explain how to use this code, do I need some kind of text control to show the info etc.

  Public Type BITMAPINFO
    Width             As Long
    Height            As Long
  End Type

  Public Function GetJPGInfo(ByVal FileName As String) As BITMAPINFO
    Dim bChar As Byte
    Dim a As Byte, b As Byte
    Dim c As Byte, D As Byte
    Dim E As Byte, f As Byte
    Dim i As Integer
    Dim DotPos As Integer
    Dim Header As String
    Dim blExit As Boolean
    Dim MarkerLen As Long
    Dim ImgWidth As Integer
    Dim ImgHeight As Integer
    Dim ImgSize As String
    Dim fnum As Integer
    Dim ImageInfo As BITMAPINFO
    On Error Resume Next
    
    fnum = FreeFile
    Open FileName For Binary As #fnum

    ImgSize = LOF(fnum) / 1024
    DotPos = InStr(ImgSize, ",")
    ImgSize = Left(ImgSize, DotPos)

    Get #fnum, , bChar
    Header = Hex$(bChar)
    Get #fnum, , bChar
    Header = Header & Hex$(bChar)
    If Header  "FFD8" Then Exit Function

    While Not blExit
        Do Until Hex$(bChar) = "FF"
           Get #fnum, , bChar
        Loop

        Get #fnum, , bChar
        If Hex$(bChar) >= "C0" And _
             Hex$(bChar) <= "C3" Then
           Get #fnum, , bChar
           Get #fnum, , bChar
           Get #fnum, , bChar

           Get #fnum, , bChar
           a = bChar
           Get #fnum, , bChar
           b = bChar
           Get #fnum, , bChar
           c = bChar
           Get #fnum, , bChar
           D = bChar

           ImgHeight = CInt(a * 256 + 
           ImgWidth = CInt(c * 256 + D)
           blExit = True
        Else
           If Hex$(bChar) = "DA" Then
              blExit = True
           Else
              Get #fnum, , bChar
              E = bChar
              Get #fnum, , bChar
              f = bChar
              MarkerLen = (E * 256 + f) - 2
    
              Dim marker As String
              marker = String(MarkerLen, vbNullChar)
              Get #fnum, , marker
           End If
        End If
    Wend

    Close #fnum

    With ImageInfo
         .Width = ImgWidth
         .Height = ImgHeight
    End With
    
    GetJPGInfo = ImageInfo
End Function

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The code you posted will retrieve the height and width of a .jpg file. I don’t know anything about the way comments are stored inside the header of a .jpg file, so I can’t tell you how to get at the comment. Does the software you use for adding the comments allow you to retrieve them?

The code in your post can be used like this:

– Put text boxes txtFilename, txtHeight and txtWidth on a form.
– Put a command button cmdGetInfo on the form.
– In the On Click event of the command button, retrieve height and width of the .jpg whose name is in txtFilename.
– Put the result in the other text boxes.

Private Sub cmdGetInfo_Click()
Dim bi As BITMAPINFO
bi = GetJPGInfo(txtFilename)
txtHeight = bi.Height
txtWidth = bi.Width
End Sub

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Hans
The software is very limited “edJpgCom.exe” but very useful to say the least.
On double clicking the image (as visited earlier) the user is able to add a comment to the header.
The image is then saved with new header information and over-writes the image.
The only draw back, there’s no visual way to show the user that there is a comment attached other than double clicking each image.
If I could access this comment information, I’m sure I could build something into the array to perhaps show an icon of some sort next to
the image.

I’ll try your suggestion anyway and play with the modul to see if there is any other info which can be accessed.

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Dave,

I found some info about the way comments are stored. Could you attach a small .jpg that contains comments? That would allow me (and others) to experiment. Thanks in advance.

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Hans
No problem at all

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Is the comment “image33” ?

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Here you go. Oliver Fromme from Germany has written a clear description of the JPG header structure; you can find it (for example) here. With this description, it wasn’t hard to adapt the code you posted to return the comment instead of the height and width. The new code is attached in a text file

Use as follows:

txtComment = GetJPGComment(txtFilename)

where txtFilename is a text box containing the full path and filename of a .JPG file, and txtComment a text box to display the comment.

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Hans
You just love a challenge ??

I think I can use this now to show an icon next to the pic (excuse typo)

Dim i as integer

If Me.Controls("txtComment" & i).Text = vbNullString Then
Me.Icon? .Visible = False
Else
Me.Icon?.Visible = True

I’ll try to build something into the FillImages Array using the “For” and “Next” statements.
When the user see’s the icon, he knows there is a comment attached.

What do you think ?

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You could put a series of icons on the form, named Icon1, Icon2, etc., and refer to them as Me.Controls(“Icon” & i)
Alternatively, you could use check boxes chkComment1, chkComment2, etc.

If Me.Controls(“txtComment” & i).Text = vbNullString Then
Me.Controls(“chkComment” & i) = 0
Else
Me.Controls(“chkComment” & i) = 1
End If

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Where to trim from ?

I’ve tried a couple of combinations, but nothing but the delete button works:

Me.Controls(“txtComment” & i).Text = GetJPGComment(Trim$(“L:mmpdfimage” & (Left$(arrFileNames(i + intIndex – 1, 1), 8) & “.jpg”)))
::
Me.Controls(“txtComment” & i).Text = (Trim$GetJPGComment(“L:mmpdfimage” & (Left$(arrFileNames(i + intIndex – 1, 1), 8) & “.jpg”)))
::

Dim TrStr as String

For E = 1 To intNumberOfImages
TrStr = Me.Controls(Trim$(“txtComment” & E)).Text
If Me.Controls(TrStr).Text = vbNullString Then
Me.Controls(“check” & E).Visible = False
Else
Me.Controls(“check” & E).Visible = True
End If
Next

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In the first part, you want to trim the comment, not the file name:

Me.Controls(“txtComment” & i).Text = Trim$(GetJPGComment(“L:mmpdfimage” & Left$(arrFileNames(i + intIndex – 1, 1), 8) & “.jpg”))

In the second part, you want to trim the text in the control, not the name of the control:

TrStr = Trim$(Me.Controls(“txtComment” & E).Text)
If TrStr = vbNullString Then
…

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Hans
I knew I wasn’t far off:

Me.Controls(“txtComment” & i).Text = Trim$(GetJPGComment(“L:mmpdfimage” & Left$(arrFileNames(i + intIndex – 1, 1), 8) & “.jpg”))

Perhaps I was looking too far.

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Hans
I knew I wasn’t far off:

Me.Controls(“txtComment” & i).Text = Trim$(GetJPGComment(“L:mmpdfimage” & Left$(arrFileNames(i + intIndex – 1, 1), 8) & “.jpg”))

Perhaps I was looking too far.

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Hans

One of the guys has had a new camera and I think the make up of the image or header is structured differently.
Attached are two images:

81111.17 (Taken with new camera)

81111.21 (Taken with old camera)

Both have comments in the headers but the image taken with the new camera doesn’t populate the (“txtComment” & i) control ?
Therefore not allowing the marker to tell the user there is a comment attached..
Is it possible to edit the code to rectify this ?

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The images ( Sorry I can’t get image 2 under 100k, sent to gmail instead)]

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The attached version of the code correctly extracts the comment from all JPG images I could find that have one, but there is a risk that it returns an incorrect value. Test it on a series of images to see if it works for you

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The code I originally posted higher up in this thread skips over segments of the jpg file that don’t have a comment header. However, in the new sample picture provided by Dave, the comment segment is buried within another segment with a different header, so if you skip segments, you won’t find the comment. The code attached to my previous reply simply trudges through the file until a comment header is found, but this is painfully slow.
I found a class module that looked promising, but it couldn’t handle large picture files, and what’s worse, it didn’t find *any* comments

If somebody knows of efficient code or perhaps a DLL (preferably free) that can retrieve the comment from any jpg file, please post a reply. Thanks in advance.

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In the first part, you want to trim the comment, not the file name:

Me.Controls(“txtComment” & i).Text = Trim$(GetJPGComment(“L:mmpdfimage” & Left$(arrFileNames(i + intIndex – 1, 1), 8) & “.jpg”))

In the second part, you want to trim the text in the control, not the name of the control:

TrStr = Trim$(Me.Controls(“txtComment” & E).Text)
If TrStr = vbNullString Then
…

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Where to trim from ?

I’ve tried a couple of combinations, but nothing but the delete button works:

Me.Controls(“txtComment” & i).Text = GetJPGComment(Trim$(“L:mmpdfimage” & (Left$(arrFileNames(i + intIndex – 1, 1), 8) & “.jpg”)))
::
Me.Controls(“txtComment” & i).Text = (Trim$GetJPGComment(“L:mmpdfimage” & (Left$(arrFileNames(i + intIndex – 1, 1), 8) & “.jpg”)))
::

Dim TrStr as String

For E = 1 To intNumberOfImages
TrStr = Me.Controls(Trim$(“txtComment” & E)).Text
If Me.Controls(TrStr).Text = vbNullString Then
Me.Controls(“check” & E).Visible = False
Else
Me.Controls(“check” & E).Visible = True
End If
Next

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You could put a series of icons on the form, named Icon1, Icon2, etc., and refer to them as Me.Controls(“Icon” & i)
Alternatively, you could use check boxes chkComment1, chkComment2, etc.

If Me.Controls(“txtComment” & i).Text = vbNullString Then
Me.Controls(“chkComment” & i) = 0
Else
Me.Controls(“chkComment” & i) = 1
End If

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Not that you need another method, but I stumbled across this the other day and managed to find it again: Retrieving Extended File Properties from Windows 2000 Scripting Guide on MSDN. I wonder whether the Comments field matches up with the internal Comments field in the JPG file?

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Thanks all for the extended contribution and information.
(Sorry I couldn’t reply late yesterday, connection problems here and couldn’t log on to the site ( Server Re-Boot sorted it))

I have the application running now as I wanted it to.
By checking the string of hidden controls, I can now show an icon for each image with a comment:

(From FillImages Function)
Me.Controls("txtComment" & i).Text = GetJPGComment("L:mmpdfimage" & _
 (Left$(arrFileNames(i + intIndex - 1, 1), 8) & ".jpg"))
 
Dim E as Integer
For E = 1 To intNumberOfImages
        If Me.Controls ("txtComment" & E).Text = vbNullString Then
        Me.Controls("check" & E).Visible = False
    Else
        Me.Controls("check" & E).Visible = True
    End If
    Next

All I have to do now is to trim spaces from the txtComment text box’s to make the automation more efficient.
Again, Thanks all:

Reply | Quote

Thanks all for the extended contribution and information.
(Sorry I couldn’t reply late yesterday, connection problems here and couldn’t log on to the site ( Server Re-Boot sorted it))

I have the application running now as I wanted it to.
By checking the string of hidden controls, I can now show an icon for each image with a comment:

(From FillImages Function)
Me.Controls("txtComment" & i).Text = GetJPGComment("L:mmpdfimage" & _
 (Left$(arrFileNames(i + intIndex - 1, 1), 8) & ".jpg"))
 
Dim E as Integer
For E = 1 To intNumberOfImages
        If Me.Controls ("txtComment" & E).Text = vbNullString Then
        Me.Controls("check" & E).Visible = False
    Else
        Me.Controls("check" & E).Visible = True
    End If
    Next

All I have to do now is to trim spaces from the txtComment text box’s to make the automation more efficient.
Again, Thanks all:

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The URL for the article “Retrieving Extended File Properties” has changed to http://www.microsoft.com/technet/scriptcen…s_fil_lunl.mspx%5B/url%5D.

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Not that you need another method, but I stumbled across this the other day and managed to find it again: Retrieving Extended File Properties from Windows 2000 Scripting Guide on MSDN. I wonder whether the Comments field matches up with the internal Comments field in the JPG file?

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Edited – Added graphic to try to make this clearer

Jumping late here (as usual) with some information I dug out from an old post I made to somebody:
“I have had cause to dig into the JPEG internal format & header information (to extract the metrics actually) but recall the existence of a well defined internal comment field. If this is the “comment” you’re referring to, then I can’t see why the task you describe would be hard at all (to program).

JPEGs are full of markers, prefixed by FF (hexadecimal). Comment marker is identifiable as FFFE

The first two bytes, the length, after the FF marker indicate the number of bytes, including the two length bytes, that this header contains. The next bytes contain whatever the user wants to use as a comment.”

This might help as a summary of the relevant information. The full standard can be viewed here. You (generic) can get a good idea of the way the JPEG markers work by viewing one in a hex editor but I see you’ve already zeroed in on it Hans . I may “lift” your code for future reference.

Alan

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Edited – Added graphic to try to make this clearer

Jumping late here (as usual) with some information I dug out from an old post I made to somebody:
“I have had cause to dig into the JPEG internal format & header information (to extract the metrics actually) but recall the existence of a well defined internal comment field. If this is the “comment” you’re referring to, then I can’t see why the task you describe would be hard at all (to program).

JPEGs are full of markers, prefixed by FF (hexadecimal). Comment marker is identifiable as FFFE

The first two bytes, the length, after the FF marker indicate the number of bytes, including the two length bytes, that this header contains. The next bytes contain whatever the user wants to use as a comment.”

This might help as a summary of the relevant information. The full standard can be viewed here. You (generic) can get a good idea of the way the JPEG markers work by viewing one in a hex editor but I see you’ve already zeroed in on it Hans . I may “lift” your code for future reference.

Alan

Reply | Quote

Here you go. Oliver Fromme from Germany has written a clear description of the JPG header structure; you can find it (for example) here. With this description, it wasn’t hard to adapt the code you posted to return the comment instead of the height and width. The new code is attached in a text file

Use as follows:

txtComment = GetJPGComment(txtFilename)

where txtFilename is a text box containing the full path and filename of a .JPG file, and txtComment a text box to display the comment.

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Is the comment “image33” ?

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Hans
No problem at all

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Dave,

I found some info about the way comments are stored. Could you attach a small .jpg that contains comments? That would allow me (and others) to experiment. Thanks in advance.

Reply | Quote

Hans
The software is very limited “edJpgCom.exe” but very useful to say the least.
On double clicking the image (as visited earlier) the user is able to add a comment to the header.
The image is then saved with new header information and over-writes the image.
The only draw back, there’s no visual way to show the user that there is a comment attached other than double clicking each image.
If I could access this comment information, I’m sure I could build something into the array to perhaps show an icon of some sort next to
the image.

I’ll try your suggestion anyway and play with the modul to see if there is any other info which can be accessed.

Reply | Quote

The code you posted will retrieve the height and width of a .jpg file. I don’t know anything about the way comments are stored inside the header of a .jpg file, so I can’t tell you how to get at the comment. Does the software you use for adding the comments allow you to retrieve them?

The code in your post can be used like this:

– Put text boxes txtFilename, txtHeight and txtWidth on a form.
– Put a command button cmdGetInfo on the form.
– In the On Click event of the command button, retrieve height and width of the .jpg whose name is in txtFilename.
– Put the result in the other text boxes.

Private Sub cmdGetInfo_Click()
Dim bi As BITMAPINFO
bi = GetJPGInfo(txtFilename)
txtHeight = bi.Height
txtWidth = bi.Width
End Sub

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