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如何获得jpg文件的实际尺寸呢？

来源：岁月联盟编辑：zhuzhu 时间：2003-07-11

网上找的一段代码，把它编译成组件就可以用了，还支持png 
 
 
'I have released this source code into the public domain.  You may use it 
'with no strings attached. 
'Just call GetImageSize with a string containing the filename, and 
'it will return a user defined type 'ImageSize'  (see below) 
'Return values of 0 indicate an error of some sort.  The error handling 
'in this module is limited.  There is *NO* error handling on the test 
'form.  This routine is limited to X or Y sizes of 32767 pixels, but that 
'should not be a problem. 
 
'Check back at http://www.qtm.net/~davidc 
'I may add support for more file types. 
 
'supported in this version: 
'JPEG 
'GIF 
'PNG 
 
'This routine does not require any royalty fees for Unisys as it 
'does nothing with the compressed part of GIF files.  It simply reads 
'4 bytes to determine image size. 
 
Option Explicit 
Public WImg As Long 
Public HImg As Long 
Public Type ImageSize 
    Width As Long 
    Height As Long 
End Type 
 
Public Sub GetImageSize(sFileName As String) 
    On Error Resume Next        'you'll want to change this 
    Dim iFN As Integer 
    Dim bTemp(3) As Byte 
    Dim lFlen As Long 
    Dim lPos As Long 
    Dim bHmsb As Byte 
    Dim bHlsb As Byte 
    Dim bWmsb As Byte 
    Dim bWlsb As Byte 
    Dim bBuf(7) As Byte 
    Dim bDone As Byte 
    Dim iCount As Integer 
 
    lFlen = FileLen(sFileName) 
    iFN = FreeFile 
    Open sFileName For Binary As iFN 
    Get #iFN, 1, bTemp() 
         
    'PNG file 
    If bTemp(0) = &H89 And bTemp(1) = &H50 And bTemp(2) = &H4E _ 
    And bTemp(3) = &H47 Then 
        Get #iFN, 19, bWmsb 
        Get #iFN, 20, bWlsb 
        Get #iFN, 23, bHmsb 
        Get #iFN, 24, bHlsb 
        'GetImageSize.Width = CombineBytes(bWlsb, bWmsb) 
        'GetImageSize.Height = CombineBytes(bHlsb, bHmsb) 
        WImg = CombineBytes(bWlsb, bWmsb) 
        HImg = CombineBytes(bHlsb, bHmsb) 
    End If 
     
    'GIF file 
    If bTemp(0) = &H47 And bTemp(1) = &H49 And bTemp(2) = &H46 _ 
    And bTemp(3) = &H38 Then 
        Get #iFN, 7, bWlsb 
        Get #iFN, 8, bWmsb 
        Get #iFN, 9, bHlsb 
        Get #iFN, 10, bHmsb 
        'GetImageSize.Width = CombineBytes(bWlsb, bWmsb) 
        'GetImageSize.Height = CombineBytes(bHlsb, bHmsb) 
        WImg = CombineBytes(bWlsb, bWmsb) 
        HImg = CombineBytes(bHlsb, bHmsb) 
    End If 
     
     
    'JPEG file 
    If bTemp(0) = &HFF And bTemp(1) = &HD8 And bTemp(2) = &HFF Then 
    Debug.Print "JPEG" 
        lPos = 3 
        Do 
            Do 
                Get #iFN, lPos, bBuf(1) 
                Get #iFN, lPos + 1, bBuf(2) 
                lPos = lPos + 1 
            Loop Until (bBuf(1) = &HFF And bBuf(2) <> &HFF) Or lPos > lFlen 
         
            For iCount = 0 To 7 
                Get #iFN, lPos + iCount, bBuf(iCount) 
            Next iCount 
            If bBuf(0) >= &HC0 And bBuf(0) <= &HC3 Then 
                bHmsb = bBuf(4) 
                bHlsb = bBuf(5) 
                bWmsb = bBuf(6) 
                bWlsb = bBuf(7) 
                bDone = 1 
            Else 
                lPos = lPos + (CombineBytes(bBuf(2), bBuf(1))) + 1 
            End If 
        Loop While lPos < lFlen And bDone = 0 
        'GetImageSize.Width = CombineBytes(bWlsb, bWmsb) 
        'GetImageSize.Height = CombineBytes(bHlsb, bHmsb) 
        WImg = CombineBytes(bWlsb, bWmsb) 
        HImg = CombineBytes(bHlsb, bHmsb) 
    End If 
    Close iFN 
     
End Sub 
Private Function CombineBytes(lsb As Byte, msb As Byte) As Long 
    CombineBytes = CLng(lsb + (msb * 256)) 
End Function