Victor Image Processing Library How-to Tips

Load TIFF image from the Internet

To load an image from the Internet we use the Windows functions that give us access to remote files just like local files. Here's the sequence:

establish an Internet connection
acquire a handle to the remote file
determine the file size
allocate space in memory to hold the file
download the file to memory

After the file is in memory, we use the Victor Library functions to read the tiff information and extract the image data. That sequence is:

determine the image dimensions and pixel depth
allocate an image buffer to hold the image
load the image into the buffer

When the image is loaded it's then ready for display, processing, or saving to a local file

In this example we will load a 1-bit tiff with group 4 compression: www.catenary.com/howto/ibit.tif and display it in a VB picture box.

Load TIFF image from the Internet - the Visual Basic Source Code

Requires Victor Image Processing Library for 32-bit Windows v 5 or higher.


' ............................... Data Type Definitions .............................
Type imgdes
   ibuff As Long
   stx As Long
   sty As Long
   endx As Long
   endy As Long
   buffwidth As Long
   palette As Long
   colors As Long
   imgtype As Long
   bmh As Long
   hBitmap As Long
End Type

Type TiffData
   ByteOrder As Long
   width As Long
   Length As Long
   BitsPSample As Long
   comp As Long
   SamplesPPixel As Long
   PhotoInt As Long
   PlanarCfg As Long
   vbitcount As Long
End Type

' ............................... Function Declarations.............................
Declare Function tiffinfofrombuffer Lib "VIC32.DLL" (ByRef bytearray_firstelement As Byte, tdat As TiffData) As Long
Declare Function loadtiffrombuffer Lib "VIC32.DLL" (ByRef bytearray_firstelement As Byte, desimg As imgdes) As Long
Declare Sub freeimage Lib "VIC32.DLL" (image As imgdes)

Declare Function CreateCompatibleDC Lib "gdi32" (ByVal hdc As Long) As Long
Declare Function SelectObject Lib "gdi32" (ByVal hdc As Long, ByVal hObject As Long) As Long
Declare Function BitBlt Lib "gdi32" (ByVal hDestDC As Long, ByVal x As Long, ByVal y As Long, ByVal nWidth As Long, ByVal nHeight As Long, ByVal hSrcDC As Long, ByVal xSrc As Long, ByVal ySrc As Long, ByVal dwRop As Long) As Long

Public Declare Function InternetOpen Lib "wininet.dll" Alias "InternetOpenA" _ 
(ByVal sAgent As String, ByVal lAccessType As Long, ByVal sProxyName As String, _
ByVal sProxyBypass As String, ByVal lFlags As Long) As Long

Public Declare Function InternetOpenUrl Lib "wininet.dll" Alias "InternetOpenUrlA" _
(ByVal hOpen As Long, ByVal sUrl As String, ByVal sHeaders As String, _
ByVal lLength As Long, ByVal lFlags As Long, ByVal lContext As Long) As Long

Public Declare Function InternetReadFile Lib "wininet.dll" _
(ByVal hfile As Long, ByVal sBuffer As String, ByVal lNumBytesToRead As Long, _
ByRef lNumberOfBytesRead As Long) As Integer

Public Declare Function InternetReadBinaryFile Lib "wininet.dll" Alias "InternetReadFile" _
(ByVal hfile As Long, ByRef bytearray_firstelement As Byte, ByVal lNumBytesToRead As Long, _
ByRef lNumberOfBytesRead As Long) As Integer

Public Declare Function InternetCloseHandle Lib "wininet.dll" _
(ByVal hInet As Long) As Integer

Public Declare Function HttpQueryInfo Lib "wininet.dll" Alias "HttpQueryInfoA" (ByVal hOpen As Long, ByVal infotype As Long, _
ByVal buffer As String, ByRef bufferlength As Long, ByVal Index As Long) As Long

Global Const NO_ERROR = 0             ' No error
Public Const INTERNET_FLAG_RELOAD = &H80000000
Public Const INTERNET_OPEN_TYPE_PRECONFIG = 0


' ............................... The Function .............................
Private Sub mnuinet_Click()
Dim hOpen As Long
Dim hOpenUrl As Long
Dim rcode As Long
Dim retval As Long
Dim filesize As Long
Dim byteArray() As Byte
Dim tdat As TiffData
Dim timage As imgdes
Dim bufflen As Long
Dim databuff As String * 8
Dim bytesread As Long
Dim hMemDC As Long
Dim hOldBitmap As Long
Const SRCCOPY = &HCC0020

bufflen = Len(databuff)

hOpen = InternetOpen("Victor Library Sample", INTERNET_OPEN_TYPE_PRECONFIG, 0, 0, 0)
hOpenUrl = InternetOpenUrl(hOpen, "http://www.catenary.com/howto/1bit.tif", 0, 0, INTERNET_FLAG_RELOAD, 0)
If (hOpenUrl > 0) Then
    retval = HttpQueryInfo(hOpenUrl, 5, databuff, bufflen, 0) 'HTTP_QUERY_CONTENT_LENGTH (5) Retrieves the size of the resource, in bytes.

    If (retval > 0) Then
        filesize = databuff
        ReDim byteArray(filesize + 1) As Byte  ' Allocate space to hold the tiff file in memory
        retval = InternetReadBinaryFile(hOpenUrl, byteArray(0), filesize, bytesread)
        If (retval > 0) Then
            rcode = tiffinfofrombuffer(byteArray(0), tdat)
            If (rcode = NO_ERROR) Then
                rcode = allocimage(timage, tdat.width, tdat.length, tdat.vbitcount)
                If (rcode = NO_ERROR) Then
                    rcode = loadtiffrombuffer(byteArray(0), timage)
                End If
            End If
        End If
    End If

    InternetCloseHandle (hOpenUrl)
End If

If hOpen <> 0 Then InternetCloseHandle (hOpen)

' Use Picture1, a picture box control, to display the tiff image
hMemDC = CreateCompatibleDC(Picture1.hdc)
hOldBitmap = SelectObject(hMemDC, timage.hBitmap)
Picture1.width = tdat.width
Picture1.height = tdat.length
rcode = BitBlt(Picture1.hdc, 0, 0, tdat.width, tdat.length, hMemDC, 0, 0, SRCCOPY)
Picture1.Refresh

' Not shown here, but do clean up when you're done.
End Sub

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