Using Active Server Pages (ASP), you can view images stored
in BLOB (Binary Large Object) fields in your Internet browser. This article
provides information on how to display a GIF image stored in the Microsoft SQL
Server sample database table pub_info.
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Most Internet browsers support the displaying of GIF and
JPEG images. To display an image, the browser requests the image from a Web
server. The server passes the image to the browser as an HTTP transaction with
an HTTP header containing an MIME type of IMAGE/GIF or IMAGE/JPEG. You can
simulate this behavior with Active Server Pages.
The following
example constructs an HTTP header for an image and then uses the binary
information from an image field in SQL Server to provide a GIF to the browser.
FILE: SHOWIMG.ASP
<%@ LANGUAGE="VBSCRIPT" %>
<%
' Clear out the existing HTTP header information
Response.Expires = 0
Response.Buffer = TRUE
Response.Clear
' Change the HTTP header to reflect that an image is being passed.
Response.ContentType = "image/gif"
Set cn = Server.CreateObject("ADODB.Connection")
' The following open line assumes you have set up a System DataSource
' by the name of myDSN.
'Remember to change the following connection string parameters to reflect the correct values
'for your SQL server.
cn.Open "DSN=myDSN;UID=<username>;PWD=<strong password>;DATABASE=pubs"
Set rs = cn.Execute("SELECT logo FROM pub_info WHERE pub_id='0736'")
Response.BinaryWrite rs("logo")
Response.End
%>
This script only displays an image on the screen. If you wish to
display an image from an HTML or ASP document you must refer to this script in
an image tag. For example, if you wished to display this image with a caption
describing it, you might use the following HTML page:
<HTML>
<HEAD><TITLE>Display Image</TITLE></HEAD>
<BODY>
This page will display the image New Moon Books from a SQL Server
image field.<BR>
<IMG SRC="SHOWIMG.ASP">
</BODY>
</HTML>
The ASP script assumes that the image field (BLOB Data) in the
SQL Server table contains a raw GIF image. Internet browsers assume that raw
GIF or JPEG data follow the HTTP header. If any extraneous information is
contained in the
BLOB data, this will be passed by this script, and the image will not
display properly. This becomes important when you realize that most methods of
placing images into
BLOB fields place extra information in the form of headers with the
image. Examples of this are Microsoft Access and Microsoft Visual FoxPro. Both
of these applications save OLE headers in the
BLOB field along with the actual binary data.
This
technique can also be applied to other types of binary data, not just graphics.
The browser needs to know what type of content is being presented. Do this by
specifying the proper mime type in the Response.ContentType variable. For
example, if you wanted to view a word document, you would set the ContentType =
"application/msword".
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For the latest Knowledge Base artices and other support
information on Visual InterDev and Active Server Pages, see the following page
on the Microsoft Technical Support site:
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