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Binary streaming of large images from Database

, 29 Jun 2004
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Explains how to perform drawing on a large image retrieved from the database, and then stream the image with the "Open/Save" option.

Introduction

This explains how to perform drawing operations on a large image retrieved from the database, and then stream the image on the browser, with the "Open/Save" option.

Getting the Image from Database

For this sample code, I have a database table ImageTable which contains a column Image of data type image.

First, we need to fetch the image from the database. Since we need to do some drawing on the image, we convert the image into a System.Drawing.Image. The function below converts the image bytes into the System.Drawing.Image and returns it.

' This function returns the image retrieved from the database
Private Function GetImageFromDB(ByVal ImageID As Integer) As Image    
    Dim image As Image
    ...
    ...

    Try
        sqlCommand = "SELECT Image FROM ImageTable WHERE ImageID = "_
                     + ImageID.ToString()
        
        ...
               
        Dim dr As SqlDataReader
        dr = cmd.ExecuteReader()
        While (dr.Read())

            Dim byt As Byte()
            byt = dr.Item(strImage)
            ' Convert the image bytes to System.Drawing.Image
            Dim bmp As New Bitmap(New System.IO.MemoryStream(byt))
            image = bmp
                    
        End While
    
    ...
    
    End Try

    Return image

End Function

Now, we have to use this image and perform drawing operations on the image, and then stream it as a binary output to the browser. The image is retrieved as:

Dim image As Image
image = GetImageFromDB(ImageID)

Getting a Graphics object

In order to perform drawing operations on the image, we have to use the System.Drawing.Graphics class. You can get the Graphics object directly from the database image if it is not in Indexed Pixel Format. For images with Indexed Pixel Format, we can get the Graphics object by creating a temporary bitmap and then copying the database image onto the bitmap. The code to do this is shown below:

Dim bmpNew As Bitmap
Dim imageNew As Image
Dim objGraphics As Graphics
Try
    objGraphics = Graphics.FromImage(image)               

Catch e As Exception
    ' The image is in indexed pixel format
    ' Create a temp bitmap

    bmpNew = New Bitmap(image.Width, image.Height)
    imageNew = bmpNew

    objGraphics = Graphics.FromImage(imageNew)

    ' Draw the contents of old bitmap to new bitmap
    objGraphics.DrawImage(image, New Rectangle(0, 0, _
                          imageNew.Width, imageNew.Height), _
                          0, 0, image.Width, image.Height, _
                          GraphicsUnit.Pixel)

    image = imageNew

End Try

Drawing on the image

That would retrieve the image from the database and create a Graphics object. Now, perform all the drawing you need to do on the Graphics object. Let's say, write a simple text over the image..

Dim objFont As Font = New Font("Verdana", 12, FontStyle.Bold)
Dim objbrush As Brush = Brushes.Black
Dim rect As New Drawing.RectangleF(10, 10, 200, 50)
Dim objGraphics As Graphics
objGraphics.DrawString("Simple Text", objFont, objbrush, rect)

Binary Streaming

Once we are done with the drawing operations on the image, we stream it to the browser. A simple image.Save(Response.OutputStream, ImageFormat.Jpeg) would have been sufficient for small image files. For large files (say over 1 MB), the image should be streamed in chunks of fixed size.

' Set the content type
Response.ContentType = "image/Jpeg"

Dim ms As MemoryStream = New MemoryStream()
image.Save(ms, Imaging.ImageFormat.Jpeg)
Dim bytImage(ms.Length) As Byte
bytImage = ms.ToArray()
ms.Close()

ms = New MemoryStream(bytImage)
Response.Clear()
Response.AddHeader("Content-Type", "binary/octet-stream")
Response.AddHeader("Content-Length", bytImage.Length.ToString())
Response.AddHeader("Content-Disposition", _
     "attachment; filename=DownloadedImage.jpg; size=" _
     + bytImage.Length.ToString())
Response.Flush()

Dim chunkSize As Integer = 1024

Dim i As Integer
For i = 0 To bytImage.Length Step chunkSize
    ' Everytime check to see if the browser is still connected
    If (Not Response.IsClientConnected) Then
        Exit For
    End If

    Dim size As Integer = chunkSize
    If (i + chunkSize >= bytImage.Length) Then
        size = (bytImage.Length - i)
    End If

    Dim chunk(size - 1) As Byte
    ms.Read(chunk, 0, size)
    Response.BinaryWrite(chunk)
    Response.Flush()
Next
ms.Close()

In this case, I read the bytes and stream them in sizes of 1024. The above code will ultimately throw a "file download" dialog with the "open/save" option, and the user can either open the image from the location or save it to his disk. This is achieved using the lines:

Response.AddHeader("Content-Type", "binary/octet-stream")
Response.AddHeader("Content-Disposition", _
  "attachment; filename=DownloadedImage.jpg; size=" _
  + bytImage.Length.ToString())

Without these lines, the image would be streamed directly to the client and will show up in the browser.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Tingz Abraham

United States United States
When Tingz Abraham was old enough to realize that computers were going to invade the world, he decided to pursue a career that would keep him close to computers. That landed him a job as an IT Solutions Consultant in Seattle, USA where he currently works. He believes he can program in many languages, including English. Ctrl+C and Ctrl+V are his favorite keys on the keyboard.
 
After he found he sucked real bad at playing the violin, he just stuck to the guitar and piano. He has a ravishing need for speed and takes a fancy to anything with wheels, including his black Mustang which he's aptly named 'Tingzmobile'.
 
At work you can constantly hear him say - "Oh! The things I learn after I know it all!" He keeps himself very busy, and in his spare time he keeps wondering why '24 hours a day is just not enough'.
 
He exists at www.Tingzabraham.com

Comments and Discussions

 
General[My vote of 2] error PinmemberMohan19845-Aug-10 21:18 
Generalmemory problems with large images PinmemberNasenbaaer29-Mar-07 11:57 
Hi
 
I just wanted to manipulate these Bytes in memory to calculate some new colors. But my problem is, in my Pocket PC with 32MB memory, the system crashes by doing a everless loop. Then my program does not response anymore. You can test this effect by just making a Button in a Form and doing the following:
 
Dim MyArray() As Byte
Redim MyArray(5000000) 'About 5MB
This is just for testing. But there are 14MB free and I dont know why it could not allocate my 5MB.
 
Please help, by just putting the code above in a new cf.net project and using the PPC 2003 emulator with 32MB ram. And telling me if you have the same effect and how to solve it.
 

Need help
Timo
GeneralDifferent Content-Types of images Pinmemberfdelagarza21-Sep-06 6:31 
GeneralImage details PinmemberMsuk11-Jul-06 5:54 
GeneralA little more efficient for streaming PinmemberNathan Blomquist30-Jun-04 18:01 
GeneralRe: A little more efficient for streaming PinmemberTiNgZ aBrAhAm30-Jun-04 18:22 

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