High Quality Image Resizing

By changing interpolation mode (the algorithm used to resize) on a graphics object, you can resize your images and keep their quality.

It will use more cpu time then usual, that's why "nearest neighbour" is the traditionally used algorithm, as it is a low cpu cost method.

Here's is a function to resize your Images at a high quality

Code:

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    Private Function SizeImage(ByVal img As Bitmap, ByVal width As Integer, ByVal height As Integer) As Bitmap
        Dim newBit As New Bitmap(width, Height) 'new blank bitmap
        Dim g As Graphics = Graphics.FromImage(newBit)
        'change interpolation for reduction quality
        g.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic
        g.DrawImage(img, 0, 0, width, Height)
        Return newBit
    End Function

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Hi Phill,
This is a really handy code..:) really cool...Im gonna need to be able to zoom and stuff for one of my softwares you know about..Its gonna be quite useful to me atleast and also to tonnes of other people ;)
Keep coding....

Can you do it also with an image? in use of a bitmap

Bitmap is an inheritance of Image, so all you need to do is modify the header to input&output of type Image

Code:

---

Private Function SizeImage(ByVal img As Image, ByVal width As Integer, ByVal height As Integer) As Image

---

Can I take an image from the server and change the dimension with this function?

The function does not change the image dimension. I get no errors. Probably using the function wrong. Any ideas?

VB Code:

Sub UploadImage()
 
            Dim url As String = "/images/artikkelBilder/"
            Dim bildeTeller As Integer = 0
 
            If Not (fileupload1.PostedFile Is Nothing) Then 'Is there something to upload?
 
 
 
                Dim strLongFilePath As String = fileupload1.PostedFile.FileName
                Dim intFileNameLength As Integer = InStr(1, StrReverse(strLongFilePath), "\")
                Dim strFileName As String
 
 
                If intFileNameLength > 0 Then
                    strFileName = Mid(strLongFilePath, (Len(strLongFilePath) - intFileNameLength) + 2)
                Else
                    strFileName = strLongFilePath
                End If
 
                Select Case fileupload1.PostedFile.ContentType
                    Case "image/pjpeg", "image/jpeg", "image/png", "image/gif"  'Valid file?
                        fileupload1.PostedFile.SaveAs(Server.MapPath(url) & strFileName)
                        Dim bilde As Image = Image.FromFile(Server.MapPath(url) & strFileName)
                        SizeImage(bilde, 150, 100)
                        lbStatus.Text += "Image path: " & "http://www.dyrebeskyttelsenhordaland.ord/images/artikkelBilder/" & strFileName & "<br>"
                    Case Else
                        'Not valid file
                        lbStatus.Text += "Ugyldig bildeformat! <br>"
                End Select
            End If
 
        End Sub
 
        Private Function SizeImage(ByVal img As Image, ByVal width As Integer, ByVal height As Integer) As Image
            Dim newBit As New Bitmap(width, height) 'new blank bitmap
            Dim g As Graphics = Graphics.FromImage(newBit)
            'change interpolation for reduction quality
            g.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic
            g.DrawImage(img, 0, 0, width, height)
            Return newBit
        End Function
 
    End Class

I think you were under the assumption it is a sub which takes an object reference and simply changes your image. Infact it is a functon which accept your image & dimension and RETURNS a new image.

so you should change this line

VB Code:

SizeImage(bilde, 150, 100)

To

VB Code:

bilde = SizeImage(bilde, 150, 100)

Thanks for quick reply.
It did'nt work, no difference.

After it returns the new image, i'm supposed to save it again on the server?

if you want it changed on the file, yes.
You will have to dispose the original image to do this otherwise you will get access errors

Code:

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Dim temp As Bitmap = SizeImage(bilde, 150, 100)
bilde.dispose
bilde = temp
bilde.Save(filename)

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Thanks Phill64, worked like a charm :)

One more question :)

I want the last added picture to be deleted if the user uploads a new one.

Looks like it does'nt go through the IF, here is the code:
http://pastebin.com/578210

Solved it, had to use try catch and session :)