image manipulation in vb.net

Posted on 2006-05-25
Medium Priority
Last Modified: 2006-11-18

I need to get an image (jpeg or gif) resize it and then save it as a jpeg

I have seen various ways to do this on the internet and I have a few questions...

Most of the methods i have seen involve creating a bitmap object based on the original file and then manipulating it.

Can i create a bitmap object from both  gif and jepg?
Can i save a bitmap as both a gif and a jpeg?

How can i tell the file that I am resizing is actaully a valid jpg or gif or not something that has been wrongly named or something?

Also, how can i best maintain the image quality. I need to maintain the aspect ratio best as possible. Most examples i have seen let you specify the height and the width of the new image and then resize. I was thinking I could specify a maximum height and a maximum width and resize the image as best as possible within those maximum values.

Any advice much appreciated.

Thanks a lot
Question by:andieje
1 Comment

Accepted Solution

neilprice earned 2000 total points
ID: 16762305
This is some code to re-size a jpeg image:

        Dim factor As Double = 2.5
        Dim myImage As Bitmap = New System.Drawing.Bitmap("c:\\testimage.jpg")
        myImage = New Bitmap(myImage, New Size(myImage.Size.Width * factor, myImage.Size.Height * factor))
        myImage.Save("c:\\resized.jpg", System.Drawing.Imaging.ImageFormat.Jpeg)

When loading it (the second line) use a try catch block to catch exceptions, that way you'll know if you have something invalid trying to be loaded rather than an image.

You can create a bitmap from all the formats listed in System.Drawing.Imaging.ImageFormat I believe, and yes gif and jpg are both covered.

Hope this helps,

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