change image dimensions

[kalos]

hello

I have a rectangular imagewith specific ratio, dpi, x dimension and y dimension

I want to preserve its dpi and ratio, but give its y dimension another value (which will alter x dimension proportionally, ofcourse)

how can I do this?

thanks!

[ewemoa]

I'm not sure about preserving DPI, but if it's scaling while preserving aspect ratio, one thing I might use is the GIMP's scale image feature:

  http://www.simplehelp.net/2007/08/13/how-to-resize-images-using-the-gimp/

[JavaJones]

This is a very common and simple image manipulation problem solved by most image editors, as far as I'm aware. So the better question is do you need to automate it, do it programatically, or batch-process, or something else complicated? Otherwise many applications should do what you want with a simple Resize function. For example XnView handles this easily. Just open the resize dialog, make sure it's set to preserve aspect ratio and *not* preserve print size (which would change DPI as you changed resolution), and then enter your new Y value, the X will adjust automatically. Note also that XnView has a batch processing function and I think there is even a commandline version and/or a library that you could access in code to do things programatically.

- Oshyan

[cmpm]

This one may be too simple, but it does have custom settings.
And claims to keep 'a proper aspect ratio'.
From their site.

FreeSizer will always use a proper aspect ratio, these values are not absolute. FreeSizer will automatically calculate the proper aspect ratio and use the values that are nearest to your desired image size.

http://freesizer.com/help/index.html?AdvancedResizingTechniques.html
http://www.freesizer.com/