Camera image size

I am writing a Cocoa application for mac osx. I'm trying to figure out how to determine the size of an image that will be captured by a camera? I would like to know the size of the image that will be captured so I can setup a view with an aspect ratio that won't distort the image. For example, if my view is defined to be 640x360 and my camera captures images that are 640x480, the displayed image looks sh开发者_如何学编程ort and fat. I'm also displaying some other layers over the image and I need the image size to be able to scale and position the layers properly.

I won't know the type of camera that is attached until run-time so I'd like to be able to interrogate the device and get attributes like image size. Thanks for the help...

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You are altering the aspect ratio of the image when you capture in 640x360 instead of 640x480 or 320x240. You are doing something similar as a resize, using the whole image and making it a different size.

If you don't want to distort the image, but use only a portion of it you need to do a crop. Some hardware support cropping, others don't and you have to do it in software. Cropping is using only portions of the original image. In your case, you would discard the bottom 120 lines.

Example (from here):

The blue rectangle is the natural, or original image and the red is a crop of it.