Slide Show project - image smaller than window

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First off - this is my first venture into image processing, and I'm so glad that I found cv!

I'm developing something of a slide show program, and have gotten cv to display an image and that image size properly based on the secondary display.

I'm curious though, about the best method to tackle my next problem... If the image is smaller has a different aspect ratio than the screen, I'd like it to be displayed with the correct ratio, but on a black background.

I'm wondering if I'm overlooking some simple method of doing this? Or will I need to dynamically create an image with the black background and then copy the loaded image to that.

Any help or sample code would be appreciated. Thanks in advance!