Question on Sight image size (Resolved)

I'm trying to build a banner-like image across either 3/4 or the full width of the screen.

The height will be some small portion (1/4 or much less) of the width.

Is there an algorithm I can use to determine canvas size of the image I'm using?

I don't want to spend much more time with trial and error on what is likely to be mostly a cosmetic feature. All attempts so far have been unsuccessful. Too much white space and aspect ratio.

Thanks.

Update:

I have a work-around for now. 

I opened the Sight in edit mode and created a blank widget of the size I wanted.

I then used a screen capture tool to grab the area in the exact size I wanted.

I used this as the basis for the canvas size and while there is still a bit of white space (since i can't reproduce the original size exactly), it is likely only noticable to me.

Craig