Let’s say I have some picture I want to use as my desktop wallpaper that has a 4:3 aspect ratio. My monitor, as one might expect these days, is 16:9. Cropping and/or zooming into the picture is the obvious solution, but in this case the subject would be awkwardly cropped. So, I’d like to mat or pillarbox the image in some way to make it look good (or at least better than the default teal of my desktop).
Are there any good guidelines or procedures for what looks best? I could imagine doing something like blurring and stretching the original and putting the picture on top of that, but I can’t get results I’m happy with. Should I change the saturation and/or value of the result? Is there some good algorithm that would tell me the best color to use? Twitter does something similar on their phone apps—should I try to copy what they do, which seems like most common color darkened and muted? Are there any apps or websites that do this?
(I hope all that made sense—I tried googling, but kept on getting hits for physical mats and wallpaper.)