Is there a reason why the gallery view of the images uses a set of images very roughly aligned with the break points but the lightbox view only uses the one image?
Also why don’t the gallery images take into account the number of columns in the layout? The page might be 1024px wide but if you are using a layout with more than one column then the images don’t really need to be 1200px.
Finally if my base image is 1024px wide and I have selected original as the lightbox max width then creating a 1200px wide version for the gallery is wasteful when it should just be using the original image (or something smaller).