I don’t know how it could do this very effectively… As far as I know there is no tangible relationship between image size and interval.
Saying that, when using a preprocessed image, such as from Imag-R, there is a need for Lightburn to know the interval. We normally think of resolution across the X axes, but it applies to both axes. Since interval is not accessible when pass though is enabled, Lightburn needs to know the interval to step the Y axes the proper amount… I’m speculating here, but it seems to fit…
This thread discusses it… maybe this is where you saw that image size determines dpi. Always possible that I didn’t read it correctly 
I don’t know how this works internally… but I know if I have to execute more code, it takes time… I wouldn’t think just passing a threshold image would slow it down. This happens so fast anyway…
