As of today, DPL has no means other than export and comparing the source and exported images.
Lr uses a basically similar approach, with a fairly simple overlay and a low number of clicks needed…but Lr can easily show side-by side comparisons of any (two) images at any zoom ratio, a feature that is absent in DPL and that has been requested for a few years already.
DPL6’s current implementation to compare images is limited and more complicated to operate than desirable - as well as different on Win and Mac. But it’s nice to see that the lack of a feature has led @MSmithy to creative use.
- Limited to before/after: Works only for an input image and (one of) its output image(s)
But: no comparing of any two images. - Complicated: Select the input, go to the toolbar, select the image you want to compare, then click (one of the) compare button(s)…and while the two images can be compared…
the filmstrip does not show (or allow to select) the images that are being compared.