Some times in Photoshop I will use a color checker card and use the eye droppers in the curves adjustment layer to click on black, gray, and white swatches. Am I missing something or does Lightroom not have a way to do this with its tone curve module? Maybe it doesn't make sense to do this in LR but it seems like it would be handy, I could 'correct' many photos at once without going to Photoshop.