It is helpful while you work to be able to compare the image before and after you’ve made changes to see what you like best. To do this dynamically, just put a checkmark in the Show original image box and a small white knob will appear in the middle of the picture. Drag the knob left and right to compare. The right side will show the original image (excluding cropping) and the left side will show the enhanced image. To erase the effects, go to the Gear button and choose Undo all filters.