ab Channels converts your photograph into CIE L*a*b* and lets you work the three channels separately. In RGB, brightness is baked into every channel. Turn down red and the picture gets darker as well as less red — the two cannot be separated. Lab splits them apart. One channel carries all the tone. Two carry all the colour: one running green to magenta, the other blue to yellow. That separation is the point. It lets you change colour without touching brightness, or brightness without shifting…

Sign in to see 30 days, 90 days and all history.