What to try
- In Levels, move Input black or Input white and probe a value in a flat segment.
- Switch to Curve and move its output at input 128; compare the curve and the image.
What to look for: The probe links one input to one output. Flat regions remove distinctions; steep regions expand them. The histogram shows how often source tones occur.
How it works
Levels sets input black and white points, a midtone gamma and output endpoints. Values below input black become output black; values above input white become output white. Moving the input endpoints inward stretches the remaining range and can increase contrast while clipping the tails.
Curves provides a more flexible mapping. The horizontal axis is input; the vertical axis is output. A point above the diagonal lightens that range, while a steeper section increases local contrast. The Lab composes a master curve with individual red, green and blue curves and shows a source histogram behind the graph.
Use it in the Lab
Use numeric point controls for precise changes and the graph for shaping. Preview on a selection when comparing a local treatment. Curves and their control points survive saved-chain replay in the Lab.
Limits & distinctions
A histogram shows how often values occur, not where they occur. Two very different compositions can have the same histogram.
Sources & references
Guide updated