Levels sets black, white, and midtone points; Curves offers more detailed control over tonal regions. Use both as Adjustment Layers to preserve the original image.
Read the histogram
The left represents shadows, the middle shows midtones, and the right represents highlights. Empty space is not automatically a defect. Clipping occurs when detail is forced into pure black or white.
Levels controls
| Control | Purpose |
|---|---|
| Black input | Sets the value that becomes black |
| Gray input | Adjusts midtone gamma |
| White input | Sets the value that becomes white |
| Output Levels | Limits output black and white |
Move input endpoints toward image data while holding Alt/Option to monitor clipping. Use the gray control for midtone brightness instead of forcing the endpoints.
Curves and the S-curve
The horizontal axis is input and the vertical axis is output. Drag upward to brighten and downward to darken. A gentle S-curve adds contrast; a reverse S reduces it. Keep control points sparse for smooth transitions.
Practical workflow
- Inspect the histogram and clipping.
- Use Levels for endpoints and a broad midtone correction.
- Use Curves for separate highlight, midtone, or shadow control.
- Restrict the effect with the Adjustment Layer mask.
- Reduce layer opacity if the result is too strong.
Common mistakes
- Crushing detail with aggressive endpoints.
- Adding too many curve points.
- Changing an RGB channel unintentionally.
- Judging tone in an overly bright room.
- Applying global contrast when only one area needs correction.
A histogram is a measurement, not an aesthetic formula. Use it to detect clipping and judge the image with your eyes.
Practice exercise
Edit one flat image with Levels and a second copy with Curves while keeping average brightness similar. Compare shadow detail, highlights, and midtone transitions.
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