Tonkurvor

Tonkurvor, or tone curves, are a graphical adjustment tool used in digital photography and image processing to remap luminance values. They allow precise control over how input brightness levels are translated into output brightness, enabling nuanced tonal edits beyond simple brightness or contrast sliders.

The curve is plotted with input brightness on the horizontal axis and output brightness on the vertical axis. The baseline diagonal represents a direct, unchanged mapping. By adding and moving control points, editors reshape the curve to compress or expand tonal ranges, modify highlights and shadows, and shift midtones. Endpoints typically anchor the darkest and lightest tones, preserving black and white points while the curve alters tonal relationships in between.

Common curve shapes include linear, which yields no change, and S-curves, which increase overall contrast by darkening shadows and brightening highlights while affecting midtones. Adjustments can be global or targeted, depending on software settings. Many tonkurvor tools operate on color channels separately (red, green, blue), enabling color grading or balancing effects in addition to luminance changes.

Usage and considerations: tonkurvor are central to non-destructive workflow in many editors and are used for film-like tonality, dynamic range compression, or creative look development. They interact with histograms and can introduce clipping or banding if pushed too far. When used thoughtfully, tone curves offer precise, flexible control over image tonality and color relationships beyond simple exposure adjustments.