Gamma controls the mathematical relationship between encoded pixel values and displayed brightness, particularly in the midtones. While contrast affects the spread between shadows and highlights, gamma specifically redistributes middle gray tones without dramatically altering the darkest shadows or brightest highlights.
The Gamma Curve
A gamma value of 1.0 represents a linear relationship: if you double the pixel value, you double the brightness. But most displays use non-linear gamma curves (typically 2.2 for monitors, 2.4 for cinema). These curves allocate more tonal values to darker tones where the human eye is more sensitive to differences, and fewer to highlights where our perception is coarser.
This non-linearity matches human vision’s logarithmic response to brightness. Without gamma encoding, linear images would look washed out on standard displays, with shadows rendered too bright and midtones lacking depth.
sRGB and Display Gamma
The sRGB color space incorporates a gamma of approximately 2.2, which has become the de facto standard for web images and general photography. Professional work sometimes uses ProPhoto RGB or Adobe RGB color spaces with different gamma curves, though the practical impact on most images is subtle.
When images are properly gamma-encoded for the viewing environment, midtones appear natural and gradients remain smooth. Gamma mismatches between capture, editing, and display cause images to appear either too light and washed out, or too dark and blocked up.
Gamma vs. Curves Adjustments
While both affect tonal distribution, curves offer more precise control over specific tonal ranges. A gamma adjustment applies a consistent mathematical transformation across all midtones. A curves adjustment allows you to target specific regions—lifting shadow detail without affecting highlights, for instance.
Think of gamma as a broad, consistent adjustment to overall midtone weight, while curves provide surgical precision. Many photographers never adjust gamma directly, preferring the granular control of curves for creative post-processing.
Linear Workflow and RAW Processing
When processing RAW files, you’re initially working with linear scene-referred data before gamma encoding. Modern RAW processors handle this transformation automatically, but understanding gamma helps when making advanced tonal adjustments or preparing images for specific output media.
Some advanced workflows deliberately work in linear gamma spaces to avoid compounding the non-linear transformations that occur with multiple adjustments. This approach requires careful handling but can maintain superior tonal integrity through complex edits.
Gamma for Different Media
Print output uses different gamma than screen display because reflected light behaves differently than emitted light. Professional printing workflows account for these differences through soft proofing and output-specific profiles. An image optimized for a 2.2 gamma display may need different midtone rendering for optimal print results.
Related Concepts
- Histogram – Shows how gamma affects tonal distribution
- Bit Depth – Determines how finely gamma curves can represent tones
- Color Space – Includes gamma specifications
- Dynamic Range – The range gamma operates across
- Clipping – Occurs when gamma adjustments push tones beyond bounds