gamma

Apply gamma correction to adjust image brightness, particularly in midtone regions. Gamma correction is a nonlinear operation that modifies the relationship between input and output pixel values, making images appear brighter or darker while preserving detail in shadows and highlights.

Usage

Terminal

$ mediaproc image gamma <input> [options]

Basic Syntax

Terminal

$ mediaproc image gamma photo.jpg

✓ Applied gamma correction (2.2)

Terminal

$ mediaproc image gamma photo.jpg -g 1.8

✓ Image brightened (gamma 1.8)

$ mediaproc image gamma photo.jpg -g 2.8

$ mediaproc image gamma photo.jpg -g 2.2 --gamma-out 1.8

Options

Option	Alias	Type	Default	Description
`--gamma`	`-g`	`number`	`2.2`	Gamma value for correction (1.0-3.0)
`--gamma-out`		`number`	-	Optional output gamma for conversion
`--output`	`-o`	`string`	`gamma-corrected-[input]`	Output file path
`--quality`	`-q`	`number`	`90`	Output quality (1-100)
`--dry-run`		`boolean`	`false`	Preview operation without saving
`--verbose`	`-v`	`boolean`	`false`	Show detailed processing information

Gamma Values Guide

Gamma	Effect	Use Case
1.0	Linear (no correction)	Raw sensor data, special effects
1.5	Significantly brighten	Very dark images, shadow recovery
1.8	Moderately brighten	Mac OS classic display standard
2.0	Slight brighten	Film emulation, creative look
2.2	Standard (sRGB)	Default, web images, Windows standard
2.4	Slight darken	HD video standard (Rec. 709)
2.6	Moderately darken	Cinema DCI-P3 standard
3.0	Significantly darken	Maximum shadow detail preservation

Examples

1. Basic Gamma Correction

# Apply standard sRGB gamma (2.2)
mediaproc image gamma photo.jpg

# Explicit gamma value
mediaproc image gamma photo.jpg -g 2.2

# With custom output
mediaproc image gamma photo.jpg -g 2.2 -o corrected.jpg

2. Brighten Dark Images

# Moderately brighten (gamma 1.8)
mediaproc image gamma dark-photo.jpg -g 1.8 -o brightened.jpg

# Significantly brighten (gamma 1.5)
mediaproc image gamma very-dark.jpg -g 1.5 -o much-brighter.jpg

# Subtle brightening (gamma 2.0)
mediaproc image gamma photo.jpg -g 2.0 -o slightly-brighter.jpg

3. Darken Bright Images

# Moderately darken (gamma 2.6)
mediaproc image gamma bright-photo.jpg -g 2.6 -o darkened.jpg

# Significantly darken (gamma 3.0)
mediaproc image gamma overexposed.jpg -g 3.0 -o much-darker.jpg

# Subtle darkening (gamma 2.4)
mediaproc image gamma photo.jpg -g 2.4 -o slightly-darker.jpg

4. Display Calibration

# Mac display calibration (gamma 1.8)
mediaproc image gamma photo.jpg -g 1.8 -o mac-display.jpg

# Windows/sRGB calibration (gamma 2.2)
mediaproc image gamma photo.jpg -g 2.2 -o windows-display.jpg

# Cinema display (gamma 2.6)
mediaproc image gamma photo.jpg -g 2.6 -o cinema-display.jpg

5. Color Space Conversion

# Convert from linear to sRGB
mediaproc image gamma linear.jpg -g 1.0 --gamma-out 2.2 -o srgb.jpg

# Convert from sRGB to linear
mediaproc image gamma srgb.jpg -g 2.2 --gamma-out 1.0 -o linear.jpg

# Convert between display standards
mediaproc image gamma mac.jpg -g 1.8 --gamma-out 2.2 -o windows.jpg

6. Shadow Detail Enhancement

# Recover shadow details (lower gamma)
mediaproc image gamma backlit.jpg -g 1.6 -o shadow-enhanced.jpg

# Preserve shadow details (higher gamma)
mediaproc image gamma high-contrast.jpg -g 2.6 -o shadow-preserved.jpg

# Balanced shadow/highlight (standard gamma)
mediaproc image gamma photo.jpg -g 2.2 -o balanced.jpg

7. Creative Effects

# Film look (gamma 2.0)
mediaproc image gamma photo.jpg -g 2.0 -o film-look.jpg

# High contrast look (gamma 2.8)
mediaproc image gamma photo.jpg -g 2.8 -o high-contrast.jpg

# Soft look (gamma 1.8)
mediaproc image gamma photo.jpg -g 1.8 -o soft-look.jpg

8. Batch Processing

# Brighten all dark photos
for img in dark-photos/*.jpg; do
  mediaproc image gamma "$img" -g 1.8 -o "brightened/$(basename "$img")"
done

# Standardize to sRGB gamma
for img in *.jpg; do
  mediaproc image gamma "$img" -g 2.2 -o "srgb/$(basename "$img")"
done

# Apply creative gamma to series
for img in series/*.jpg; do
  mediaproc image gamma "$img" -g 2.4 -o "processed/$(basename "$img")"
done

9. HDR Processing

# Tone mapping simulation (lower gamma)
mediaproc image gamma hdr.jpg -g 1.5 -o tone-mapped.jpg

# Preserve highlight detail (higher gamma)
mediaproc image gamma bright-hdr.jpg -g 2.8 -o highlight-preserved.jpg

# Balanced HDR look
mediaproc image gamma hdr.jpg -g 2.0 -o balanced-hdr.jpg

10. Print Preparation

# Compensate for print darkening (gamma 1.8)
mediaproc image gamma photo.jpg -g 1.8 -o print-ready.jpg

# Professional print standard (gamma 2.2)
mediaproc image gamma photo.jpg -g 2.2 -o pro-print.jpg

# Newsprint compensation (gamma 1.6)
mediaproc image gamma photo.jpg -g 1.6 -o newsprint.jpg

11. Video Frame Processing

# Video standard gamma (Rec. 709 = 2.4)
mediaproc image gamma frame.jpg -g 2.4 -o video-frame.jpg

# Cinema DCI-P3 (gamma 2.6)
mediaproc image gamma frame.jpg -g 2.6 -o cinema-frame.jpg

# Web video (gamma 2.2)
mediaproc image gamma frame.jpg -g 2.2 -o web-video-frame.jpg

12. Quality Control

# Maximum quality gamma correction
mediaproc image gamma photo.jpg -g 2.2 -q 100 -o high-quality.jpg

# Web-optimized gamma
mediaproc image gamma photo.jpg -g 2.2 -q 85 -o web-optimized.jpg

# Balanced quality
mediaproc image gamma photo.jpg -g 2.2 -q 90 -o balanced.jpg

13. Preview Operations

# Preview gamma correction
mediaproc image gamma photo.jpg -g 1.8 --dry-run

# Detailed preview
mediaproc image gamma photo.jpg -g 2.6 --dry-run --verbose

# Compare different gamma values
mediaproc image gamma photo.jpg -g 1.8 --dry-run
mediaproc image gamma photo.jpg -g 2.2 --dry-run
mediaproc image gamma photo.jpg -g 2.6 --dry-run

14. Scientific Imaging

# Linear gamma for analysis (gamma 1.0)
mediaproc image gamma raw-data.jpg -g 1.0 -o linear-analysis.jpg

# Calibrated display (gamma 2.2)
mediaproc image gamma microscope.jpg -g 2.2 -o calibrated-view.jpg

# Enhanced detail visibility (gamma 1.8)
mediaproc image gamma scan.jpg -g 1.8 -o enhanced-scan.jpg

15. Combining with Other Operations

# Gamma correction then contrast adjustment
mediaproc image gamma photo.jpg -g 1.8 -o temp.jpg
mediaproc image linear temp.jpg -a 1.2 -b 10 -o final.jpg
rm temp.jpg

# Resize then gamma correct
mediaproc image resize photo.jpg -w 1920 -h 1080 -o temp.jpg
mediaproc image gamma temp.jpg -g 2.2 -o final.jpg
rm temp.jpg

# Gamma correct then sharpen
mediaproc image gamma photo.jpg -g 2.0 -o temp.jpg
mediaproc image sharpen temp.jpg -o final.jpg
rm temp.jpg

Use Cases

1. Display Calibration

Monitor Matching: Adjust images for different display types
Cross-Platform: Convert between Mac (1.8) and Windows (2.2) standards
Professional Displays: Calibrate for cinema and broadcast standards
Print Preview: Compensate for print vs screen differences

2. Photography Workflow

Exposure Compensation: Recover underexposed or overexposed images
Shadow Recovery: Brighten shadows without blowing highlights
Highlight Preservation: Darken to preserve highlight detail
Creative Looks: Apply film-like or artistic gamma curves

3. Video Production

Frame Export: Apply correct gamma for video frames
Color Grading: Base gamma adjustment before color work
Standards Compliance: Match Rec. 709, DCI-P3, or other standards
Web Delivery: Optimize for web video playback

4. Print Preparation

Compensation: Adjust for paper and ink characteristics
Proofing: Create accurate print previews
Newsprint: Compensate for low-quality paper
Professional Print: Match commercial printing standards

5. Scientific and Medical Imaging

Linear Analysis: Convert to linear space for measurements
Display Standardization: Ensure consistent viewing conditions
Detail Enhancement: Improve visibility of subtle features
Quantitative Analysis: Prepare images for scientific measurement

6. Web and Digital Media

sRGB Compliance: Ensure images display correctly on web
Mobile Optimization: Adjust for mobile device displays
Cross-Browser: Consistent appearance across browsers
Social Media: Optimize for platform-specific requirements

7. Game Development

Asset Preparation: Correct gamma for game engines
Texture Processing: Ensure textures display correctly
Linear Workflow: Convert between linear and gamma spaces
Platform Targeting: Adjust for console vs PC displays

Technical Details

Gamma Correction Formula

Basic Gamma Correction:

Output = Input ^ (1 / gamma)

Where:
- Input: Original pixel value (0-1)
- Gamma: Correction value (1.0-3.0)
- Output: Corrected pixel value (0-1)

Example Calculations:

Gamma 1.8 (brighten):
  0.5 ^ (1/1.8) = 0.614 (brighter midtone)

Gamma 2.2 (standard):
  0.5 ^ (1/2.2) = 0.730 (standard midtone)

Gamma 2.6 (darken):
  0.5 ^ (1/2.6) = 0.789 (darker midtone)

Gamma Curve Visualization

Brightness Scale (0-255)

Gamma 1.5 (brighten):
255 ████████████████ (unchanged)
128 ███████████      (brightens to ~167)
64  ██████           (brightens to ~108)
0   ░                (unchanged)

Gamma 2.2 (standard):
255 ████████████████ (unchanged)
128 █████████        (stays ~128-140)
64  ████             (stays ~64-75)
0   ░                (unchanged)

Gamma 3.0 (darken):
255 ████████████████ (unchanged)
128 ███████          (darkens to ~108)
64  ██               (darkens to ~48)
0   ░                (unchanged)

Color Space Standards

Standard	Gamma	Description
sRGB	2.2 (approx)	Web standard, Windows default
Mac OS Classic	1.8	Older Mac displays
Rec. 709	2.4	HD television standard
DCI-P3	2.6	Digital cinema standard
Linear	1.0	No gamma, raw sensor data

Gamma vs Other Adjustments

Operation	Effect	Best For
Gamma	Nonlinear midtone adjustment	Natural-looking brightness
Brightness	Linear addition	Simple lightening/darkening
Contrast	Expand/compress range	Increase visual impact
Curves	Arbitrary nonlinear	Precise tonal control
Levels	Input/output mapping	Complete tonal adjustment

Performance Considerations

Fast Operation: Simple power function per pixel
Memory Efficient: In-place transformation possible
CPU Intensive: More intensive than linear adjustments
Precision: Works in floating-point for accuracy
Color Accurate: Preserves color relationships

Gamma Out Parameter

When --gamma-out is specified:

Step 1: Decode with input gamma
  Linear = Input ^ gamma

Step 2: Encode with output gamma
  Output = Linear ^ (1 / gamma-out)

Net effect:
  Output = Input ^ (gamma / gamma-out)

Example:

# Convert from Mac (1.8) to Windows (2.2)
mediaproc image gamma mac.jpg -g 1.8 --gamma-out 2.2 -o windows.jpg

# Equivalent to:
# Output = Input ^ (1.8 / 2.2) = Input ^ 0.818
# This darkens the image slightly

Common Patterns

Pattern 1: Brighten Dark Image

# Lower gamma to brighten
mediaproc image gamma dark.jpg -g 1.8 -o brightened.jpg

Pattern 2: Darken Bright Image

# Higher gamma to darken
mediaproc image gamma bright.jpg -g 2.6 -o darkened.jpg

Pattern 3: Standard sRGB Correction

# Apply standard web gamma
mediaproc image gamma photo.jpg -g 2.2 -o srgb.jpg

Pattern 4: Display Conversion

# Mac to Windows
mediaproc image gamma mac.jpg -g 1.8 --gamma-out 2.2 -o windows.jpg

Pattern 5: Linear to sRGB

# Convert linear to display-ready
mediaproc image gamma linear.jpg -g 1.0 --gamma-out 2.2 -o srgb.jpg

Troubleshooting

Issue: Image Too Bright/Dark

Problem: Gamma correction makes image unusable

Solutions:

# Try smaller gamma adjustments
# Instead of gamma 1.5, try 1.8
mediaproc image gamma photo.jpg -g 1.8 -o moderate.jpg

# Preview different values first
mediaproc image gamma photo.jpg -g 1.5 --dry-run
mediaproc image gamma photo.jpg -g 1.8 --dry-run
mediaproc image gamma photo.jpg -g 2.0 --dry-run

# Combine with other adjustments if needed
mediaproc image gamma photo.jpg -g 1.8 -o temp.jpg
mediaproc image linear temp.jpg -a 0.9 -o final.jpg

Issue: Colors Look Wrong

Problem: Colors appear washed out or oversaturated

Solutions:

# Gamma affects all channels equally
# This is correct behavior for luminance

# For selective color adjustment, use other tools:
# 1. Adjust gamma
mediaproc image gamma photo.jpg -g 2.0 -o temp.jpg

# 2. Adjust saturation separately
mediaproc image modulate temp.jpg -s 110 -o final.jpg

# Or use curves for channel-specific control

Issue: Highlights Blown Out

Problem: Bright areas become pure white

Solutions:

# Use higher gamma to preserve highlights
mediaproc image gamma photo.jpg -g 2.6 -o preserved.jpg

# Or combine with other techniques:
# 1. Reduce exposure first
mediaproc image linear photo.jpg -b -20 -o darkened.jpg

# 2. Then apply gamma
mediaproc image gamma darkened.jpg -g 2.2 -o final.jpg

Issue: Shadows Too Dark

Problem: Shadow detail lost after gamma correction

Solutions:

# Use lower gamma to brighten shadows
mediaproc image gamma photo.jpg -g 1.6 -o shadow-enhanced.jpg

# Or apply shadow-specific adjustment:
# 1. Extract shadow region
# 2. Apply gamma to shadows
# 3. Composite back

# Or use clahe for local contrast
mediaproc image clahe photo.jpg -o shadow-recovered.jpg

Issue: Inconsistent Results

Problem: Different images need different gamma values

Solutions:

# This is normal - exposure varies
# Create processing script with conditional logic:

#!/bin/bash
for img in *.jpg; do
  # Analyze brightness first
  brightness=$(mediaproc image stats "$img" | grep mean)

  # Apply appropriate gamma
  if [[ $brightness < 100 ]]; then
    # Dark image, brighten
    mediaproc image gamma "$img" -g 1.8 -o "processed/$(basename "$img")"
  else
    # Normal/bright, standard gamma
    mediaproc image gamma "$img" -g 2.2 -o "processed/$(basename "$img")"
  fi
done

Issue: Gamma vs Brightness Confusion

Problem: Not sure whether to use gamma or brightness

Solutions:

# Use GAMMA for:
# - Nonlinear brightness adjustment
# - Preserving shadow/highlight detail
# - Display calibration
# - Natural-looking corrections
mediaproc image gamma photo.jpg -g 1.8

# Use BRIGHTNESS (linear) for:
# - Simple lightening/darkening
# - Uniform adjustments
# - Quick fixes
mediaproc image linear photo.jpg -b 30

# Gamma affects midtones most
# Brightness affects all tones equally

Best Practices

Understand Gamma Values
- Lower gamma (< 2.2) = brighten
- Higher gamma (> 2.2) = darken
- 2.2 is standard for web/Windows
- Stay within 1.5-3.0 range for natural results
Preview Before Applying
- Use --dry-run to test values
- Compare multiple gamma values
- Check highlights and shadows
- Verify overall appearance
Combine with Other Adjustments
- Gamma is one tool in workflow
- May need contrast adjustment too
- Consider color correction
- Apply sharpening after gamma
Display Considerations
- Know target display gamma
- Test on actual target device
- Consider viewing environment
- Account for ambient light
Quality Management
- Use high quality for final output
- PNG for lossless corrections
- JPEG 90+ for photography
- Consider bit depth for gradients
Batch Processing
- Test on sample images first
- Group similar exposures
- Use consistent gamma per group
- Automate with scripts
Documentation
- Note gamma values used
- Record before/after examples
- Document decision rationale
- Maintain workflow consistency

Integration Examples

With Other Image Commands

# Gamma correct then sharpen
mediaproc image gamma photo.jpg -g 2.0 -o temp.jpg
mediaproc image sharpen temp.jpg -o final.jpg

# Auto-enhance then gamma
mediaproc image auto-enhance photo.jpg -o temp.jpg
mediaproc image gamma temp.jpg -g 2.2 -o final.jpg

# Gamma then adjust contrast
mediaproc image gamma photo.jpg -g 1.8 -o temp.jpg
mediaproc image linear temp.jpg -a 1.1 -o final.jpg

# Resize then gamma correct
mediaproc image resize photo.jpg -w 1920 -o temp.jpg
mediaproc image gamma temp.jpg -g 2.2 -o final.jpg

In Scripts

#!/bin/bash
# Apply gamma correction based on image brightness

for img in photos/*.jpg; do
  filename=$(basename "$img" .jpg)

  # Get mean brightness
  mean=$(mediaproc image stats "$img" | grep -oP 'mean: \K\d+')

  # Apply appropriate gamma
  if [ "$mean" -lt 90 ]; then
    # Dark image - brighten
    gamma=1.8
  elif [ "$mean" -gt 165 ]; then
    # Bright image - darken
    gamma=2.6
  else
    # Normal - standard gamma
    gamma=2.2
  fi

  echo "Processing $filename with gamma $gamma"
  mediaproc image gamma "$img" -g "$gamma" -o "corrected/${filename}.jpg"
done