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Adjust

The Adjust module provides GPU-accelerated color and tone adjustments for images.

All adjust operations modify the image in-place.

Brightness

Adjusts image brightness by adding a factor to all RGB channels.

Example - Brighten:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.brightness(img, 0.2)

save(img, 'output.jpg')
Brightened image

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Example - Darken:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.brightness(img, -0.3)

save(img, 'output.jpg')
Darkened image

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Parameters:

  • image (Image): Image to adjust (modified in-place)
  • factor (float): Brightness adjustment. Positive values brighten, negative values darken

Use for: Quick exposure adjustments, creating fade effects

Contrast

Adjusts image contrast relative to middle gray (0.5).

Example - Increase Contrast:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.contrast(img, 1.5)

save(img, 'output.jpg')
High contrast

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Example - Decrease Contrast:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.contrast(img, 0.5)

save(img, 'output.jpg')
Low contrast

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Parameters:

  • image (Image): Image to adjust (modified in-place)
  • factor (float): Contrast multiplier
  • factor > 1.0: Increases contrast
  • factor = 1.0: No change
  • factor < 1.0: Decreases contrast

Use for: Making images more punchy or creating washed-out effects

Saturation

Adjusts color intensity while preserving luminance.

Example - Increase Saturation:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.saturation(img, 1.8)

save(img, 'output.jpg')
High saturation

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Example - Desaturate to Grayscale:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.saturation(img, 0.0)

save(img, 'output.jpg')
Grayscale

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Parameters:

  • image (Image): Image to adjust (modified in-place)
  • factor (float): Saturation multiplier
  • factor = 0.0: Grayscale
  • factor = 1.0: Original colors
  • factor > 1.0: More vibrant colors

Use for: Making colors pop, creating black and white images, subtle color grading

Gamma

Adjusts gamma correction (non-linear brightness). Unlike brightness, gamma affects midtones more than highlights or shadows.

Example - Brighten Midtones:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.gamma(img, 1.5)

save(img, 'output.jpg')
Gamma brightened

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Example - Darken Midtones:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.gamma(img, 0.6)

save(img, 'output.jpg')
Gamma darkened

Right-click to download and compare in full size

Parameters:

  • image (Image): Image to adjust (modified in-place)
  • gamma (float): Gamma value (must be positive)
  • gamma > 1.0: Brightens midtones
  • gamma = 1.0: No change
  • gamma < 1.0: Darkens midtones

Use for: Lifting shadows without blowing out highlights, display calibration, color grading

Opacity

Adjusts image opacity by multiplying the alpha channel.

Example - Semi-Transparent:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.opacity(img, 0.5)

save(img, 'output.png')
50% opacity

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Example - Subtle Fade:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

Adjust.opacity(img, 0.8)

save(img, 'output.png')
80% opacity

Right-click to download and compare in full size

Parameters:

  • image (Image): Image to adjust (modified in-place)
  • factor (float): Opacity multiplier
  • factor = 0.0: Fully transparent
  • factor = 1.0: No change (original opacity)
  • factor > 1.0: Increases opacity (can exceed 1.0 for pixels with alpha < 1.0)

Use for: Creating fade effects, watermarks, layering with transparency, ghost/overlay effects

Note: This operation multiplies the existing alpha channel. If the image has no alpha channel or alpha is already 1.0, values > 1.0 will have no visible effect.

Combining Adjustments

All adjustments can be chained since they modify in-place:

Example:

from pyimagecuda import load, Adjust, save

img = load("photo.jpg")

# Apply multiple adjustments
Adjust.brightness(img, 0.1)
Adjust.contrast(img, 1.2)
Adjust.saturation(img, 1.3)

save(img, 'output.jpg')

Brightness vs Gamma

Brightness adds a constant value: - Affects all pixels equally - Can wash out highlights - Good for simple exposure fixes

Gamma applies a curve: - Affects midtones more than extremes - Preserves highlight and shadow detail - Better for lifting underexposed images

Example comparison:

from pyimagecuda import load, Adjust, save

# Brightness approach
img1 = load("dark_photo.jpg")
Adjust.brightness(img1, 0.3)
save(img1, 'brightened.jpg')

# Gamma approach (usually better)
img2 = load("dark_photo.jpg")
Adjust.gamma(img2, 1.5)
save(img2, 'gamma_corrected.jpg')