Color Adjustments

OpenGPEX provides professional-grade color correction and adjustment tools — all non-destructive and applied in real-time.

Accessing Adjustments

Open the Adjustments drawer from the right sidebar. All adjustment tools are organized in a unified panel with five tabs:

1. Basic — Quick sliders for common adjustments
2. Curves — Precise tonal control via curve editor
3. Levels — Histogram-based input/output adjustment
4. Channel Mixer — Advanced per-channel color control
5. Color Balance — Shadow/midtone/highlight color shifts

Basic Adjustments

Shortcut: Ctrl/Cmd + U

Five essential sliders for quick color correction:

Tips

• Adjustments are applied per-layer — select the layer you want to adjust
• Changes are non-destructive: the original image data is never modified
• Real-time preview at 60fps as you drag sliders

Curves Editor

Shortcut: Ctrl/Cmd + M

The Curves tool gives you precise control over tonal values using a graphical curve.

Channels

• RGB (Master): Adjust overall brightness/contrast
• Red: Adjust red channel independently
• Green: Adjust green channel independently
• Blue: Adjust blue channel independently

How to Use

1. Select the channel you want to adjust (RGB, R, G, or B)
2. Click on the curve line to add a control point
3. Drag control points up to brighten, down to darken
4. The curve uses cubic spline interpolation for smooth transitions

Common Curve Adjustments

• S-Curve: Drag highlights up and shadows down for increased contrast
• Brightening: Pull the midpoint of the curve upward
• Color Tint: Adjust individual R/G/B channels to shift color balance

Levels Editor

Shortcut: Ctrl/Cmd + L

The Levels tool adjusts image tonality using a histogram-based interface.

Components

• Histogram: Visual display of tonal distribution in your image
• Input Levels: Three triangular sliders (Shadows / Gamma / Highlights)
• Output Levels: Constrain the tonal range of the output

How to Use

1. The histogram shows the distribution of tones in your image
2. Drag the left triangle (shadows) inward to deepen blacks
3. Drag the right triangle (highlights) inward to brighten whites
4. Drag the middle triangle (gamma) to adjust midtone brightness
5. Use Auto button for automatic levels correction

Channel Mixer

Shortcut: Ctrl/Cmd + Shift + X

The Channel Mixer provides advanced control over how color channels contribute to the output.

Features

• 3×3 Matrix: Control how each input channel (R, G, B) contributes to each output channel
• 7 Built-in Presets: None (identity), B&W Red Filter, B&W Green Filter, B&W Blue Filter, Sepia, Cross Process, Photo Negative
• Monochrome Mode: Convert to grayscale with custom channel weights

Common Uses

• Create custom black & white conversions (B&W presets)
• Cross-process color effects (70s film look)
• Correct color casts
• Simulate film looks (Sepia, Photo Negative)

Color Balance

Shortcut: Ctrl/Cmd + B

Adjust colors independently in shadows, midtones, and highlights — ideal for creative color grading and correcting color casts.

Three Tonal Ranges

• Shadows: Affects the darkest areas of the image
• Midtones: Affects the middle brightness range
• Highlights: Affects the brightest areas

Three Color Axes (per range)

• Cyan ↔ Red
• Magenta ↔ Green
• Yellow ↔ Blue

Each slider ranges from -100 to +100 (default: 0 = no shift).

Preserve Luminosity

Enable this option to prevent color shifts from changing the perceived brightness of the image. The algorithm compensates using Rec.709 luminance weights.

Real-Time Preview

All adjustments benefit from OpenGPEX's dual-track rendering:

• Fast Track: Instant 60fps preview as you adjust sliders (uses optimized LUT lookup)
• Full Quality Track: Worker-based full-resolution rendering in the background

This means you never have to wait — adjustments feel instantaneous regardless of image size.

Next Steps

• Layer Management — Blend modes and layer compositing
• AI Tools — AI-powered enhancements
• Export & File Formats — Output with adjustments baked in

Last updated: 2026-07-30