User Guide - Color Refraction Wheels

Refraction: Color wheels for filmic color mapping

The Color Refraction wheels in the app allow you to make advanced color adjustments to your images by controlling the hue and density of colors in the shadow and highlight regions. Refraction uses an algorithmic transform model that offers much higher color mapping and density stability than conic color models like HSL or HSV while providing the same intuitive interface.

The Shadow and Highlight Refraction Wheels offer 6 color points for red, yellow, green, cyan, blue, and magenta hue vectors. You can adjust the hue of each point by moving it in an orbital motion, and desaturate or increase the color density by moving the point toward the center or outer boundary of the circle, respectively.

Keyboard Shortcuts: Hold down the Shift Key while dragging to lock a point to its current orbit for hue adjustments. Hold down the CMD (Mac) or CTRL (Win) Key to lock a point to its current angle for density adjustments. As with all other tools, double click a point to reset it back to its default position.

Separate shadow and highlight control

By default, the Shadow and Highlight Refraction Wheels are synchronized, which means that any mappings are applied to the entire luminance range of the color space. However, you can detach the wheels and make separate refraction adjustments for shadows and highlights by clicking on the link icon between the wheels.

The split point between shadows and highlights can be adjusted with the number input below the link icon, and a mask preview of the split point can be toggled by clicking the mask button below the number input. Whatever part of the mask image is black will be affected by the shadow refraction settings, while everything that is white will be affected by the highlight refraction settings.

Built-in Film Emulation and Smoothness

The Color Refraction tool in provides advanced and film-like color compression and expansion capabilities, with built-in film density and the option to make separate adjustments in the shadow and highlight regions for fine grained color control over the final image.

By moving color points closer to each other, you can perform a hue-compression of colors, while spreading them out increases color contrast. Color compression is an important aspect of film response modelling, just like allowing slightly less color density in the highlights than the shadows.

Insider Knowledge: The Refraction Tool was partially inspired by Steve Yedlin's Tetra, a custom script for Nuke that uses tetrahedral interpolation to shift colors in RGB space instead of using conic color models like HSL which aren't well suited for color grading or film emulation tasks. The Refraction tool builds upon and enhances Tetra in several ways: It uses non-linear gamut compression, hue stabilization with built-in, parametric film density emulation controlled by shapers derived from empirical film data. The UI control is an orthogonal projection of the RGB cube so that it feels almost like working with a familiar and intuitive HSL control but with much higher internal color stability.

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