RH End Tones Sculptor

🎨 Shadow & Highlight Sculpting Engine

Shape the Character of Your Shadows and Highlights Without Touching the Middle. Most colour tools treat your image as one zone. RH End Tones Sculptor splits it into two working the shadows and highlights independently using their own tint, saturation, and hue controls, while the midtones stay untouched. Designed for colorists who know exactly what they want from their blacks and their whites.

Key Features

• Independent Shadow & Highlight Controls

• Live RGB Curve Overlay

• Zone Mask Diagnostics

• Hue Shift Gated by Checkbox

RH End Tones Sculptor is a precision colour sculpting tool focused on the extremes of the tonal range shadows and highlights. It provides independent, zone-isolated control over RGB balance, saturation, and hue rotation for both ends of your image, using the Petal Color Model (IQ Projection) for all chroma operations. It also features a built-in live curve visualiser for instant feedback.

This is not a global colour balance tool. It is specifically designed to shape the character of your shadows and highlights without disturbing midtones.

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📖 Table of Contents

• 1. Core Concept
• 2. Zone Configuration
• 3. Shadow Controls
• 4. Highlight Controls
• 5. Visual Aids
• 6. Under the Hood — Petal Color Model
• 7. Node Placement
• 8. Usage Tips

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1. Core Concept 💡

The tool splits the image into two independent tonal zones Shadows and Highlights using a luminance-based mask driven by standard Rec.709 luma.

• Shadow zone: pixels below the Black Level threshold.
• Highlight zone: pixels above the White Level threshold.
• Midtones: the region between the two thresholds — untouched by default.

Within each zone, three independent operations are available:

1. RGB Balance — additive tint, applied directly in RGB space.
2. Saturation — multiplicative chroma scaling in Petal (IQ polar) space.
3. Hue Rotation — angular hue shift in Petal (IQ polar) space (optional, gated by a checkbox).

All operations are masked and blended — the strength of each adjustment falls off smoothly at zone boundaries using smoothstep, so there are no hard edges.

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2. Zone Configuration 🗺️

These sliders define where the shadows end and the highlights begin.

⚫ Black Level

Sets the upper boundary of the shadow zone.

• Default: 0.33
• Range: 0.0 – 1.0
• Pixels with luma below this value are treated as shadows. The mask fades smoothly around this threshold by the amount set in Zone Softness.

⚪ White Level

Sets the lower boundary of the highlight zone.

• Default: 0.66
• Range: 0.0 – 1.0
• Pixels with luma above this value are treated as highlights. Blends smoothly at the boundary.

🌫️ Zone Softness

Controls how gradually the shadow and highlight masks fade at their edges.

• Default: 0.1
• Range: 0.0 – 0.5
• Lower values = harder mask edge (more zone isolation). Higher values = softer, more gradual transition into midtones.
• A minimum of 0.001 is enforced internally to prevent division-by-zero artifacts.

🔗 Unite Black / Unite White

Force the RGB channels to converge to neutral luma near absolute black and absolute white, respectively.

🟦 Show Shadow Mask / 🟥 Show Highlight Mask

Diagnostic checkboxes to visualize the masks before making adjustments.

• Show Shadow Mask: Outputs the shadow mask as a greyscale image. White = fully in shadow zone.
• Show Highlight Mask: Outputs the highlight mask as a greyscale image. White = fully in highlight zone.
• Enabling both simultaneously outputs a composite view: Red = highlights, Blue = shadows, allowing you to see zone overlap or gaps in the midtone region.

Use these before grading to confirm your zones are correctly placed for the image content.

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3. Shadow Controls 🌑

All shadow controls are weighted by the shadow mask they have full strength at the darkest parts of the image and fade toward zero at the Black Level threshold.

🌑 Shadow Red / Green / Blue

Additive RGB offset applied to the shadow zone.

• Default: 0.0 (no tint)
• Range: -0.2 – +0.2
• Positive values add that primary colour to shadows; negative values subtract it (pushing toward its complementary).
• Example: Shadow Blue = +0.05 gives a cool, slightly desaturated shadow.
• Example: Shadow Red = +0.1, Shadow Blue = -0.05 pushes shadows toward a warm amber-orange.

🌑 Shadow Saturation

Multiplicative saturation scale applied in Petal (IQ polar) space, within the shadow zone.

• Default: 0.0 (no change)
• Range: -1.0 – +1.0
• 0.0: unchanged.
• -1.0: full desaturation (greyscale shadows).
• +1.0: doubles the chroma amplitude (very saturated shadows).
• This operates on the IQ projection, preserving hue angle while scaling chroma distance.

🌑 Enable Shadow Hue + Shadow Hue Shift

Applies a hue rotation to the shadow zone.

• The checkbox must be enabled before the hue shift is applied — this prevents accidental ghost shifts when the slider is at 0.0.
• Shadow Hue Shift Range: -180° – +180°
• The rotation is additive in radians internally; the polar angle of the IQ projection is shifted before converting back to RGB.

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4. Highlight Controls 💡

Mirror of the Shadow Controls, but operating on the highlight zone (pixels above White Level).

☀️ High Red / Green / Blue

Additive RGB offset applied to the highlight zone.

• Default: 0.0
• Range: -0.2 – +0.2
• Example: High Red = +0.05, High Green = +0.02 adds a subtle warm straw tint to bright areas.

☀️ High Saturation

Multiplicative saturation scale in Petal space, within the highlight zone.

• Default: 0.0
• Range: -1.0 – +1.0
• Behaves identically to Shadow Saturation but affects only bright pixels.
• Reducing highlight saturation is useful for controlling over-saturated skies or specular highlights.

☀️ Enable High Hue + High Hue Shift

Hue rotation for the highlight zone.

• Range: -180° – +180°
• Checkbox must be active for the shift to apply.

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5. Visual Aids 👁️

📈 Show RGB Curves

Overlays a real-time tone curve graph on your image, displaying how the current RGB balance settings affect each channel across the full tonal range.

What you see:

Key behaviour:

• All curves converge at absolute black (0,0) and absolute white (1,1) by design — you cannot tint paper black or paper white, which matches the real-world behaviour of photochemical film.
• The deviation from the identity diagonal shows where and how much your RGB balance is active.

Bottom-right corner swatches:

• Left swatch: shows the shadow tint + shadow saturation applied to a mid-grey reference.
• Right swatch: shows the highlight tint + highlight saturation applied to a mid-grey reference.
• Use these swatches as a quick preview of the colour temperature of each zone.

Enable Show RGB Curves after dialing in your adjustments to verify no unintended clipping occurs in either channel.

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6. Under the Hood — Petal Color Model 🔬

All saturation and hue operations use the Petal IQ Projection (also called the max-normalize polar model):

1. Normalize: Each pixel's RGB is divided by its maximum channel value, placing the normalized triplet on the unit-scaled RGB cube face.
2. Project to polar: The normalized triplet is projected to a 2D chromatic plane (opponent axes).
3. Saturation the chroma radius in this space.
4. Hue the angular position.
5. The scale (M) is preserved separately, so adjustments are fully luminance-decoupled.

This model behaves differently from HSL or HSV. It is designed to scale chroma without shifting the perceived brightness of a colour, making it particularly useful for subtle saturation work inside a scene-referred pipeline.

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7. Node Placement 🗂️

Expected pipeline:

• Scene-referred input
• DaVinci Wide Gamut / Intermediate (DWG/DI)

Recommended placement:

• After your primary balance/exposure corrections.
• Before any output transform or display mapping.
• Can be stacked: one instance for shadows, another for highlights, if you need to use different zone boundaries.

This tool should operate in DWG/DI or an equivalent scene-referred log space. Do not use in display-referred (Rec.709 video) space saturation scaling and hue shifts will behave differently and may produce clipping.

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8. Usage Tips 💬

• Start with the masks: Enable Show Shadow Mask and Show Highlight Mask to confirm your zones before touching any colour controls.
• Zone Softness first: Set softness wide enough that there are no hard bands visible at the shadow/highlight boundary, then narrow it if you need more isolation.
• RGB Balance before Saturation: The additive RGB tint and the Petal saturation scale stack additively — apply the tint first, then use saturation to control overall chroma density.
• Use Show RGB Curves to check clipping: If any of the RGB curves diverge significantly, you may be pushing highlights or shadows into clip. The convergence at 0 and 1 is informational — the actual image values can exceed this range.
• Hue shift is a scalpel, not a brush: The hue shift is gated by a checkbox intentionally. Enable it only when you have a specific colour cast to correct; using it carelessly can introduce artificial-looking colour shifts in shadows.