Pinwheel
Pinwheel mapping brightness gradients into a full rainbow spectrum using luminance-to-hue modulation.
Overview
Color in digital video is encoded as numbers. In YUV color space, brightness (Y) travels separately from color (U and V). Most video processors treat these channels as independent — adjust brightness here, adjust color there. Pinwheel deliberately crosses the boundary. It uses the luminance channel to drive hue rotation, mapping brightness gradients into sweeping rainbow spectra.
The program chains five processing concepts together — hue rotation via sine/cosine lookup tables, luminance-to-hue modulation, brightness and gain adjustment, chroma colorization, and bitwise crushing. The name evokes a spinning color wheel: as you sweep the Hue control, colors rotate through the full spectrum. When the Luma to Hue control is engaged, the rotation becomes adaptive — different brightness levels map to different hue angles, and a simple grayscale gradient becomes a rainbow.
At moderate settings, Pinwheel acts as a precise hue rotator and color corrector. At extreme settings with bit-crushing engaged, it produces psychedelic glitch textures where color and brightness are shattered into hard-edged digital fragments.
Quick Start
- Colorize is the key to rainbow mapping: Without Colorize, Pinwheel rotates existing colors and the output depends on the source chrominance. With Colorize, it maps brightness to color from scratch — the output is entirely determined by the luminance structure and the Hue/Luma to Hue controls.
- Brightness and Gain control output Y only: Brightness and Luma Gain adjust the output luminance level and contrast independently of the hue rotation mapping. The hue rotation angle is driven by a separate proc amp (Luma to Hue and Hue knobs).
- AND vs. XOR is the biggest toggle: fundamentally changes the character of all bit-crushing. AND is structured. XOR is chaotic. It's the difference between posterization and glitch art.
Background
What Is Hue Rotation?
In video color space, hue is the angle of the color vector in the UV plane. Red, yellow, green, cyan, blue, and magenta are arranged around a circle at 0°, 60°, 120°, 180°, 240°, and 300° respectively. Hue rotation spins all colors around this circle by a fixed angle — at 180°, every color maps to its complement. Pinwheel implements hue rotation using a full 10-bit sine/cosine lookup table, applying the standard 2D rotation matrix to the U and V components:
What Is Luminance-to-Hue Modulation?
The Luma to Hue control makes the rotation angle dependent on brightness. Instead of rotating all pixels by the same angle, each pixel gets a rotation proportional to its Y value: , where is the modulation depth and is the base Hue setting. The result: brightness gradients become color gradients. A smooth grayscale ramp becomes a smooth rainbow. Edges between bright and dark areas become edges between different hues. This is Pinwheel's signature effect — turning tonal structure into chromatic structure.
What Is Colorization?
The Colorize toggle replaces the input's chrominance with neutral (U = V = midpoint), effectively converting the input to grayscale before hue rotation. This means the output color comes entirely from the Hue and Luma to Hue controls rather than from the original source color. Without Colorize, the original colors are rotated; with Colorize, they are replaced.
What Is Bit-Crushing?
Bit-crushing applies a binary mask to the output values using AND or XOR operations. The Posterize control (Knob 5) masks the Y channel, and the Chroma Crush fader (Fader 12) masks the U and V channels. Crush Mode (Switch 10): AND cleanly zeros bits (smooth staircase quantization), XOR flips bits (chaotic, glitch-like value scrambling). AND crushing is predictable; XOR crushing is deterministic but visually wild.
Signal Flow
Y Channel → U/V Channels → Sync Signals → Bypass
Input Video (YUV 4:4:4)
│
├── Y Channel ──────────────────────────── ──────────────────────
│ ├─ 1. Proc Amp (Luma Gain × Y + Brightness offset)
│ └─ 2. Output Logic Y AND/XOR Posterize mask, optional invert
│
├── U/V Channels ───────────────────────────────────────────────
│ ├─ 1. Colorize (optional: replace UV with midpoint)
│ ├─ 2. Hue Rotation (sin/cos LUT, angle = Y × LumaToHue + Hue)
│ ├─ 3. Saturation Scaling (proc amp: UV around midpoint)
│ └─ 4. Output Logic UV AND/XOR ChromaCrush mask, optional invert
│
├── Sync Signals ───────────────────────────────────────────────
│ └─ Pass-through
│
└── Bypass ─────────────────────────────────────────────────────
└─ Select original or processed signal
Two key interactions: (1) Luminance drives chrominance: The hue rotation angle is computed from the raw Y input via a dedicated proc amp (Luma to Hue as contrast, Hue as brightness offset). This is independent of the Y-channel output proc amp (Luma Gain and Brightness). Changing Brightness or Luma Gain affects the Y output but does not change the hue rotation mapping. (2) AND vs. XOR crushing: AND is structured and predictable — it produces smooth staircase quantization. XOR is glitchy and surprising — it flips bits in a deterministic but visually chaotic pattern.
Parameter Reference
Videomancer's front panel with Pinwheel active. Knobs 1–6 (top two rows of left cluster), Toggle switches 7–11 (bottom row of left cluster), Fader 12 (right side).
Rotary Potentiometers (Knobs 1–6)
Knob 1 — Hue
| Property | Value |
|---|---|
| Range | 0.0% – 200.0% |
| Default | 100.1% |
| Suffix | % |
Base hue rotation angle. Sweeping this control rotates all colors through the spectrum — a full turn takes every color through red, yellow, green, cyan, blue, magenta, and back to red. This sets in the rotation equation. When Luma to Hue is at zero, all pixels rotate by the same angle. When Luma to Hue is active, this control shifts the starting point of the brightness-to-color mapping.
Knob 2 — Saturation
| Property | Value |
|---|---|
| Range | 0.0% – 100.0% |
| Default | 50.0% |
| Suffix | % |
Color saturation after hue rotation. This scales the rotated U and V values around the neutral midpoint. Important: Saturation operates on the post-rotation chrominance, not the original colors. At 0%, the output is monochrome regardless of hue rotation or Luma to Hue settings. At higher values, the rotated colors become increasingly vivid.
Knob 3 — Brightness
| Property | Value |
|---|---|
| Range | 0.0% – 100.0% |
| Default | 50.0% |
| Suffix | % |
Brightness offset via the Y-channel proc amp. Adjusts the DC level of the output luminance. At center, no offset. Clockwise lifts the entire image uniformly brighter; counter-clockwise pushes it darker. Note that Brightness only affects the Y output — it does not influence hue rotation (which is driven by a separate proc amp with its own controls).
Knob 4 — Luma to Hue
| Property | Value |
|---|---|
| Range | 0.0% – 100.0% |
| Default | 50.0% |
| Suffix | % |
Pinwheel's signature parameter. Controls how strongly input luminance modulates the hue rotation angle. At 0%, all pixels rotate by the same angle (set by Hue). As you increase this control, different brightness levels get different rotation angles, and a grayscale gradient becomes a full rainbow spectrum. With Colorize enabled, this control determines the entire chromatic output — the color palette is built entirely from brightness structure.
Knob 5 — Posterize
| Property | Value |
|---|---|
| Range | 0.0% – 100.0% |
| Default | 100.0% |
| Suffix | % |
Y channel bit-crushing depth. The crushing mode (AND or XOR) is set by Switch 10. In Clean (AND) mode: lower values progressively zero the least significant bits, creating a smooth staircase quantization (at maximum the full value passes unchanged). In Glitch (XOR) mode: lower values flip bits, producing chaotic, nonlinear value scrambling. The effect on the Y channel is visible as brightness quantization or brightness scrambling.
Knob 6 — Luma Gain
| Property | Value |
|---|---|
| Range | 0.0% – 100.0% |
| Default | 50.0% |
| Suffix | % |
Luminance gain via the Y-channel proc amp. Increasing Luma Gain stretches the brightness range of the output Y channel, producing higher contrast. Reducing gain compresses the output Y range. Note that Luma Gain only affects the Y output — it does not influence hue rotation (which uses a separate proc amp controlled by Luma to Hue and Hue).
Toggle Switches (Switches 7–11)
| Switch | Off | On |
|---|---|---|
| 7 — Colorize | Off | On |
| 8 — Luma Invert | Off | On |
| 9 — Chroma Invert | Off | On |
| 10 — Crush Mode | Clean | Glitch |
| 11 — Bypass | Off | On |
The five toggle switches control independent binary processing options. Colorize (Switch 7) dramatically changes the program's character by removing original chrominance. Luma Invert (Switch 8) and Chroma Invert (Switch 9) are independent inversions that interact with the hue rotation pipeline. Crush Mode (Switch 10) fundamentally changes the character of bit-crushing. Bypass (Switch 11) provides instant A/B comparison.
Linear Potentiometer (Fader 12)
Fader 12 — Chroma Crush
| Property | Value |
|---|---|
| Range | 0.0% – 100.0% |
| Default | 100.0% |
| Suffix | % |
UV channel bit-crushing depth. Independent of Posterize (Knob 5), which crushes the Y channel. The crushing mode (AND or XOR) follows Switch 10. At 100%, no crushing — full color resolution. As you lower the fader, color values are progressively masked. In AND mode, this produces smooth color quantization. In XOR mode, this produces psychedelic color scrambling. You can crush color while leaving brightness intact (high Posterize, low Chroma Crush) or vice versa.
Guided Exercises
These exercises progress from subtle color correction to extreme psychedelic processing. Pinwheel's range is enormous — the same controls produce gentle hue shifts at one end and total chromatic chaos at the other.
Exercise 1: Luminance Rainbow
Luminance Rainbow — simulated result across source images. Source: Footage with a wide range of brightness — landscapes, portraits, or gradient test patterns.
What You'll Create: Learn luminance-to-color mapping and understand how brightness becomes color.
- Colorize: Enable the Colorize toggle (Switch 7). The input chrominance is replaced with neutral — the image is now effectively grayscale.
- Activate modulation: Slowly increase Luma to Hue (Knob 4) from center toward maximum. Watch the monochrome image develop into a rainbow as different brightness levels map to different hue angles.
- Rotate the palette: Sweep the Hue knob (Knob 1). The entire rainbow palette rotates — the same brightness gradient maps to a different set of colors.
- Saturation: Adjust Saturation (Knob 2) to control color intensity. At 0%, the image returns to monochrome regardless of hue rotation.
- Brightness and gain: Change Brightness (Knob 3) and Luma Gain (Knob 6). These adjust the output luminance level and contrast but do not alter the hue rotation mapping — the rainbow remains the same, only the brightness of the result changes.
Key concepts: Colorize removes original color allowing pure luminance-to-hue mapping, Luma to Hue controls modulation depth, Hue rotates the palette, Brightness and Luma Gain control output Y independently
Exercise 2: Color Corrector to Glitch Machine
Color Corrector to Glitch Machine — simulated result across source images. Source: Colorful footage — flowers, fruit, painted surfaces, or video art.
What You'll Create: Experience the full range from subtle color correction to extreme glitch texture.
- Subtle correction: Start with a small hue rotation (Knob 1 near center). Observe gentle shifts in the color palette — this is Pinwheel as a color corrector.
- Add gain: Increase Luma Gain (Knob 6). The brightness range stretches, boosting output contrast.
- Clean crushing: Begin decreasing Posterize (Knob 5) in Clean mode (Switch 10 Clean/AND). Watch brightness quantize into smooth staircase levels.
- Glitch mode: Switch Crush Mode (Switch 10) to Glitch (XOR). The same Posterize setting now produces chaotic, scrambled brightness.
- Color crushing: Lower the Chroma Crush fader (Fader 12). In XOR mode, colors explode into psychedelic fragments.
- Compare: Toggle Crush Mode back and forth. AND is structured and predictable. XOR is chaotic and surprising. Same controls, fundamentally different character.
Key concepts: AND crushing is structured staircase quantization, XOR crushing is chaotic bit scrambling, Posterize crushes Y (brightness) and Chroma Crush crushes UV (color) independently
Exercise 3: Psychedelic Colorizer
Psychedelic Colorizer — simulated result across source images. Source: Any footage — the more varied, the more interesting.
What You'll Create: Combine all capabilities into a maximally expressive color processor.
- Foundation: Enable Colorize. Set Luma to Hue to ~80%, Hue to ~60%.
- Intensity: Boost Saturation to ~70–80%. Increase Luma Gain.
- Complement: Toggle Chroma Invert (Switch 9) for a complementary color palette.
- Total negative: Toggle Luma Invert (Switch 8) for reversed brightness.
- Crush both channels: Set Crush Mode to Glitch (XOR). Decrease Posterize to ~40%, lower Chroma Crush to ~50%.
- Animate: Slowly sweep the Hue knob. The entire psychedelic palette rotates through the spectrum — a hallucinatory, ever-shifting chromatic landscape.
Key concepts: Colorize + Luma to Hue creates pure brightness-to-color mapping, inversion and crushing compound the effect, sweeping Hue animates the entire palette
Tips
- Independent Y and UV crushing: Posterize crushes Y only. Chroma Crush crushes UV only. High Posterize with no Chroma Crush = quantized brightness with smooth color. No Posterize with low Chroma Crush = smooth brightness with quantized color. Both have distinct visual characters.
- Chroma Invert complements the palette: Instantly flip every color to its complement without changing luminance or modulation depth. Useful for quickly exploring palette variations.
- Feedback loops with hue rotation: Each feedback pass rotates hue further, creating cycling chromatic cascades that evolve over time.
- Bypass for A/B comparison: Switch 11 shows the unprocessed signal instantly.
Glossary
| Term | Definition |
|---|---|
| AND masking | A bitwise operation that zeros selected bits by combining pixel values with a mask of ones and zeros; produces smooth staircase quantization when used for bit-crushing. |
| Bit-crushing | Reducing the effective resolution of a digital value by masking or scrambling its least significant bits, producing quantization artifacts or glitch textures. |
| Chrominance | The color information in a video signal, encoded as U and V components representing blue-difference and red-difference offsets from neutral gray. |
| Color vector | The two-dimensional representation of a pixel's color as a point in the UV plane, whose angle encodes hue and whose magnitude encodes saturation. |
| Complement | The color diametrically opposite on the UV color wheel (180° rotation); Chroma Invert maps every color to its complement. |
| Hue rotation | Spinning the UV color vector around the origin by a fixed angle using a 2D rotation matrix, shifting all colors through the spectrum. |
| Luminance | The brightness component of a video signal, represented by the Y channel in YUV encoding. |
| LUT (Lookup Table) | A pre-computed array that maps input values to output values for fast evaluation; Pinwheel uses a 10-bit sine/cosine LUT for hue rotation. |
| Modulation | Varying one signal parameter (here, hue angle) in proportion to another signal (luminance), creating a brightness-dependent color mapping. |
| Proc amp (Processing Amplifier) | A circuit that adjusts a signal's gain and DC offset; Pinwheel has two Y-channel proc amps: one drives hue rotation (via Luma to Hue and Hue), the other adjusts the output luminance (via Luma Gain and Brightness). |
| UV plane | The two-dimensional chrominance space defined by the U and V axes, where angle represents hue and distance from center represents saturation. |
| XOR (Exclusive-OR) | A bitwise logic operation that outputs 1 when inputs differ; used in Glitch crush mode to flip bits chaotically rather than zero them. |