Lumarian
Lumarian processing a natural scene with subtle edge enhancement and shadow recovery via gamma correction.
Overview
Every video image is made of three things: how bright each pixel is (luminance), what color it is (chrominance), and where the edges between regions fall. Lumarian gives you direct, real-time control over all three.
The program chains six processing stages together — contrast, brightness, saturation, gamma correction, edge enhancement, and luminance keying — and runs them simultaneously on every pixel of every frame. The name comes from luminance, the measurable brightness of light, which is the central quantity this program manipulates.
At one end of the spectrum, Lumarian can do straightforward image correction: fix a washed-out camera feed, sharpen soft footage, or pull a clean key from high-contrast material. At the other end, pushing the edge enhancer and gamma controls past their "correct" ranges produces entirely new graphic textures. The same signal chain does both — the difference is just how far you turn the knobs.
Quick Start
- Order matters: The signal flows through Contrast/Brightness → Gamma → Edge → Invert → Key. Each stage transforms the signal before the next one sees it.
- Gamma before edges: Because Gamma reshapes the luminance curve before the edge filter runs, you can use it to emphasize different parts of the image selectively. Counter-clockwise (logarithmic) lifts shadows into the filter's sensitive range, emphasizing shadow-region edges. Clockwise (exponential) does the opposite, emphasizing highlight edges.
- Eight edge modes from three switches: The three edge toggles (Switches 9, 10, 11) form a binary selector with 2³ = 8 combinations. Rather than memorizing which combination does what, sweep through all eight with Edge Gain at ~300% and a clear input — each combination produces a visibly distinct contour shape.
Background
What Is a Processing Amplifier?
Before a television signal left a broadcast station, it passed through a piece of equipment called a processing amplifier (or "proc amp"). The proc amp's job was to standardize the signal — adjusting contrast, brightness, and color saturation so that every camera, tape deck, and satellite feed looked consistent on air. Lumarian's Contrast, Brightness, and Saturation controls do exactly what a proc amp did, except digitally, operating in the YUV color space at 10-bit precision with no signal degradation.
Testing cathode ray tubes at Research Enterprises Limited, Toronto, 1942. Workers evaluated CRT lifetime for use in radar and navigation displays — the same tube technology that would later define television's nonlinear brightness response and give rise to gamma correction. Photo: Nicholas Morant / National Film Board of Canada. Public domain.
What Is Gamma Correction?
The Gamma control reshapes the transfer curve that maps input brightness values to output brightness values. Think of it this way: if you graphed "input brightness" on the x-axis and "output brightness" on the y-axis, a straight diagonal line would mean no change. Gamma bends that line into a curve — exponential (which crushes shadows and stretches highlights) or logarithmic (which lifts shadows and compresses highlights). This technique originates from the physics of CRT displays, which had a naturally nonlinear response to voltage. Lumarian lets you crossfade between both curve shapes in real time.
Left: Coating cathode ray tubes with phosphor paint at Research Enterprises Limited, Toronto, 1942. The nonlinear relationship between voltage and phosphor brightness in these tubes is the historical origin of gamma correction. Photo: Nicholas Morant / National Film Board of Canada. Public domain. Right: Gamma transfer curves — counter-clockwise (logarithmic) lifts shadow values; clockwise (exponential) crushes them.
What Is Edge Enhancement?
Lumarian's edge enhancement chain descends from a broadcast technique called aperture correction. Here is how it works: a high-pass filter extracts the spatial detail (the edges) from the luminance channel, a gain stage amplifies that detail, and the result is mixed back into the original signal. At modest settings, this simply sharpens the picture — exactly what broadcast engineers used it for. But at higher gains, the edge signal starts to overpower the source, and edges become bold graphic elements rather than subtle corrections. A rectifier with eight selectable modes (controlled by three toggle switches) determines the shape of the edge signal, turning a corrective tool into a creative one.
What Is a Luminance Key?
The Luma Blank fader implements one of the oldest techniques in video: the luminance key. It sets a brightness threshold — every pixel darker than the threshold is replaced with pure black, and every pixel brighter than the threshold passes through untouched. Television engineers used luminance keys to isolate bright objects (white text on a dark background, for example) and composite them over other sources.
Signal Flow
Y Channel → U Channel → V Channel → Sync Signals
Input Video (YUV 4:4:4)
│
├── Y Channel ──────────────────────────────────────────────────
│ │
│ ├─ 1. Contrast / Brightness (proc amp)
│ ├─ 2. Gamma Correction (exponential ↔ logarithmic curve)
│ ├─ 3. Edge Enhancement (high-pass filter → rectifier → gain mix)
│ ├─ 4. Luma Invert (bitwise complement)
│ └─ 5. Luma Blank (threshold key → black below cutoff)
│
├── U Channel ──────────────────────────────────────────────────
│ ├─ 1. Chroma Invert (bitwise complement)
│ ├─ 2. Saturation (proc amp around midpoint)
│ └─ 3. Delay Alignment (compensates for Y processing latency)
│
├── V Channel ──────────────────────────────────────────────────
│ ├─ 1. Chroma Invert (bitwise complement)
│ ├─ 2. Saturation (proc amp around midpoint)
│ └─ 3. Delay Alignment (compensates for Y processing latency)
│
└── Sync Signals ───────────────────────────────────────────────
└─ Delay Alignment (matched to total pipeline depth)
Notice that the Y channel has more processing stages than U and V. If all three channels arrived at the output at different times, the color would be misaligned with the brightness — you would see color fringes on every edge. To prevent this, the chroma and sync signals pass through delay lines that add exactly enough latency to match the Y channel. This alignment happens automatically inside the FPGA.
Parameter Reference
Videomancer's front panel with Lumarian 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 — Contrast
| Property | Value |
|---|---|
| Range | 0.0% – 200.0% |
| Default | 100.1% |
| Suffix | % |
Contrast is a gain control — it multiplies the luminance value of every pixel. At 100% (center), the multiplication factor is 1.0, so the signal passes unchanged. Turn clockwise and the factor increases: highlights get brighter while blacks stay anchored at zero. Turn counter-clockwise and the factor decreases: the entire image compresses toward black. At 0%, every pixel is black regardless of input. At 200%, every luminance value is doubled (and values that exceed the maximum are clipped).
Knob 2 — Brightness
| Property | Value |
|---|---|
| Range | -1.000 – 1.000 |
| Default | 0.001 |
Brightness is a DC offset — it adds or subtracts a constant value from every pixel's luminance. Where Contrast scales the range (multiplication), Brightness shifts it (addition). Positive values lift the whole image uniformly; negative values push it darker. This is the control to reach for when your black level is wrong — turn counter-clockwise to restore solid blacks, or clockwise if shadow detail has been lost.
Knob 3 — Saturation
| Property | Value |
|---|---|
| Range | 0.0% – 200.0% |
| Default | 100.1% |
| Suffix | % |
Saturation scales the U and V chrominance channels around their neutral midpoint. Because the scaling is centered on the midpoint (not zero), reducing saturation moves colors toward gray rather than toward a tinted value. At 0%, the output is purely monochrome — only the Y channel contributes. At 100%, color passes unchanged. At 200%, every color's distance from neutral is doubled, producing vivid, exaggerated hues.
Knob 4 — Gamma
| Property | Value |
|---|---|
| Range | -2.000 – 2.000 |
| Default | 0.002 |
Gamma reshapes the transfer curve that converts input luminance to output luminance. At center (0.000), the curve is a straight line — output equals input. Turning clockwise bends the curve downward (exponential), which darkens shadows and midtones while leaving the brightest highlights relatively unchanged. Turning counter-clockwise bends it upward (logarithmic), which lifts shadows and compresses highlights. Here is why this matters for the rest of the chain: edge enhancement runs after gamma. So if you darken midtones with gamma, edges in the shadow region become less prominent, while edges near highlights become more pronounced. This interaction gives you selective control over which parts of the image produce the strongest edge signals.
Knob 5 — Edge Gain
| Property | Value |
|---|---|
| Range | 0.0% – 400.0% |
| Default | 0.0% |
| Suffix | % |
This control sets how much of the extracted edge signal gets mixed back into the Y channel. At 0%, no edge enhancement is applied at all — the edge processing chain is effectively off. As you increase the value, transitions in the image appear sharper and more defined. Past about 100%, the edge signal starts to become as strong as the original image content. Past 200%, edges dominate the output and the original tonal information recedes into the background. At 400%, you are looking almost entirely at the edge signal itself. For reference: broadcast aperture correction typically used the equivalent of 10–30%. Anything above 100% is firmly in creative territory.
Knob 6 — Edge Cutoff
| Property | Value |
|---|---|
| Range | 0.0% – 100.0% |
| Default | 0.0% |
| Suffix | % |
Edge Cutoff sets the bandwidth of the high-pass filter that extracts edges from the Y channel. At 0%, the filter passes nothing — no edge signal is produced regardless of the Edge Gain setting. As you turn clockwise, the filter begins passing spatial frequencies, starting with the finest detail. Higher values widen the passband to include broader transitions and larger-scale contours. Edge Cutoff and Edge Gain work as a pair: Cutoff selects which edges are extracted, and Gain controls how strongly they appear.
Toggle Switches (Switches 7–11)
| Switch | Off | On |
|---|---|---|
| 7 — Luma Invert | Off | On |
| 8 — Chroma Invert | Off | On |
| 9 — Edge Invert | Off | On |
| 10 — Edge Rectify | Off | On |
| 11 — Edge Select | Single | Both |
Switches 9, 10, and 11 form a three-bit selector that chooses one of eight edge processing modes. The raw edge signal is bipolar — a bright-to-dark transition produces a positive pulse on one side and a negative pulse on the other. Edge Invert (bit 0) adds half-wave rectification, clipping the negative polarity to zero so only positive edges pass. Edge Rectify (bit 1) inverts (negates) the signal, flipping positive and negative polarities. Edge Select (bit 2) applies full-wave rectification (absolute value), folding both polarities to the same sign, which produces symmetrical contour outlines. Together, these three switches give you 2³ = 8 distinct edge shapes from the same filter output.
All eight edge mode waveforms. Each subplot shows the output shape of a single brightness transition processed through a different combination of the three edge switches.
Linear Potentiometer (Fader 12)
Fader 12 — Luma Blank
| Property | Value |
|---|---|
| Range | 0.0% – 100.0% |
| Default | 0.0% |
| Suffix | % |
Sets a luminance threshold. Any pixel whose Y value falls below the threshold is replaced with pure black (Y = 0) and neutral chroma (U = V = midpoint). Pixels above the threshold pass through unmodified. At 0%, everything passes. As you raise the fader, progressively darker portions of the image snap to black. At 100%, only the very brightest pixels survive. Because Luma Blank sits at the end of the Y processing chain, everything upstream affects what it "sees."
Guided Exercises
These exercises progress from corrective to creative, gradually exploring more of Lumarian's processing chain. Start with a clean input and build up.
Exercise 1: Correcting Camera Footage
Correcting Camera Footage — simulated result across source images. Source: A live camera feed or recorded footage with natural scenes.
What You'll Create: Learn what each of the four tonal controls does to a video signal and how they interact.
- Initialize: Load Lumarian with all defaults — Contrast, Brightness, Saturation, and Gamma at center, Edge Gain and Cutoff at zero, all toggles off, Luma Blank at zero.
- Black level: Look at the darkest parts of the image. If areas that should be black appear gray, they have a brightness offset. Turn Brightness counter-clockwise until blacks are solid. If too much shadow detail disappears, ease it back slightly.
- Contrast: Turn Contrast clockwise past center. Notice how the gap between the lightest and darkest parts of the image widens — highlights get brighter while blacks stay anchored near zero. Aim for somewhere around 110–140% for a natural-looking correction.
- Gamma: Slowly turn Gamma counter-clockwise. Shadow detail opens up because the logarithmic curve lifts dark values. Now try clockwise — midtones darken, giving the image a more dramatic character. Notice that Gamma changes the distribution of tones without changing the endpoints (black stays black, white stays white).
- Color: Turn Saturation all the way counter-clockwise to see the image in monochrome. Now bring it back past center. Notice that at 100% the color looks natural; above 100% colors become increasingly vivid and eventually start to clip.
- Sharpening: Set Edge Cutoff to about 20%, then slowly bring Edge Gain up to 30–50%. Transitions in the image become crisper — this is the digital equivalent of broadcast aperture correction.
Key concepts: Contrast is gain (multiplication), Brightness is offset (addition), Gamma is a nonlinear curve (redistribution), Saturation is chroma gain (multiplication around midpoint)
Exercise 2: Graphic Textures from Edges
Graphic Textures from Edges — simulated result across source images. Source: Footage with strong visual structure — architecture, typography, plants, fabric, or synthesized patterns.
What You'll Create: Explore what happens when the edge enhancer is pushed beyond its "correct" operating range.
- Prepare: Set Contrast to about 130% and Saturation to 0% (monochrome). This gives the edge filter a strong signal to work with.
- First edges: Set Edge Cutoff to about 40%, then slowly increase Edge Gain. Below 100%, you will see sharpening; above 100%, edges start to compete with the source material.
- Maximum edge: Push Edge Gain to 300–400%. Edges now replace most of the tonal content — the image is almost entirely made of its own contours.
- Symmetrical outlines: Enable Edge Select (Switch 11). The output changes from single-sided edges to symmetrical contour outlines.
- Mode exploration: Cycle through all eight combinations of Switches 9, 10, and 11. Each combination produces a different visual shape.
- Cutoff sweep: With Edge Gain high, sweep Edge Cutoff from minimum to maximum. At low cutoff, only the finest detail edges appear. At high cutoff, broader transitions join in.
- Gamma interaction: With edge enhancement active, turn Gamma clockwise to about 1.0. Midtones darken, and the edge filter responds differently to the redistributed tonal values.
- Color reintroduction: Bring Saturation back up. Enable Chroma Invert (Switch 8) for a complementary color effect over the edge texture.
Key concepts: Edge Cutoff selects the filter bandwidth (which edges), Edge Gain controls mix intensity (how much edge), the three edge toggles form a 3-bit mode selector (2³ = 8 modes), Gamma before edge extraction gives frequency-selective emphasis on outlines
Exercise 3: Sculpting a Luminance Key
Sculpting a Luminance Key — simulated result across source images. Source: High-contrast footage — candle flames, theatrical lighting, silhouettes, or text on a plain background.
What You'll Create: Use the full processing chain (tonal shaping → edge enhancement → inversion → threshold keying) together.
- Monochrome: Start with Saturation at 0%. Working in monochrome makes it easier to see what the luminance key is doing.
- Separate subject and background: Use Contrast and Brightness to push your subject's brightness away from the background. Increase Contrast to widen the gap; shift Brightness to move the boundary.
- Gamma shape: Turn Gamma counter-clockwise to darken midtones, making the boundary between "subject" and "background" sharper.
- Threshold: Raise the Luma Blank fader. As the threshold rises, darker parts of the image snap to black. Adjust until the background disappears and only the subject remains.
- Refine: Go back to Contrast and Brightness to clean up the key edge. Small adjustments here can eliminate fringing.
- Invert: Enable Luma Invert (Switch 7). The key flips — what was visible becomes black, and what was black becomes visible.
- Add edge outlines: With the key active, set Edge Gain to about 200% and Edge Cutoff to 30%. Edges appear within the keyed subject, adding contour detail to the silhouette.
- Colorize: Bring Saturation back up and enable Chroma Invert (Switch 8). The keyed subject now has complementary colors overlaid with edge outlines.
Key concepts: Luma Blank is a threshold comparator at the end of the chain, every upstream control changes what the threshold "sees", shaping the signal before keying is the fundamental technique for building clean controllable keys
Tips
- Feedback loops: If Videomancer's output is routed back to its input, Lumarian becomes a feedback processor. Edge enhancement and gamma correction in a feedback loop tend to produce self-reinforcing, evolving textures.
- Work in monochrome first: When building a complex effect, start with Saturation at 0%. Remove the color variable until your tonal chain is set, then reintroduce it.
- Stacking programs: Lumarian works well as either the first or last program in a multi-program chain. As the first program, it shapes the signal for downstream effects. As the last, it corrects or stylizes the final output.
Glossary
| Term | Definition |
|---|---|
| Aperture correction | A broadcast sharpening technique that extracts high-frequency detail from the luminance channel and mixes it back in at adjustable gain; the ancestor of Lumarian's edge enhancer. |
| Bipolar signal | A signal that swings both positive and negative around a zero reference; the raw edge filter output is bipolar, with opposite polarities on each side of a brightness transition. |
| Chrominance | The color information in a video signal, encoded as U and V components that represent blue-difference and red-difference offsets from neutral gray. |
| CRT (Cathode Ray Tube) | A vacuum tube display technology whose nonlinear voltage-to-brightness response is the historical origin of gamma correction. |
| DC offset | A constant value added to a signal, shifting it uniformly brighter or darker without changing contrast; the Brightness control applies a DC offset to the Y channel. |
| Full-wave rectification | Converting a bipolar signal to a unipolar one by taking the absolute value, folding negative excursions to positive; produces symmetrical contour outlines from the edge filter. |
| Gamma correction | A nonlinear transfer curve that remaps input brightness to output brightness using an exponential or logarithmic function, redistributing tonal values without changing the endpoints. |
| Half-wave rectification | Clipping one polarity of a bipolar signal to zero while passing the other, producing single-sided edge outlines. |
| High-pass filter | A filter that attenuates low-frequency content and passes high-frequency detail; extracts spatial edges from the luminance channel. |
| Luminance | The brightness component of a video signal, represented by the Y channel in YUV encoding. |
| Luminance key | A compositing technique that uses a brightness threshold to separate foreground from background; pixels below the threshold are replaced with black. |
| Proc amp (Processing Amplifier) | Broadcast equipment that standardizes video signals by adjusting contrast (gain) and brightness (offset); Lumarian's tonal controls implement a digital proc amp. |
| Transfer curve | A graph mapping input values to output values; gamma correction bends the linear transfer curve into an exponential or logarithmic shape. |