# Raking Room

A movable lamp over Iana Kochu’s *Tidal Oval*. The room stays front-on. Follow the soft red stroke, the blue-white rim and the ochre seam as they catch the light from opposite sides.

[Open the study](./) · [Light experiments](../) · [Original Tidal Oval photograph](../../assets/tidal-oval.jpg)

| Still | Lamp azimuth | Elevation above the painting surface |
| --- | ---: | ---: |
| [Upper left](cover.png) | 315° | 16° |
| [Source colour](source.png) | Diffuse wall | Photo colour |
| [Lower right](lower-right.png) | 135° | 16° |

The stills show the live renderer’s gallery wall at 822 × 820 pixels. Direction is clockwise from the top. Both sliders work with the keyboard, and **Look closer** enlarges a fixed area around the red and blue brushwork by 2.18×. **Source colour** shows the same cutout with the photo’s RGB values. Moving either slider brings the lamp back.

## How the surface is made

1. The 1600 × 1067 studio photo supplies the pigment pixels. A hand-traced outline cuts away the cloth and support around the oval. Every view uses the same cutout and samples the 548 × 800 crop at the same coordinates.
2. A shallow, rounded bevel follows the outline. Soft hand-drawn strokes add relief around the red curl, blue-white rim and a few broader areas. Band-passed photo luminance adds fine variation, with less influence near strong chroma edges where a shift in hue could masquerade as a ridge.
3. Central differences of that composite relief define a normal at each pixel. The lamp direction and elevation set the normal-based diffuse response and a restrained sheen, applied to the photo’s colour in linear light. Separate plaster shading and a soft wall shadow follow the same lamp position.
4. **Source colour** bypasses the lighting calculation. The original photo link shows the whole studio photograph with its original surroundings.

The viewing idea comes from conservation imaging. In reflectance transformation imaging, a fixed camera and an object are photographed under multiple known lamp positions. The photographs record how the actual surface responds. Here, a single existing photo supplies pigment colour and small-scale image texture, and the relief is authored. The photo includes its original lighting, and the simulated ridges, bevel and sheen represent an artistic interpretation. [Smithsonian Museum Conservation Institute on RTI](https://mci.si.edu/reflectance-transformation-imaging) · [Historic England’s multi-light imaging guide](https://historicengland.org.uk/images-books/publications/multi-light-imaging-heritage-applications/heag069-multi-light-imaging/)

## Browser checks

In headless Chrome, all 304,879 opaque cutout pixels in **Source colour** matched the corresponding decoded pixels in the original photo. The two grazing presets had identical alpha at every canvas pixel. At 130,601 opaque pixels, one preset raised the summed RGB channels by more than six levels from source colour while the opposite preset lowered them by more than six. The mean absolute difference between opposing renders was 20.30 levels per RGB channel.

Checks also covered idle stability, returning to the same lamp setting, keyboard operation of both sliders and zoom, touch presets and zoom at 390 pixels wide, and the still-image fallback with JavaScript disabled.